study on the air quality impacts of non-lto emissions from...

no. 3 Air pollution

"Study on air quality impacts of non-LTO emissions

from aviation"

Leonor Tarrasón and Jan Eiof Jonson

Norwegian Meteorological Institute

Terje K. Berntsen and Kristin Rypdal

CICERO, Centre for International Climate and Environmental Research- Oslo

Final report to the European Commission under contract B4-3040/2002/343093/MAR/C1

Postal address P.O.Box 43, Blindern NO-0313 OSLO Norway

Office Niels Henrik Abelsvei 40

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Telefax+47 22 96 30 50

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Swift code DNBANOKK

report

Title "Study on air quality impacts of non-LTO emissions from aviation"

Date 09.01.2004

Section Air Pollution Section, Norwegian Meteorological Institute (met.no) CICERO, Centre for International Climate and Environmental Research- Oslo

Report no. 3

Classification Free Restricted

ISSN 1503-8025

Author(s) Leonor Tarrasón and Jan Eiof Jonson (met.no) Terje K. Berntsen and Kristin Rypdal (CICERO)

e-ISSN Client(s) European Commission – Directorate General for Environment Directorate C – Environment and Health

Client’s reference Contract Agreement No. B4-3040/2002/343093/ MAR/C1

Abstract This report has been prepared under contract to the European Commission. It evaluates to what extent pollutants emitted by aircraft beyond the LTO-cycle (i.e. above 3000 feet or approximately 1000 meters) contribute to air quality problems in Europe and it is intended to support the European Commission on its review of the National Emission Ceilings Directive. Keywords aircraft emissions, acidification, eutrophication, ground level ozone, particulate matter

Disiplinary signature

Responsible signature

Postal address P.O.Box 43, Blindern NO-0313 OSLO Norway

Office Niels Henrik Abelsvei 40

Telephone +47 22 96 30 00

Telefax+47 22 96 30 50

e-mail: [email protected]: met.no

Bank account 7694 05 00628

Swift code DNBANOKK

ACKNOWLEDGEMENTS

This report has benefited from the constructive comments of the reviewers: Paul Brok, Dick Derwent, Volker Grewe, Tony Houseman and colleagues at AECMA, Arthur Lieuwen, David Lee, Michael Memmesheimer, Jana Moldanova, Nicolas Moussiopoulos, Hans Pulles, Peter van Velthoven and Peter Winkler. Special thanks are also due to Niels Ladefoged and colleagues at the European Commission for interesting discussions and comments.

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TABLE OF CONTENTS

EXECUTIVE SUMMARY .....................................................................................................................5

1. INTRODUCTION ...............................................................................................................................7

2. AVAILABLE EMISSION INVENTORIES AND AIRCRAFT EMISSION FORECASTS..............9 2.1 AIRCRAFT EMISSIONS ESTIMATED BY COMPOUND......................................................12

2.1.1. NOx ......................................................................................................................................12 2.1.2. CO and HC...........................................................................................................................14 2.1.3. SO2.......................................................................................................................................15 2.1.4. Particulate matter .................................................................................................................16 2.1.5. NH3 ......................................................................................................................................16

2.2. THE SHARE OF EUROPEAN AIRCRAFT EMISSIONS .......................................................17 2.3 OVERVIEW OF AIRCRAFT PRESENT EMISSIONS............................................................19 2.4. MAIN UNCERTAINTIES .........................................................................................................20 2.5. CONCLUSIONS ........................................................................................................................20

3. ESTIMATES OF THE ENVIRONMENTAL IMPACTS OF AIRCRAFT EMISSIONS................23 3.1. REVIEW OF EXISTING ESTIMATES OF THE ENVIRONMENTAL IMPACTS OF ATMOSPHERIC AIRCRAFT EMISSIONS ....................................................................................23

3.1.1. Climate change and UV.......................................................................................................23 3.1.2. Air quality and deposition....................................................................................................25 3.1.3. Conclusions..........................................................................................................................28

3.2. A DEDICATED MODELLING STUDY OF THE AIR QUALITY IMPACT OF NON-LTO EMISSIONS OF NOx FROM AVIATION .......................................................................................29

3.2.1. Model descriptions...............................................................................................................29 3.2.2 Experimental setup ..............................................................................................................30 3.2.3. Results on the global impact of 2000 and 2050 emissions from aviation............................32 3.2.4. Results on the regional impact in Europe of 2000 non-LTO emissions from aviation........33 3.2.5. Future impacts: results for 2015, 2020 and 2050 on the regional impact of non-LTO emissions from aviation.................................................................................................................44

3.3. CONCLUSIONS ........................................................................................................................49

4. SUMMARY AND CONCLUSIONS ................................................................................................51

5. REFERENCES ..................................................................................................................................55

6. APPENDIX: ACRONYMS AND ABBREVIAT IONS ....................................................................59

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EXECUTIVE SUMMARY The international standards regulating emissions from aircraft engines concerning their air quality impact have traditionally been addressed to emissions occurring during the landing and take-off phases (LTO) of aircraft operations. In particular, the National Emission Ceilings directive (Directive 2001/81/EC) requires Member States to limit their annual emissions of certain eutrophying pollutants and ozone precursors. The scope of the National Emission Ceilings (NEC) directive includes aircraft LTO emissions but it does not cover aircraft emissions beyond the landing and take-off cycle (non-LTO emissions). However, the directive contains a provision requiring the European Commission by the end of 2004 to “…report to the European Parliament and the Council on the extent to which emissions from aircraft beyond the landing and take-off cycle contribute to acidification, eutrophication and the formation of ground-level ozone within the Community” and to “…specify a programme of actions which could be taken at international and Community level as appropriate to reduce emissions from the sector”. The present study has been prepared under contract to the European Commission and it is intended to evaluate to what extent pollutants emitted by aircraft beyond the LTO-cycle (i.e. above 3000 feet or approximately 1000 meters) contribute to air quality problems in Europe at regional scale. Impacts of NOx emissions from aviation The study concludes that aircraft nitrogen oxide emissions above 1000 m and at cruise level (non-LTO emissions) have a small but significant impact on regional air quality levels in Europe. Nitrogen oxide (NOx) emissions from aviation affect ozone formation at ground level, increase the deposition of oxidised nitrogen, thus increasing ecosystem exposure to acidification and eutrophication. It also leads to increased regional ground level concentrations of nitrogen dioxide and particulate nitrate. The study shows that the effect on regional air quality of non-LTO emissions of NOx is generally considerably larger than that of NOx emissions in the take-off and landing phases of aviation (LTO emissions). For nitrogen dioxide, however, the effect of NOx LTO emissions on ambient air concentrations of NO2 in the vicinity of airports is not negligible and a higher impact can be expected from dedicated studies using a higher spatial resolution than the one used in the present study. For the other regional air quality indicators analysed, the non-LTO NOx emissions from aviation affect surface air quality significantly more than LTO emission. This is a consequence of the predominance of non-LTO NOx emissions (95%) over LTO NOx emissions, the atmospheric vertical exchange between the surface and the free troposphere and of the high efficiency of NOx ozone production at free tropospheric levels. It is shown that non-LTO NOx emissions contribute by year 2000 with about 2-3% to the deposition of oxidised nitrogen, and with about 1% to the air concentrations of secondary inorganic aerosols (SIA), nitrogen dioxide and mean ozone. The effect of the non-LTO NOx emissions becomes more significant with increasing ozone levels, so that it contributes with about a 5-10% increase to AOT40 and up to 30% to AOT60. In addition to the overall effects, the study also quantifies the isolated impacts of emissions occurring above the European regional domain, representing about 15% -20% of the global aircraft emissions. Despite the relatively low share with respect to global emissions, the estimated impact of this “European” share represents about half of the total impacts from non-LTO emissions of NOx, for all components except for NO2, where the contribution of aviation sources above the European domain dominate.

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The results presented here imply that any measures addressed to reduce NOx emissions from aviation should consider more in detail their influence on the non-LTO emissions. Impacts of other emissions The study has focused on NOx because available information on aircraft emissions indicates that the contribution of aviation to global emissions is larger for nitrogen oxides than for any other compounds affecting air quality. Available projections for 2015, 2050 also indicate that the expected increase in nitrogen oxide emissions from aviation is larger than for the other compounds. For other aircraft emission compounds, in particular for carbon monoxide (CO) and non methane volatile organic compounds (NMVOC), the impact on surface air quality may be larger for the LTO emission cycle than for the non-LTO phases. This is because CO and NMVOC predominantly are formed at the low power settings or idle phases that occur mainly during the LTO cycle, so that emissions at LTO cycle are about 60% of the total emissions. In areas with low NOx concentration levels, where ozone formation is VOC controlled, the effect of emissions CO and NMVOC from LTO may be more important than the effect of non-LTO emissions for the ozone surface levels. However, these aircraft emissions are considered to be small, their relative share to global emissions are an order of magnitude smaller than for NOx emissions and vary between 0.1% and 0.2%. Their effect in air quality is therefore expected to be also small. The same is the case for the emissions of sulphur dioxide (SO2). For particulate matter (PM), the available information indicates a very small contribution of primary emissions from aviation, representing less that 0.001% of the global emissions. Emissions of ammonia from aviation have not been described in the literature, and it is very unlikely that these are significant enough to cause air quality problems. Recommendations for further work This study was completed before relevant new information on emission projections from aviation was available for evaluation. The projection estimates for 2010, 2020 and 2050 presented in this study are all conservative estimates that show the lowest expected impact from aircraft emissions on surface air quality. In all given projections, the impact from aircraft emission NOx emissions is small but significant. Therefore, it is recommended to conduct further an evaluation of the impact of aircraft emissions on air quality when emission projection and cost data from CAEP/6, EUROCONTROL and EU-projects AERO2K and CONSAVE 2050 become available in 2004. The recommendation is to study further the effect of control options to reduce NOx emissions from the global aviation, in particular concerning the non-LTO cycle and include also the effect of CO and NMVOC emission reductions at LTO phases in the evaluation. Such studies should also consider the impact of meteorological variability in the overall conclusions. As more complete data on the European share of emission from aviation becomes available, it will be useful to evaluate to what extent European measures can be proved effective to improve surface air quality and deposition levels in Europe. IMPORTANT NOTICE This study is strictly confined to consider the regional air quality impacts of aviation. Other environmental problems are beyond its scope. This study does not address the considerable climate change effect induced by aviation nor the contribution of aircraft to noise pollution.

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1. INTRODUCTION Traditionally, the environmental impact of atmospheric emissions from aircraft has been addressed in two separate ways. On the one hand, air quality impacts from aviation have been considered by regulators, airports and aircraft manufacturers, focusing mainly on the emissions from aircraft occurring during the landing and take-off phases of aircraft operations (“LTO emissions”). On the other hand, studies on the environmental impact of aircraft emissions occurring in other flight phases such as climb and cruise (“non-LTO emissions”) have focused mainly on their influence on climate change, stratospheric ozone and UV-radiation. There have been a series of studies analysing the impacts of aircraft emissions on surface air quality. However, to our knowledge, the difference between the effects of LTO and non-LTO aircraft emissions on surface air quality have not been estimated before in dedicated modelling simulations. The purpose of this study is to address to what extent pollutants emitted by aircraft beyond the LTO-cycle (i.e. above 3000 feet or approximately 1000 meters) contribute to regional air quality problems in Europe. Although considerable, the contribution of aviation to other environmental problems such as climate change and noise problems is beyond the scope of the present study. The environmental problems analysed here are:

• Acidification • Eutrophication • Ground level ozone and nitrogen dioxide • Surface Particulate Matter concentrations

This study is intended to assist the Commission to fulfil its reporting requirements under the National Emission Ceilings (NEC) Directive (2001/81/EC). In 2004, the Commission shall report on the implementation of the NEC directive, and this report shall include a review of the current limitations of the scope of the directive. One of these limitations is that the Directive does not cover “emissions from aircraft beyond the landing and take-off cycle”. There is a provision in the National Emission Ceilings (NEC) directive that requires the European Commission to “…report to the European Parliament and the Council on the extent to which emissions from aircraft beyond the landing and take-off cycle contribute to acidification, eutrophication and the formation of ground-level ozone within the Community”. The Commission report shall also “…specify a programme of actions which could be taken at international and Community level as appropriate to reduce emissions from the sector … as basis for further consideration by the European parliament and the Council”. To assist the Commission in the preparation of these reports, the present study contains: • A review of existing scientific evidence and evaluations of the present and future air quality

impacts of non-LTO emissions from aviation. • Recommendations on the need for further research and studies. A review of existing estimates of the costs, benefits and reduction potentials of aircraft emissions is reported in a separate note. This report presents first a literature review of available estimates and forecasts for aircraft emissions (Chapter 2). The data has been analysed to distinguish the relative contribution of emissions occurring during landing and take-off (LTO) as compared to emissions above 1000 m and at cruise level (non-LTO). Initial indications of the contribution of European aircraft emissions – here understood as

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emissions occurring over the European territory - to the global aircraft emissions are also derived from the literature review. The contribution of non–LTO emissions to acidification, eutrophication and the formation of ground-level ozone, nitrogen dioxide and secondary aerosols in Europe is estimated in Chapter 3. Results are presented for both a literature review and a dedicated modelling approach that couples global and regional scale calculations. Local scale impacts of aircraft emissions are not explicitly considered in this study. The impact of non-LTO emissions on different regional air quality indicators is studied for the present situation (year 2000) and for projections of the situation in 2015, 2020 and 2050, derived or extrapolated from existing emission scenarios. The last chapter, Chapter 4, summarises the main findings and provides recommendations on further research activities to support the Commission under its review and possible revision of the National Emission Ceilings (NEC) Directive.

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2. AVAILABLE EMISSION INVENTORIES AND AIRCRAFT EMISSION FORECASTS

The methodology used to derive global inventories can give different results due to the use of different emission factors, traffic data, modelling assumptions and simplifications with respect to flight profiles and with respect to differences in technologies. The projections will differ due to differences in the basis for the assessment, assumptions on future growth in air transport traffic performance, technology development and phase-in of new technologies. A summary of the main aircraft emission inventories and projections is given in IPCC (1999). For the purpose of assessing the impact on non-LTO emissions on air quality, inventories with a high spatial resolution grid of emissions by latitude, longitude and altitude are needed. The main recent inventories meeting this requirement are:

• NASA (Bauchum et al. 1996a,b) • DLR (Schmitt and Brunner 1997) • ANCAT/EC2 (Gardner et al. 1997) • AERO2K/TRADEOFF (Lee, pers.comm. 2003) • AERO (AERO 2002) • EDGAR (Olivier and Berdowski 2001)

All these inventories are high quality global inventories that have different strengths and weaknesses. A summary of the differences between methods used in these global emission inventories is given in Table 1. The EDGAR data differs from the other inventories in that it is based on a top down approach using total aviation fuel supplied (statistics from the International Energy Agency). The top down approach gives higher estimates for total emissions. This is partly because bottom up inventories are likely to loose some activities and partly because most bottom-up inventories listed here are based on great circle distances between airports, and not real flight routes. On the other hand top-down inventories may have problems to distinguish between fuel used for aviation and for example stationary combustion and may consequently double-count emissions. AERO2K is an on-going 5th Framework Research Project that will provide a revised inventory of CO2, NOx, HC, CO and soot particles for a base year of 2000. The methodology accounts for real routings using Eurocontrol/FAA data supplemented with OAG scheduled data assigned to routes. It will also provide a forecast for 2025. The project is scheduled to finish in 2004, so that data are not yet available. The 5th Framework Research Project ‘TRADEOFF’ also required aviation emissions data for 2000. This was calculated in a simplified way using the ‘FAST’ inventory and scenario model. FAST utilizes the ANCAT/EC2 methodology implemented in a more flexible software system. A year 2000 estimate of NOx, CO2 and km travelled was made for the TRADEOFF project by projecting the 1992 ANCAT/EC2 movements database, according to the regional flow data used in the FESG/IPCC scenarios. Historical improvements in fuel efficiency were assumed, whilst an independent study showed that NOx had increased by only a small amount, so that this was held constant with the ANCAT/EC2 estimation1. 1 Traffic growth in the nineties was found to be according to the IPCC high growth scenario, while the ratio of NOx emissions and fuel use had increased slightly, and was kept constant.

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The TRADEOFF inventory has the most recent base year for the analysis, provides projections to 2050, has the finest altitude resolution and has the most sophisticated modelling of the non-LTO emissions. Consequently, the TRADEOFF data are used in the analysis of the effect of non-LTO emissions on air quality (Chapter 3). It will be shown in Section 2.1 that the differences between the results of the different inventories are not very large. Consequently, the conclusions from the model study in Chapter 3 are not expected to be very sensitive to the choice of inventory data.

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Table 1. Summary of different methods to estimate past and present emissions from aviation Inventory Most

recent historical year

Method Resolution Traffic movements

Estimates of fuel use and emissions

Forecast years

Key forecast assumptions

ANCAT/EC2 1992 Bottom up from aircraft movements

1*1°*1km Air traffic control data combined with scheduled movements. Jets only. Assuming great circle aircraft movements.

Modelling using 20 representative aircraft types, taking into account the entire flight cycle (including steps in cruise for each aircraft type).

2015 and 2050.

Same methodology as historical emissions, traffic and fleet forecast model, including economic assessments. Assuming an annual fuel efficiency of 1.3 % from 2000 to 2010, decreasing to 1 % from 2010 to 2015.

AERO2K

2000

Bottom up from aircraft movements

Variable Air traffic control data, taking into account real flight distances (e.g. due to congestion)

As ANCAT/EC2, with a reconsideration of representative types

2025 See NASA projection

TRADEOFF 2000 (partly based on projections)

Bottom up from aircraft movements

Infinitely variable, 1*1°*610 m utilized

Air traffic control data, and scheduled data, analysis of vertical distribution of traffic

As ANCAT/EC2 but remodelled by aircraft type with analysed average cruise altitude by mission distance NOx calculated from DLR fuel flow methodology

2050 See NASA projection

NASA 1992 Bottom up from aircraft movements

1*1°*1km Scheduled jet and turboprop. Estimates for charter, military and general aviation. Assuming great circle aircraft movements.

Manufacturers’ performance information for each aircraft-engine type, data from ICAO 1995 and a standard flight profile.

2015 and 2050.

Growth in traffic: average 5 % per year. Same method as for historical emissions, taking into account changes in technology (assuming a continuation of the historical trend + assuming that present state-of-the art technologies are phased in 2015).

DLR 1992 Bottom up from aircraft movements

2.8*2.8°*1km

As ANCAT /EC2. Scheduled air traffic only. Assuming great circle aircraft movements.

Using a flight and fuel profile model. Different aircraft-engine combinations from ANCAT. No-step cruise modelling.

2015 As ANCAT (but using a different base year).

AERO 1992+1997 Bottom up from aircraft movements

Optional; Standard: 5*5°*1km; Earlier output: 1*1°*0.5km

Unified traffic database consisting of ICAO, US DoT, ABC/OAG and ANCAT data.

Modelling using representative aircraft types; using a flight and fuel and emissions profile model; including step cruise modelling;

2010 + 2020

Optional; user-preferred selection of parameter values

EDGAR 1990+1995 Top down from fuel use. Gridded data based on aircraft movements, scaled to total fuel use.

1*1° grid cell for LTO. Gridded data for non-LTO will be available at a later stage.

- Fuel use multiplied by emission factor, which is allocated to a grid cell.

- -

Source: based on IPCC (1999) and recent information from AERO2K, TRADEOFF, AERO and EDGAR

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2.1 AIRCRAFT EMISSIONS ESTIMATED BY COMPOUND

In this chapter the available evidence of the emissions of pollutants with potential regional impact on air quality (NOx, CO, HC (VOC)2, SO2, particulate matter and ammonia) will be discussed. Most aircraft emission inventories focus on emissions of carbon dioxide (CO2) and nitrogen oxides (NOx). This is due to concerns about global effects of NOx in the stratosphere, but NOx is also most important for tropospheric ozone formation and consequently for both the regional and global effects of emissions from aviation. Thus, the focus of the review of emissions from aviation presented in this chapter will be on NOx. 2.1.1. NOx

NOx from aircraft engines mainly originates from nitrogen in the air since aviation fuel contains only trace amounts of nitrogen (IPCC 1999). NOx emission inventories are based on individual aircraft or groups of similar aircraft and modelling of emissions according to how the engine is used in different phases of the flight. Basic LTO emission factors are based on certification data (ICAO data bank)3, while non-LTO emissions are modelled based on i.a. fuel burn and NOx indices data derived from the certification data. This modelling requires data on flying distances, flying height and engine use. Often it is assumed that the flying distances are the shortest possible following a “great circle”. However, this is not always the case since many flights are restricted to follow assigned flight corridors, leading to longer flight distances than those following a great circle. A summary of the results of the various inventories is given below in Table 2. According to Schumann and Ström (2001) fuel use and emissions may be about 15% higher than estimates in bottom-up inventories as given in Table 2. The difference may be even larger for NOx, where they have estimated emissions to be as high as 2.9 Tg in 2000.

2 While NMVOCs (non-methane volatile organic compound) or VOCs usually are used in regulations of national and regional emissions (for example under the EU emission ceiling directive) and CLRTAP (the Convention on Long Range Transport of Air Pollution in Europe)), HC is regulated for aviation emissions from the LTO cycle (Landing Take off cycle). It is however normally assumed that NMVOCs are equal to HC subtracted methane. 3 The international standards regulating emissions from aircraft engines are based on performance under standardised test conditions simulating a landing and take off reference cycle ( the ICAO LTO cycle). The emission values represent standardised indicators for the amounts of pollutants emitted at four typical thrust settings and timings to represent the total emissions of nitrogen oxides (NOx), smoke, unburned hydrocarbons and carbon monoxide (CO) below 3000 feet.

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Table 2. Summary of different estimates and projections of NOx (as NO2) emissions from aviation (including military aviation*). Global total (LTO and non-LTO) emissions (Tg) Inventory Fuel used

in early nineties

Fuel used in 2000

Projected fuel used in 2015

Projected fuel used in 2050

NOx emissions in early nineties

NOx emissions in 2000

Projected NOx emissions in 2015

Projected NOx emissions in 2050

ANCAT/EC2 131.3 - 287.9 633.2 1.81 - 3.53 4.5 TRADEOFF 131.0 167.7 - 471.0 1.81 2.32 - 7.2

NASA 139.4 - 308.6 471.0 1.67 - 4.12 7.2

DLR 129.3 - 285.0 1.80 - 3.57

AERO (excl. military!) 134.2 166.0 (1997) 257.8 (2010) 368.6 (2020)

- 1.69 2.16 (1997) 3.49 (2010) 5.05 (2020)

-

EDGAR 167.8** - - - 1.88 - - -

Source: based on IPCC (1999), EDGAR-database (Olivier and Berdowski 2001) and results from TRADEOFF and AERO (2002) * The EDGAR data may only to some extent include military (depending on the reporting of countries to the International Energy Agency) ** Estimated from CO2 emissions, assuming an emission factor of 3.13 kg/kg fuel. Globally NOx emissions from aviation account for about 2 % of total emissions according to the EDGAR database (Olivier and Berdowski 2001, based on a top down estimate). Most of these emissions are from the non-LTO phase of the flight. According to the ANCAT/EC2 aircraft emission inventory (Gardner et al. 1997; Schumann 1996), the average LTO fraction of NOx emissions was about 6%, which can be compared to an average LTO fraction of 5% of the fuel. The LTO-fraction will however be considerably larger for regional and short distance trips compared to the global average. For example, it will be about 14 % for a Boeing 737-400 for a 1000 nautical miles (nm)4 flying distance and 7 % for a 2000 nm distance (EEA 2002). In the TRADEOFF emission inventory used in the model simulations in Chapter3 for year 2000, 6.3 % of the global emissions occur in the two lowest flight levels (below about 1200 meters). Over Europe (hereafter defined as the region 10ºW-20ºE and 34º-62ºN) this fraction increases slightly to 7.1% due to a larger fraction of short-haul flights. Changes in emissions over time can be explained by:

i) Increased demand for air transport ii) Increase in fuel efficiency due to both engine technology development and aircraft design. iii) Changes in aircraft fleet age and size iv) Changes in engine technology affecting NOx emissions v) Changes in aircraft operations, including routings and flight altitudes, such as the recent

implementation of the Reduced Vertical Separation Minima (RVSM). The increase in fuel efficiency has been large, but does not outweigh the increase in demand for air transport. Both fuel used and NOx emissions have been increasing as a consequence of the increased demand for air transport. Increased fuel efficiency has also resulted in increased emissions of NOx per unit fuel burned (IPCC 1999). However, new combustion technologies can reduce NOx emissions as described in a separate note on abatement possibilities (Rypdal et al., 2003). In spite of improvements in engine technology, NOx emissions have grown by about 30 % from the early nineties to 2000 (TRADEOFF). The projections indicate a doubling of fuel used from early nineties to 2015. The NASA projection gives more than a doubling of corresponding NOx emissions, 4 1 nm = 1.852 km.

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while the projected emissions grow less in the ANCAT inventory. For 2015, the different projections differ by 14% due to different assumptions about the phase-in of NOx reduction technologies (IPCC 1999). However, the real uncertainty may be larger due to large uncertainties in the future demand for air travel. The ANCAT projection assumes an annual increase in passenger kilometres of 3.9% whereas the Traffic Forecasting Sub-Group of CAEP has estimated a new projection to 2020 with a 4.3 % average annual growth5 (see also separate note by Rypdal et al., 2003). A projection using updated information about possible phase-in of aircraft engines meeting stricter NOx standards is provided in RAND (2003). This projection shows that emissions in 2020 may be 17 % lower than in a reference scenario, only assuming that technologies available today are phased in. However, there will still be a growth in total emissions due to increased air transport. This projection (even the reference scenario) estimates lower emissions in 2015 than the projections in Table 2. The TRADEOFF projection indicates that NOx emissions will triple from 2000 to 2050. Long-term projections (2050) are evidently very uncertain. IPCC (1999) presents three scenarios based on the NASA/FESG projections (high, low and base case) where the results vary according to differences in assumptions about future technology and traffic volume. In the long-term projections it is taken into account that the future rate of growth in air traffic will probably be smaller than in the past. However, none of the scenarios represents possible situations where air transport is heavily regulated, e.g. that short distance flights are substituted by other transport and/or communication modes. Furthermore, NOx-projections are made for two technology scenarios, one with design features permitting moderate NOx reductions (fleet average 10-30% below CAEP6/2 limits by 2050), and another with design characteristics allowing substantial NOx reductions (50-70% below CAEP/2 limits by 2050). A projection was also made based on the ANCAT inventory. The results of this projection are in the range of different NASA scenarios, fuel use being in the upper range and NOx emissions in the lower. Long-term projections by different scenarios were also provided by Environmental Defence Fund (IPCC 2001; Vedanthan and Oppenheimer 1998). These projections of NOx are rather similar to the NASA projections. One of the present activities initiated within AERONET (a European Union thematic network) is to provide long-term scenarios of aviation and its emissions (http://www.aero-net.org). The EC project CONSAVE 2050 (Constrained Scenarios on Aviation and Emissions) will provide updated projections of emissions from aviation until 2050, using the AERO modelling system, taking into account changes in technology, air traffic management as well as socio-economic factors). The work will be finished in 2004, and thus it has not been possible to include their results in the present overview. The data used for the modelling of the scenario for 2050 in Chapter 3 were based on NASA projections as described in the TRADEOFF inventory. 2.1.2. CO and HC

Emissions of CO and HC (VOC) are formed due to incomplete combustion of fuel. These emissions are less important for the ozone formation and air quality than NOx emissions (WMO-UNEP, 1995; IPCC, 1999; Pleijel, 1998). This is because in the relative low NOx environment of the free troposphere, ozone production will generally be NOx limited (cf. IPCC (1999, page 136)) and not CO/HC limited. Thus, adding a NOx molecule from an aircraft in the free troposphere increases ozone more effectively than a CO or HC molecule.

5 Preliminary information to the CAEP steering group meeting, June 2003. 6 Committee on Aviation Environmental Protection under ICAO.

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Of the inventories discussed above, the EDGAR inventory and projection include CO emissions whereas the NASA aircraft inventory includes CO as well as HC. Emission factors for CO and HC on an equivalent format to ANCAT/EC2 were also derived as a part of the EU project COST/MEET7 (MEET 1999), but this project did not provide global total emissions. The results are compared in Table 3. Table 3. Summary of different estimates and projections of HC and CO emissions from aviation (including military aviation). Global total (LTO and non-LTO) emissions (Tg). Ratios in g/kg fuel burned. Inventory HC

emissions in early nineties

Projected HC emissions in 2015

CO emissions in early nineties

Projected CO emissions in 2015

HC/fuel ratio in early nineties*

HC/fuel ratio in 2015

CO/fuel ratio in early nineties*

CO/fuel ratio in 2015

NASA 0.32 0.33 1.57 2.27 2.3 1.1 11.3 7.4

AERO (excl. military) 0.42 0.35 (2010) 0.41 (2020)

1.01 1.25 (2010) 1.62 (2020)

3.1 1.4 (2010) 1.1 (2020)

7.5 4.8 (2010 4.4 (2020)

EDGAR - - 1.4 - - - 8.4 -

Source: based on IPCC (2002), EDGAR-database (Olivier and Berdowski, 2001) and AERO (2002), *fleet average The NASA and EDGAR data on CO emissions are in fairly good agreement, while AERO data are lower. Global emissions of CO from aviation account for only 0.1-0.2 % of total global anthropogenic emissions. 17 % of global aviation CO emissions originate from fuel sold in Europe. Emissions of HC from aviation account for about the same fraction8. The NASA and AERO data for HC are in reasonable agreement. Typically, the LTO-fractions of total aviation emissions are far larger for HC and CO than for NOx (again depending on the distance of the flight). For a Boeing 737-400 flying 1000 nm, the LTO fractions of HC and CO emissions are about 60 % (EEA 2002 based on ANCAT/EC2). The reason for this high LTO-fraction compared to NOx is that CO and HC are formed at the low power settings / “idle” phases that occur mainly during the LTO-cycle. NOx emission indices (emission per unit fuel burned) are small at “idle” phases and high during take-off, but a considerable proportion will be formed during cruise conditions because more fuel is burned during this phase of the flight (IPCC 1999). The NASA projection indicates close to a 50 % growth in CO emissions from early nineties to 2015, while HC emissions remain rather stable. The AERO projections gives the same picture. Projected emissions of HC and CO per unit fuel used are estimated to be reduced by 34 and 52 %, respectively.

2.1.3. SO2

Global sulphur dioxide (SO2) emissions from aviation are expected to be relatively small and originate from the sulphur content of fuel. According to IPCC (1999), the average sulphur content of jet kerosene ranges from 0.04 to 0.06%, and 0.05 % is a “typical” average sulphur content (MEET, 1999). We use the fuel (CO2) data from EDGAR to estimate SO2 emissions. This gives an estimate of global SO2 emissions from aviation of 0.15 Tg (using 0.05 % sulphur content), which is about 0.1 % of the global total (global SO2 emissions were 154.3 Tg in 1990 according to EDGAR). The LTO fraction will be as for fuel use (∼ 5 %).

7 Methodologies to Estimate Emissions from Aviation 8 Based on the NASA estimate of emissions from aviation and global total emissions from the EDGAR database

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2.1.4. Particulate matter

Combustion of jet kerosene is a source of particulate matter. These emissions are regulated by ICAO measured as smoke number. There is, however, not very much information about the global or European emission level nor about the emissions measured as PM10 or PM2.5. Some information is available on PM10 and PM2.5 emissions (Petzold et al. 1999; Döpelheuer and Lecht 1998). PM10 emission factors for B737 and DC10 are about 0.01 g/kg fuel, and somewhat larger for older aircraft. The main mass fraction of the particle emission is in the accumulation mode for fine particles with particle diameter less than 2.5µm (PM2.5)

9. Döpelheuer and Lecht (1998) give emissions at different stages of the flight for an A300 aircraft. Cruise emission factors are lower than at take-off /descent (0.0067 g/kg vs. 0.05/0.01). The CEIPMEP10 database only gives emission factors for LTO, which are consistent with information above for low to medium emitting aircraft. To get a rough assessment of the order of magnitude of particulate matter emissions from aviation, we multiply the NASA estimates of fuel used in early nineties with the above mentioned emission factor values. This results in a global estimate of roughly 1.39Gg. In a similarly rough estimate of European aviation PM10 emissions, we assume that 5 % of fuel used takes place during LTO and an average emission factor for the two “technologies”. Fuel use for the EU-15 countries was derived from the EDGAR dataset (allocated according to fuel sold). Applying the emission factors above gives a European emission of 0.2 Gg in the non-LTO phase, which can be compared to total PM10 emissions of 2030 Gg for EU-15 (CEPMEIP). The LTO fraction of the emissions is about 18-20 % of the total aviation emissions. This results in European aviation emissions of PM10 of 0.25Gg that correspond to about 18% of the estimated global PM10 emissions from aviation, which is consistent with the European share for other compounds. These values are highly uncertain and should only be considered as indicative of the small contribution of aircraft emissions to particulate matter. Based on these estimates, aircraft emissions of primary PM10 over Europe would represent less than 0.01% of the total primary PM10 European emissions. Consequently, the air quality impacts of primary PM10 emissions from aviation are considered to be negligible when compared to ground-level sources. It must be underlined that this does not imply that they may not play an important role for cloud formation or other mechanisms affecting the global climate. 2.1.5. NH3

There is no indication in the literature of aviation being a source of atmospheric emissions of ammonia.

9 Emission factors for older aircraft are larger and with a larger average size fraction. 10 Co-ordinated European Programme on Particulate Matter Emission Inventories. TNO, the Netherlands. http://www.air.sk/tno/cepmeip/

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2.2. THE SHARE OF EUROPEAN AIRCRAFT EMISSIONS

The emission data from the different studies mentioned above has not been directly related to the origin and departure of each flight. Therefore, it is not possible from the available data to deduce the contribution from the European Union to the estimated emissions. The estimates from the AERO2K will be based in real traffic routes, so the actual information on the origin and departure of each flight should be available to AERO2K. However, at the time of this study only aggregated gridded values of emissions were available. In this study, the share of European aircraft emissions has been considered as the share of total aircraft emissions that occur over the European area11. For NOx emissions, this represents a share of 15% which we have used in Chapter 3 in order to be consistent with the modelling estimates on the impact of aircraft emissions on air quality. This estimate is rather similar to EDGAR’s estimate that Europe’s contribution to global NOx emissions from aviation was 20 % in 199512 (Olivier and Berdowski 2001)13. More refined estimates of the share of European aircraft emissions are not possible at the moment with the available emission data. It is expected that more detailed aircraft inventory information will be available in the future. Table 4 gives an overview of European flights’ contribution to global aviation demand in 199514. The table shows that more than 1/3 of global aviation is connected to flights within Europe or to/from Europe. If we allocate 50 % of a flight between Europe and another continent to Europe, the share is approximately ¼ of global aviation. Table 5 shows the actual total passenger-kilometres flown from European airports, most (60 %) of the European flights are from the EU-15 countries. The accession countries and EEA/Switzerland contribute with only 2 and 3 %, respectively. These two tables can be used to give an indication of the importance of emissions from intra-European flights compared to flights in/out of Europe and within and between other regions. They provide, however, only an indication as due to differences in aircraft size, flying patterns, flying distances, age and type of fleet etc., emissions will not be proportional to the traffic demand. Fuel use allocated to country sharing international emissions between country of origin and departure is shown in Table 6. 20 % of global fuel use is allocated to the EU-15 countries using this method. The TRADEOFF inventory indicates that the share of LTO emissions in European NOx emissions is somewhat larger (6% global, 7% Europe). Since NOx is mainly emitted at cruise, this would mean that

11 European area defined as the region 10ºW-20ºE and 34º-62ºN 12 National and international air traffic, allocated to the region where the fuel was sold. 13 Table 5 gives a far higher figure on flights related to European activities. It is, however, important to bear in mind that it generally can be assumed that the fuel connected to flights from another region to Europe is purchased in that region, and is not allocated to Europe in the EDGAR database. 14 All Europe, covering more countries than the European Union member countries. From the CO2 data by country in the EDGAR database (Olivier et al 2001x), it can be derived that about 90 % of total fuel sold in Europe in the early nineties can be allocated to the EU-15 countries.

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shares of the LTO emissions of species mainly released during the LTO cycle, as CO and HC, would be slightly higher in Europe than the global average. Table 4. Traffic demand by region in 1995. Share of total global revenue passenger kilometres. % Intra Europe* 12.5 Europe - North America 11.0 Europe – Asia 5.3 Europe - other regions 7.7 Total European share 36,5

Source: IPCC (1999), * Not including the former Soviet Union states. Table 5a. Aircraft kilometres flown from European EU airports under instrument flight rules during 2000 (billion km)

Total (billion km) Share

Domestic 1179,4 18% Other EU 2696,9 42% Sub-total EU 3876,4 60% Overseas territories 29,6 0% Accession countries 133,1 2% EEA (inc. Switzerland) 178,0 3% Other Europe 37,8 1% Other regions 2222,8 35 % Total 6477,7 100% Source: Eurostat based on data from EUROCONTROL

Table 5b. Aircraft fuel use in 1992 where fuel use connected to international flights is shared between country of arrival and departure (D. S. Lee 2003, pers. comm.)

Country/region Allocated fuel

use (%) United states 39,2 Japan 5,6 Canada 4,7 United Kingdom 4,7 Germany 3,8 Soviet Union 3,1 France 2,8 Spain 2,2 Australia 2,1 Brazil 1,8 Italy 1,6 Remaing EU 4,9 Other european 2,9 Other 20,5

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2.3 OVERVIEW OF AIRCRAFT PRESENT EMISSIONS

Table 6 presents an overview of the emissions from aviation as derived from the literature review summarised in the sections above. The emission values given in Table 6 are valid for 1990s and present situation. It should be noted that most approaches give approximately the same results for a given year. The percentage values presented in Table 4 differ for the different columns. Percentage of aircraft emissions are with respect to global emissions. The percentage for aircraft emissions in Europe provides a value of the contribution of European emissions to global aircraft emissions. The European share for NOx emissions has been derived from AERO2K/TRADEOFF estimates. For CO, VOC/HC and SO2, the share has been derived as an average from the share of fuel used and the estimated shared for NOx emissions. For PM10, the European share was derived from the rough initial estimates derived in section 2.1.4. The contribution of non-LTO emissions is considered with respect to total emissions from aircraft. For nitrogen oxides (NOx) and sulphur dioxide (SO2), the emissions in the non-LTO phases are dominant and constitute over 90% of the total aircraft emissions. For carbon monoxide (CO) and non-methane volatile organic compounds/hydrocarbons (NMVOC/HC) the emissions during take off and landing dominate and constitute about 60% of the total emission. The ratio between the LTO and the non-LTO share has been assumed to be the same for global and European aircraft emissions, except in the case of NOx, where documentation exist that indicates that the share of LTO emissions is somewhat larger in short distance flights. The ratio between LTO and non-LTO emissions may change in the future if:

i) The average trip length changes. Longer average trips will imply a larger non-LTO fraction.

ii) Technologies affects non-LTO emission differently from LTO-emissions (ref. section 4.1.3)

Table 6. Overview of emissions from aircraft by compound for present situation (1990s- year 2000). Source: based on IPCC (1999) and recent information from AERO2K/TRADEOFF and EDGAR. . The numbers given in brackets for NOx refers to the EMEP area used in the calculations in section 3. 1. Global

emissions 2. Aircraft emissions (% of 1.)

3. Aircraft Europe (% of 2.)

4. Non-LTO emissions (% of 2.)

5. Non-LTO Europe (% of 3.)

NOx (Tg(N)/yr) 33.8 0.71 (2.1%) 0.11 (15 %) 0.64 (94%) 0.103 (93%)

CO (Tg/yr) 861 2.0 (0.2%) 0.31 (16%) 0.80 (40%) 0.12 (40%)

NMVOC (Tg/yr) 159.5 0.32 (0.2%) 0.050 (16 %) 0.13 (40%) 0.02 (40%)

SO2 (Tg /yr) 154.3 0.15 (0.1%) 0.0265 (16%) 0.14 (95%) 0.025 (95%)

PM10 (Gg/yr) 134 60015 1.39 (0.001%)15 0.25 (18 %)15 1,1 (80%)15 0.2 (80%)15

Fuel used - 207* 49 (16%) (95%) (95%)

* Fuel sold in 2000 according to IEA

15 Please note that these data on particulate matter emissions from aviation are very uncertain.

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Table 7 presents an overview of the relative contribution of aircraft emissions over European area to total anthropogenic European sources. It is shown that NOx emissions are the only emission component with significant although small contribution to European total emissions. Table 7. Comparison of total European anthropogenic emissions in with aircraft emissions over the European area. European anthropogenic emission values reported to UNECE/EMEP for year 2000.

European area

emissions

Aircraft emissions over

Europe

Contribution of aircraft emissions to

European area emissions

NOx (Gg (N)) 6,401 110 1.7 % CO (Gg) 62,252 310 0.5 % NMVOC (Gg) 14,042 50 0.35 % SO2 (Gg) 24,146 26.5 0.1 % PM10 (Gg) 5,217 0.25 0.005 % Source: based on Vestreng (2003) for European area emissions, IPCC (1999) and recent information from AERO2K/TRADEOFF and EDGAR

2.4. MAIN UNCERTAINTIES

Data on NOx emissions and in particular fuel consumption are expected to be more certain than the inventories for other pollutants. Different inventory data sets are in good agreement. It is, however, important to bear in mind that all of them partly are based on the same data (for example data from the ICAO databank), so that uncertainties may be slightly higher than the range of different results indicate. Uncertainties can be up to 40 % according to EEA (2002) but only 20 % in a recent high quality inventory (Schumann and Ström, 2001). Top down inventories based on great circle distances between airports may underestimate emissions. This problem is likely eliminated or reduced in the TRADEOFF inventory used in this project. For the HC/NMVOC inventory, the speciation (profile of different components of the gas) is very uncertain. Data on particulate matter are indicative only. For the current assessment uncertainties in historical emission data are probably smaller than the uncertainties in the abilities of the chemical transport model (CTM) to handle transport, mixing, chemical transformations and removals accurately as described in Chapter 3. Projected emissions are evidently more uncertain than historical emission data, the uncertainty is particularly high for the future growth in air transport and changes in technology in 2050.

2.5. CONCLUSIONS

From the above review of literature on emissions it is expected that non-LTO emissions of in particular NOx potentially have a non-negligible effect on local and regional air quality, e.g. through the formation of ozone. Aviation’s contribution to total NOx emissions is significant (∼ 2%) and the non-LTO fraction of these emissions is high (> 90%). The relative contribution from aviation to the total global emission of other air pollutants is about one order of magnitude smaller (∼ 0.2 % or less) and thus less significant. CO and HC emissions from aircraft constitute a small fraction of the total global emissions. In addition, the photochemical ozone production in the free troposphere is more effective for NOx than

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CO or HC. The lifetime of NOx is shorter than for CO and many hydrocarbons, which means that relative importance of direct emissions in the free troposphere is larger for NOx than for CO or HC since most of the NOx emitted from surface sources is oxidized close to the ground. Based on these considerations, CO and HC emissions from aircraft have not been included in the modelling studies reported in section 3.2. This is consistent with the approach taken by other assessment studies. Aviation is a source of primary particulate matter, but emissions are very small compared to EU-15 total PM10 emissions (less that 0.01%). Given the estimated very small relative contribution to PM10 over Europe, non-LTO emissions of primary PM are unlikely to contribute significantly to air quality related problems and we have chosen not to include these emissions explicitly in the calculations. In Chapter 3 then, the effect of aircraft emissions on PM atmospheric levels is considered only through the contribution of gaseous precursors to secondary inorganic particles. Emissions of ammonia from aviation have not been described in the literature, and it is very unlikely to be the cause of any air quality problems. Thus the modelling assessment in the next chapter has been restricted to NOx emissions from aviation and aims to distinguish between impacts from LTO and non-LTO emissions and from global and European flight emissions.

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3. ESTIMATES OF THE ENVIRONMENTAL IMPACTS OF AIRCRAFT EMISSIONS

3.1. REVIEW OF EXISTING ESTIMATES OF THE ENVIRONMENTAL IMPACTS OF ATMOSPHERIC AIRCRAFT EMISSIONS

3.1.1. Climate change and UV

Although not the focus of this study, an overview on the effects on climate and ozone from the different components of emissions from aviation is presented in Table 8 (from IPCC, 1999). In terms of climate change, aircrafts emit greenhouse gases, such as carbon dioxide (CO2) and water (H2O). In addition NOx emissions lead to ozone formation below 18-20 km. The increase of ozone, in turn, impacts on the general atmospheric chemistry, leading to a more rapid decay of methane, the later being an important greenhouse gas. The net effect of NOx from aircraft is believed to be positive (stronger warming by ozone enhancement, than cooling by methane reductions), but the magnitude remains uncertain. Aircraft emissions of water vapour may also cause warming if persistent line-shaped condensation trails (contrails) are formed. SOx emissions can modify the optical properties of the aerosols in the contrails. Soot particles from aviation emissions have a similar effect as sulphate particles since these will scatter incoming radiation hence leading to radiative cooling. However, the dominant effect of soot particles will be absorption of sunlight thus leading to a net warming effect. Recent developments and on-going research Since the IPCC (1999) report the development in our understanding of the climate impact of aircraft has mainly been on the relative importance of the impact of contrails and cirrus clouds. Recent models (Schuman and Strøm, 2001; Marquart et al., 2002) suggest that the radiative forcing (RF) of line-shaped contrails is about half compared to the estimates made by IPCC (1999). On-going studies (EU funded project TRADEOFF, final report submitted to DG research (G. Amanatidis)) of cirrus clouds based on satellite observations of trends in cirrus cloud coverage combined with data on regional trends in aircraft emissions indicate that the RF caused by increased cirrus cloud coverage in these regions might be a factor of 2-3 larger than those estimated as global averages by IPCC in 1999.

Figure 1. Estimated climate impact (in terms of radiative forcing) caused by emissions from aircraft in 1992 and 2050, from IPCC (1999). Note that recent research suggests that the role of aviation in cirrus clouds is a factor of 2-3 larger than indicated here, and that the impact of aviation in contrails is about a factor of 2 smaller than in these IPCC 1999 estimates.

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Table 8. Species contributing to climate and ozone change (From IPCC, 1999).

Emitted Species Role and Major Effect at Earth’s Surface CO2 Troposphere and Stratosphere

Direct radiative forcing warming H2O Troposphere

Direct radiative forcing warming Increased contrail formation radiative forcing warming

Stratosphere Direct radiative forcing warming Enhanced PSC formation O3 depletion enhanced UV-B Modifies O3 chemistry O3 depletion enhanced UV-B

NOx Troposphere

O3 formation in upper troposphere radiative forcing warming reduced UV-B Decrease in CH4 less radiative forcing cooling

Stratosphere O3 formation below 18–20 km reduced UV-B O3 depletion above 18–20 km enhanced UV-B Enhanced PSC formation O3 depletion enhanced UV-B

SOxO and H2SO4 Troposphere

Enhanced sulfate aerosol concentrations Direct radiative forcing cooling Contrail formation radiative forcing warming Increased cirrus cloud cover radiative forcing warming Modifies O3 chemistry

Stratosphere Modifies O3 chemistry

Soot Troposphere

Direct radiative forcing warming Contrail formation radiative forcing warming Increased cirrus cloud cover radiative forcing warming Modifies O3 chemistry

Stratosphere Modifies O3 chemistry

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3.1.2. Regional air quality and deposition

A number of modelling studies has been performed over the last years with the aim to estimate the impact of aircraft emissions on the atmospheric composition (Brasseur et al., 1996; Flatøy and Hov, 1996; Jones et al., 1996; Meijer et al., 1997; Sausen et al., 1997; Stevenson et al., 1997; Wauben et al., 1997; Dameris et al., 1998; Grewe et al., 1999, Berntsen and Isaksen, 1999; Kraabøl et al., 2000, 2003). In addition, three recent assessments (Brasseur et al., 1998; IPCC, 1999; Schumann and Strøm, 2001) have addressed these issues. None of these studies or assessments has considered the question related to the impact of non-LTO emissions on air quality in the planetary boundary layer (PBL) specifically. The reason for this is that results from the chemical tracer models (CTMs) applied in these studies have indicated that changes in surface air pollution are fairly small compared to the potential impacts on climate and UV through changes in total atmospheric ozone concentrations. Ground-level ozone and nitrogen dioxide It should be noted that even with the substantial effort by the modelling community to improve the CTMs there are still significant uncertainties and shortcomings in the ability of CTMs to simulate the detailed chemical composition of the free troposphere (Brunner et al., 2003). In particular modelling the surface ozone effects of emissions above the planetary boundary layer (PBL, surface to 200m-2km depending on location and time) is difficult due the importance of the interaction between chemistry and mixing (cf. Berntsen and Isaksen, 1999). Nevertheless, models have to be applied to quantify these effects as the impact of non-LTO (or even total aircraft emissions) can be extracted from observations. Figure 2 shows estimates of zonally and monthly averaged ozone enhancements due to NOx emissions from aircraft in 2015 (1.08 Tg(N)/yr) in three global CTMs (AEROCHEM-II, 2000). The changes in ozone are 1 pbbv or less during the northern hemisphere (NH) summer (July) when enhancement of surface ozone above 40 ppbv is a major air quality issue. These ozone changes include also LTO emissions. During episodes with enhanced surface ozone levels the contribution from aviation can be expected to be even smaller. This is due to the fact that ozone episodes occur when the local production is enhanced by clear skies and little dilution of pollutants (e.g. during stable high-pressure situations during summer). With this kind of weather and circulation patterns transport of air (and thus pollutants) from the free troposphere above the boundary layer is slow and the impact on surface concentrations is probably small. This has, however, not been investigated in detail by CTMs by calculating correlations between surface enhancements of ozone or nitrogen dioxide (due to aircraft emissions) and the background surface concentrations of ozone. This could also be analysed by generating power spectrums (see Grewe et al., 2001) of surface contributions from aircraft. Acid deposition and eutrophication In terms of deposition issues related to acidification and eutrophication, the emissions of sulphur from aviation is very small compared to the ground based sources (about 0.1 Tg(S)/yr (0.1%) for current emissions (Brasseur et al., 1998). The NOx emissions are more important being about 2% of the total global anthropogenic emissions. However, due to the longer lifetime of NOx at cruise altitude, and the more rapid transport of the emissions from aviation, it is expected that NOx from aircraft will be spread on a hemispheric scale. Thus the contribution to local or regional problems from non-LTO emissions will probably be small. A quantitative estimate of the contribution to nitrate deposition in Europe is given in section 3.2. Particulate matter Aircraft emissions of PM10 in the upper troposphere/lower stratosphere are expected to be very small (0.001% of the global PM10 emission). Soot and sulphate particles from aircraft are of sub-micron size, which are mainly removed from the free troposphere by wet deposition. While these small particles can be of significant importance for radiative forcing and upper troposphere cloud formation, the

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published estimates show that the potential impact on surface air quality is very minor. Weisenstein et al. (1997) estimated that the enhancement of soot concentrations at the surface due to aviation was between 0.05 and 0.1 ng/m3 or 5% of the concentration changes at cruise altitude. Typical concentrations of soot at the surface are 500-1000 ng/m3 (Cooke and Wilson, 1999). Based on Pitari et al. (2001) it can be estimated that the total contribution from aircraft sulphur emissions (LTO + non-LTO) to aerosol mass at ground level is 0.005-0.010 µg/m3 as a zonal mean at 40ºN. This is likely to be a upper constraint since it is based on a calculation of the removal of a fossil fuel tracer (Danilin et al., 1998) thus neglecting the more efficient wet scavenging of sulphate particles. Health effects of high level of particles are typical urban problems (much more so than ozone or acidification), with environmental standards (PM2.5 and PM10) of 20-300 µg/m3 (www.nilu.no) as diurnal average levels. These concentration changes are so small (about 0.01%) that consequently, the effect on regional air quality from LTO and non-LTO emissions can be considered to be negligible.

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Figure 2. Zonally averaged enhancement of tropospheric ozone (ppbv) due to NOx emissions from aircraft in 2015 in the LCTM (Univeristy of l’Aquila, Italy, upper panels), the OCTM, (OsloCTM2, middle panels) and the DLRGCM (lower panels) models, for January (left) and July (right). Regions where the changes are not significant are shaded (DLRGCM only) From AEROCHEM-II, 2000.

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3.1.3. Conclusions

Due to the fact that more than 90% of the emissions from aviation takes place in the free troposphere and that the low sulphur content of the fuel and the efficient combustion in aircraft engines reduce emissions of pollutants other than NOx and CO2, the focus of research on environmental impacts of non-LTO emissions from aviation have been on climate and ozone/UV issues. Results from global CTMs with relatively crude spatial resolution, have indicated that the NOx emissions can lead to surface ozone enhancements of up to 2 ppbv. In terms of other potential surface air quality impacts (acidification, eutrophication, and particulate matter) the influence of aircraft emissions, and thus even more so for non-LTO emissions, have so far been qualified by the scientific community (cf. the references cited above in particular the three assessment reports; Brasseur et al., 1998; IPCC, 1999, Schumann and Strøm, 2001) as minor and no quantitative analysis has been carried out in the reviewed literature. For nitrogen dioxide, studies have concentrated on the local impacts in the vicinity of airports due to LTO emissions and little attention has been given to the comparison of the impact from non-LTO emissions.

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3.2. A DEDICATED MODELLING STUDY OF THE AIR QUALITY IMPACT OF NON-LTO EMISSIONS OF NOX FROM AVIATION

Since the regional air quality impact of non-LTO aircraft emissions has not been considered explicitly in the reviewed literature, a dedicated study was set up here to provide a first indication on the extent these emissions from aircraft may affect air quality levels in Europe. The main focus of the analysis is on enhancement of ground-level ozone, impacts on acid deposition and eutrophication by oxidised nitrogen deposition as well as increases of aerosol surface concentrations and regional levels of nitrogen dioxide. This air quality impact study is concerned only with NOx emissions from aircraft because emissions from all other air quality components (CO, HC, SO2, NH3 and PM10) are so small compared to ground level sources that their contribution to regional scale air quality problems is considered to be of little significance. 3.2.1. Model descriptions

The global chemistry transport model OsloCTM2 has been used to calculate concentrations at the boundaries of the regional Eulerian EMEP model. The results from the global model are needed because changes of atmospheric concentrations due to emissions in the free troposphere are having affects at much greater distances than emissions close to the surface, and thus aircraft emissions outside Europe can have an effect within Europe. The use of boundary conditions from the global model secures that the regional model will also take into account the effect of aircraft emissions outside Europe in the results. The Eulerian EMEP model The EMEP model is a multi-layer atmospheric dispersion model for simulating the long-range transport of air pollution over several years. The EMEP model has 20 vertical layers up to 100 hPa (about 16 km altitude, tropopause level) and is primarily intended for use with a 50*50km2 horizontal resolution in the EMEP polar stereographic grid. The model used in the study is based on previous versions of the EMEP Eulerian photooxidant (Jonson et al., 2000, 2001) and acid deposition (Jakobsen et al., 1997) models. The present version of the EMEP model includes 72 species and ca. 140 reactions. It uses the same photochemical scheme as the Lagrangian EMEP model that has been extensively peer-reviewed (Simpson, 1995; Andersson-Sköld and Simpson, 2001), and has been extended to include secondary inorganic particles and primary particulate matter (EMEP Report 5/2001, EMEP Report 5/2002). While the numerical structure and physical description of advection/transport have been revised in the new Eulerian EMEP model, the descriptions of emissions, chemical transformation processes and wet and dry removal processes are similar to those previously developed and validated in the Lagrangian EMEP model. A detailed description of the model can be found in EMEP Report 1/2003, PART I. The model uses meteorological data from a dedicated version of the operational HIRLAM model (High Resolution Limited Area Model) maintained and verified at the Norwegian Meteorological Institute. The anthropogenic emission input data are national emissions reported per sector and grid officially reported to the Convention on Long-Range Transboundary Air Pollution through the UNECE Secretariat. The scientific team at the Norwegian meteorological institute checks the emission data for completeness and consistency and derives temporal profiles for use in the EMEP models (Vestreng, 2003). The temporal profiles of emission data are provided by the GENEMIS project under EUROTRAC-2. Emissions are emitted into different heights above the surface according to sector.

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The EMEP model has been recently developed to include a new parameterisation of dry deposition that enables the calculation of ozone fluxes to vegetation (Emberson et al., 2001). This approach allows an alternative calculation of ecosystem exposure to ozone based on actual ozone flux/deposition to vegetation. The new approach is called “ozone level II approach” and is presently under evaluation for use in the impact assessment of vegetation damage and in integrated assessment modelling. Since the ozone level II approach is still under testing, the vegetation damage calculations presented here are based on traditional concentration threshold approaches. All versions of the EMEP model use flexible boundary conditions provided either by observations or modelled results from global air pollution models. Validation of the EMEP Eulerian model against observations for different years can be found in EMEP Report 1/2003-PART II. A preliminary version of the model was validated against ozone sonde measurements in Jonson et al. (2002). A previous model version was used in the EU project POLINAT (Jonson et al., 1999). The global Oslo-CTM2 model The OSLO-CTM2 is an off-line chemical transport model that uses pre-calculated transport and physical fields to simulate the global chemical turnover and distribution in the troposphere. The maximum horizontal resolution of the model is determined by the input data provided. Currently a data set based on ECMWF forecast data with a 1.875° or ~200 km resolution is used. In the vertical the model has 40 levels from the surface up to the stratosphere at 10 hPa. The chemical scheme includes 55 chemical compounds and 120 gas phase reactions in order to describe the photochemistry of the troposphere (Berntsen and Isaksen, 1997; Berntsen and Isaksen, 1999). Photodissociation rates are calculated on-line, following the approach described in Wild et al. (2000). Emissions of nitrogen oxides from lightning are coupled on-line to the convection in the model using the parameterization proposed by Price and Rind (1993) and the procedure given by Berntsen and Isaksen (1999). The mixing in the planetary boundary layer is treated according to the Holtslag K-profile scheme (Holtslag et al., 1990). Influence of stratospheric ozone is estimated using a synthetic ozone approach (McLinden et al., 2000) where the ozone flux from the stratosphere is prescribed, but the model transport generates an ozone distribution that varies with time and space. The model has been used to study global effects on tropospheric ozone and oxidation capacity of aircraft emissions (Kraabøl et al., 2002) The simulations used for the calculations of the boundary concentrations for this study have been done with a version of the model with a coupled troposphere/stratosphere chemistry developed by Michael Gauss (Gauss and Isaksen, manuscript in prep.) during the EU project TRADEOFF. 3.2.2 Experimental setup

The study focuses on the impacts of the main primary pollutant from aviation, NOx, using the most recent emission inventory for the year 2000 prepared for the EU-funded projects AERO2K/TRADEOFF. According to this inventory the total global NOx emissions from aviation are 0.71 Tg(N)/yr (or 2.32 Tg(NO2)/yr). The global CTM has been run with and without the emissions of NOx from aviation to provide the boundary concentrations for the regional CTM (EMEP model). Three of the regions neighbouring the European/EMEP model region have no significant LTO emissions these are the mid-Atlantic, the Arctic, and the Sahara. In the fourth neighbouring region, Russia, the emissions are non-negligible but these take place on down-wind side of the European regional domain. In addition, LTO emissions take place in the atmospheric boundary layer where the lifetimes of pollutants are short. It is therefore expected that the inclusion of LTO emissions in the global CTM does not impact the boundary concentrations significantly. In other words, LTO

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emissions from Europe will affect European air quality and we do not expect the LTO emissions from other continents to have a significant impact over Europe. The regional EMEP model has been used to perform four simulations:

1. Including all aircraft emissions of NOx (LTO + non-LTO). Boundary conditions (BC) from the global simulation with aircraft.

2. Including only the non-LTO emissions from aircraft. Boundary conditions (BC) from the global simulation with aircraft.

3. Including only the non-LTO emissions from aircraft. Boundary conditions (BC) from the global simulation without aircraft.

4. No emissions from aircraft. Boundary conditions (BC) from the global simulation without aircraft.

Because of the non-linearity of atmospheric chemistry, individual contributions to air quality are derived as difference between different model run. In this experiment we analyse the contribution of the following sources:

I. Effect of European LTO emissions: The effect of the European LTO emissions is the difference between simulations 1 and 2.

II. Effect of global non-LTO emissions: The effect of non-LTO emissions over the European area can be derived from the difference between simulations 3 and 4.

III. Effect of global non-LTO emissions: The difference between simulation 2 and 4 can be interpreted as the effects of all non-LTO emissions globally, since we do not expect the LTO emissions from other continents to have a significant impact over Europe, as explained above.

In the calculations all emissions within the EMEP model domain are counted as European emissions. Thus roughly 50% of the trans-Atlantic flights are counted as European emissions. LTO and non-LTO emissions from Europe can be extracted from Table 6. In the real atmosphere some of the non-LTO emissions and the secondary pollutants formed by the emissions over Europe might move out of the region and then circle the globe, re-entering the European region (and the domain of the regional CTM) from the west. This is very difficult to model with our current model setup (requires a two-way coupling of the models), but the effects are of course smaller than what we define as the global impact (difference between simulations 2 and 4 above). This set up has been chosen to minimise the number of runs required to determine the separate contribution from European LTO and non-LTO emissions. With this set-up, the contribution of European LTO and non-LTO is made using two slightly different background concentrations. Due to the non-linearities of the ozone/NOx chemistry it could be argued that the results are biased by the choice of the calculation set up, since the 1-2 difference removes the LTO emissions from the background including all the aircraft emissions, while the difference 2-4 adds the non-LTO emission to a background without aircraft emissions. The possible non-linear effects are however extremely small since concentration changes of NOx in the boundary layer (0 to about 2 km altitude) due to the non-LTO emissions of NOx are small, less than 10 pptv (for the total aircraft emissions, e.g. Dameris et al., 1998; Wauben et al., 1997) out of a typical background of 1 ppbv or more. The non-linearity of the ozone production per NOx molecule (molecules of ozone per extra molecule of NOx as function of the NOx background) has been calculated by Lin et al. (1988). At a NOx background typical for the boundary layer over Europe of 1 ppbv of NOx the ozone production is about 20 ozone molecules per added molecule of NOx, decreasing to about 9 at a background of 10 ppbv of NOx. This means that an ‘error’ of the order of 10 pptv in the NOx background of 1 ppbv can cause an ‘error’ of 0.1% in the ozone production by using the difference between the simulations 1 and 2 for the LTO effect instead of performing a new

32

simulation similar to 3 but adding only the LTO emissions. This is clearly negligible and we do not believe that the choice of the set-up will change the results on the non-LTO contribution. Both the global and the regional model have been run with year 2000 meteorology. The meteorological conditions will differ from one year to another. A persistent high pressure system over Europe will result in higher ozone concentrations, and also affect the stability and thus the mixing of air from aloft into the boundary layer. Inter annual variation in precipitation will cause differences in the deposition patterns. For ozone, variations of aircraft impact caused by meteorological variability have been estimated to be 20% (IPCC, 1999). Calculated and measured concentrations and depositions of a number of pollutants are also compared in EMEP (2003).

3.2.3. Results on the global impact of 2000 and 2050 emissions from aviation

Figure 3 shows the monthly mean ozone concentration changes derived from the global OSLO CTM2 model for year 2000. The NOx emissions from aviation also cause changes of other nitrogen species (such as HNO3, PAN) as well as the OH radical, which induces perturbations of CO and NMVOCs. The results from the OsloCTM2 model for these species have also been used as boundary conditions for the regional CTM.

Figure 3. Monthly mean ozone perturbations (ppbv) for July caused by the 2000 global NOx emissions from aviation (LTO+non LTO).The left panel shows the zonally averaged change, while the right panel shows the change at cruise altitude (10 km).

Figure 4. As figure 3 but for 2050 NOx emissions from aviation.

33

Simulations for the 2050 case, using the NASA 2050 emission scenario for aviation (2.18 Tg(N)/yr from aircraft) and IPCC SRES A2 scenario for surface emissions (NOx: 71.1 Tg(N)/year, CO: 1428 Tg(CO)/year, VOC: 225 Tg(C)/year) have also been performed. The results for ozone are shown in Figure 4. Note that the maximum perturbation of ozone occurs at 10 km altitude over northern hemispheric mid latitudes. The magnitude of the impact at 40˚- 60˚ latitude and 10 km altitude is about 4 ppbv in 2000 emission conditions and about 8 ppbv increase in 2050. At surface level, however, the increase of mean ozone is below 1 ppbv in 2000 and below 2 ppbv in 2050. These estimates are consistent with IPCC published reports (see section 3.1.2). 3.2.4. Results on the regional impact in Europe of 2000 non-LTO emissions from aviation

Ozone The results presented here focus first on the perturbations in surface ozone during summer (April-to September), since this is the period of the year with the highest ozone concentrations over Europe. Summer is also the season with maximum vertical mixing in the atmosphere, which can cause downward transport of ozone enhancements caused by emissions above 1 km (non-LTO). The results from the regional model simulations for 2000 emission conditions are presented in the figures below. Figure 5 shows the enhancement of average daily maximum ozone concentrations during summer, while Figure 6 shows the average increase during the 10 days with the highest maximum ozone concentrations (1 hour mean) over the entire year. For the daily averaged maximum ozone the increase is less than 0.3 ppbv for the “European case” (caused only by non-LTO emission in Europe), while the global non-LTO emissions can increase the effect to 0.4-0.6 ppbv over Europe. The maximum enhancement over the Sahara is caused by subsidence of air in this region, and slower loss of ozone through surface deposition due to lack of vegetation. These values are consistent with the global model simulation, by the Oslo CTM2 model. The impact of surface ozone is often given in terms of accumulated ozone exposure (in ppbv hours) above a given threshold ozone concentration. For impact on vegetation the threshold is set to 40 ppbv ozone concentration defining the AOT40 value as:

∑=

−=n

iiOAOT

13 )40(40 for O3>40 ppbv, where n is the number of hours (i) with daylight

where the threshold is exceeded. The sum is calculated for the period between April and September in order to assess the impact on forests (AOT40f). Figure 7 shows the calculated increase in AOT40f for forests in Europe due to the inclusion of non-LTO emissions. The enhancement of the AOT40f values in the case of global reductions of non-LTO emissions (lower panel) reach 1,000-1,500 ppbv hours over Southern parts of Europe. This corresponds to an enhancement of 5-10 % over the Iberian Peninsula and the Balkans. Over Italy and Central Europe the relative changes are smaller (2-5%). The AOT60 index is defined similarly to the AOT40f index, but with a threshold of 60 ppbv ozone. As shown in Figure 8, the increase in AOT60 due to non-LTO emissions is largest over high altitude terrain (i.e. the Alps) where the background levels are closer to the threshold of 60 ppbv due to influence of free tropospheric air with higher ozone concentrations. In relative terms the impact is largest over Southwest Europe (Spain and Portugal) and Southeast Europe (Greece, Turkey, Romania and the former Yugoslavia). The increase is as much as 20-30 % although the absolute change in daily maximum ozone is only 0.4-0.6 ppbv (Figure 5), and 0.8-1.0 ppbv during ozone episodes (Figure 6). This due to the fact that surface ozone concentrations are already close to the threshold in these areas, and thus only a small absolute increase can increase the number of hours exceeding the threshold significantly.

34

In average, the increase in summer mean ozone at the surface level due to non-LTO global emissions is of the order of 1%. The effect of the non-LTO emissions becomes more significant with increasing ozone level, so that it contributes to about a 5-10% increase for AOT40f and up to 30% for AOT60. In all cases, the contribution of global non-LTO emissions (simulation 2 versus simulation 4) is dominant over the effect of non-LTO emissions over the European area (simulation 3 versus simulation 4). This is a consequence of the emission assumptions used in the model calculations, where the aircraft emissions over the European area constitute only a 15% of the global emission. However, it should be noted that European non-LTO emissions contribute about 50% (somewhat less to the mean ozone concentrations and somewhat more to AOT60) relative to the effect of global non-LTO emissions on surface ozone in Europe. The LTO emissions in Europe account for about 1% of the total global NOx emissions from aircraft. To quantify the impacts of non-LTO emissions on air quality in Europe, it is possible to exclude other emissions but NOx since the free troposphere is a NOx-limited photochemical regime with respect to ozone formation. However, the LTO emissions are usually injected into polluted air that is not NOx limited and where the hydrocarbons have significant role in ozone formation. Additionally, it is at the LTO cycle when the majority of hydrocarbons are emitted and their role is likely to be non-negligible. Nevertheless, we have restricted our simulations of the impact of the LTO emissions to the effect of NOx because the main purpose of this study is to understand the potential effect of the non-LTO emissions. Eventually this might lead to a proposal for regulations of non-LTO emissions where the focus ought to be on NONOxx. The calculated impacts of LTO emissions (lower right panels in Figures 5-11) should then be interpreted as impacts of NOx emissions in the LTO cycle, and be used as a measure for how any changes in NOx emissions in the LTO cycle due to regulations of non-LTO NOx emissions affects air quality. Based on this we conclude that the non-LTO NOx emissions are significantly more important than LTO emissions of NOx for European air quality. However, this is not to say that the total (including NMVOC) LTO emissions may not have noticeable effects on a more local scale near airports. Deposition of oxidized nitrogen NOx emitted from aviation leaves the atmosphere through wet and dry deposition of NOx but mainly as other oxidized species like nitric acid (HNO3), peroxyacetylnitrate (PAN), or particles containing nitrate ions (NO3

-). The atmospheric lifetime of oxidized nitrogen species is shorter than that of ozone, thus the non-LTO emissions from aircraft outside Europe has less effect within Europe than what is the case for ozone (cf. Figures 5-8). Figure 9a shows the increase in dry deposition of oxidized nitrogen due to non-LTO emissions from aircraft, while Figure 9b shows the increase in the wet deposition of oxidized nitrogen. The relative importance of non-LTO emissions is 2%-3% or less within Europe in all cases. Both for wet and dry deposition non-LTO emissions outside Europe (simulation 2 versus simulation 4) increase the enhancement of the deposition by about 50% compared to the Europe only results (simulation 3 versus simulation 4). The impact on wet deposition is somewhat larger than for dry deposition since the processes of in-cloud and below-cloud scavenging affects directly the pollutants in the free troposphere where the non-LTO emissions take place. The contribution of LTO emissions to the total deposition of oxidised nitrogen is about an order of magnitude smaller than for the non-LTO emissions and is mostly localised surrounding airport areas. Non-LTO emissions, however affect deposition of oxidised nitrogen more homogeneously over Europe as a consequence of the efficient horizontal mixing and the long lifetime of the pollutants emitted in the free troposphere. Deposition of oxidised nitrogen contributes to the acidification and eutrophication of ecosystems. Exceedance values are defined as the excess deposition above the critical loads for different ecosystems. The contribution of a particular pollution source to exceedances of critical load of

35

acidification or eutrophication is the same as their contribution to deposition. Thus, in areas where ecosystems are exposed to exceedances of critical loads, the contribution from non-LTO sources will be of the order of 2-3% for eutrophication. For acidification, however, the exceedances depend both on the sulphur and nitrogen deposition. Since, no contribution is estimated for sulphur deposition, the contribution to acidification from aircraft will depend non-linearily on the nitrogen deposition. This contribution to acidification will be smaller than 2-3%. This contribution is small but comparable to the contribution of other individual sources over Europe. It is comparable, for example, to the relative contribution of shipping emissions from the North Sea to countries like Luxembourg or Finland (EMEP, 2003, Part III). Nitrogen Dioxide The contribution of NOx emissions from the LTO phases on annual NO2 concentrations are not negligible and are in fact comparable to the contribution of European non- LTO emissions. This is because nitrogen dioxide is a relatively short-lived species and it is largely affected by neighbouring sources. Figure 10 shows how nitrogen oxide emissions from aviation affect NO2 concentrations in Europe. Both LTO and non-LTO emissions contribute with 0.05-2% to surface NO2 concentrations in the vicinity of airports. Away from airport areas, the relative contribution of aviation sources to regional NO2 surface levels is at least an order of magnitude smaller and therefore considered to be negligible. In the vicinity of airports, regional NO2 concentrations are largely affected by NOx LTO emissions. Since a considerable part of the non-LTO NOx emissions are emitted within the atmospheric boundary layer, although above 1000m, non-LTO NOx emissions at climbing phases also affect the NO2 surface concentration levels. This explains partly why the contribution to NO2 surface concentrations is larger for non-LTO emissions above the European area than the contribution of global non-LTO emissions. The other reason is related to the effect of non-linearities in the ozone chemistry. The increase in ozone levels derived from the influence of global non-LTO emissions implies a decrease of the surface NO2 levels. For NOx emissions from aviation over the European area, the derived increase in ozone is not so pronounced and the local increase on NO2 emissions dominates the impact of on surface concentrations. It is important to note that the calculations carried out here with the regional scale model tend to underestimate the observed nitrogen dioxide concentrations by 15-20%. This underestimation is a common feature of the general performance of regional scale models and it is related to the resolution describing the NOx emissions. Higher NO2 concentrations from LTO emissions can be expected from dedicated studies using local scale models with higher spatial resolution.

36

.

30354045505560

Summer avg. dmax

2000

0.020.040.060.100.300.400.500.600.700.80

Diff. summer avg. dmax

0.020.040.060.100.200.300.400.500.600.700.80

Diff. summer avg. dmax Eur.

0.020.030.060.100.200.300.400.500.600.700.80

Diff. summer avg. dmax LTO Figure 5. DAILY OZONE MAXIMUM. Upper left panel shows daily ozone maximum during summer (ppbv). Upper right shows the increase (ppbv) caused by global NOx non-LTO emissions. Lower left panel shows the increase (ppbv) due to the effect of European non-LTO aircraft emission, while the lower right panel shows the effect of European LTO aircraft emissions.

37

45505560657075

Avg 10 highest days

0.020.040.060.100.200.300.400.500.600.700.800.90

Diff. 10 highest days

2000

0.020.040.060.100.200.300.400.500.600.700.800.90

Diff. 10 highest days Eur.

2000

0.020.040.060.100.200.300.400.500.600.700.800.90

Diff. 10 highest days LTO Figure 6. OZONE EPISODES. Upper left shows the average surface ozone concentrations (ppbv) during the 10 days with the highest ozone concentrations over the year. Upper right panel shows the increase (ppbv) caused bye global non-LTO emissions from aircraft, while the lower left panel shows the increase (ppbv) caused bye European non-LTO aircraft emissions and lower right panel shows the increase from European LTO aircraft emissions.

38

5000100001500020000250003500045000

AOT40f

2000

1050

200400600800

10001500

Diff. AOT40f

1050

200400600800

10001500

Diff. AOT40f Eur

1050

200400600800

10001500

Diff. AOT40f LTO Figure 7. VEGETATION EXPOSURE. Upper left shows AOT40f.. Upper right shows the increase in AOT40f caused by global non-LTO emissions. The lower left panel depicts the increase in AOT40f caused by European non-LTO emissions whereas the lower right figure depicts the increase caused by European LTO emissions.

39

250500

10002000300050007500

AOT60

2000

51050

100200300400600

Diff. AOT60

51050

100200300400600

Diff. AOT60 Eur

51050

100200300400600

Diff. AOT60 LTO Figure 8. HEALTH EXPOSURE. Upper left shows AOT60. Upper right shows the increase in AOT60 caused by global non-LTO emission. The lower left panel depicts the increase in AOT60 caused by European non-LTO emissions whereas the lower right figure depicts the increase caused by European LTO emissions.

40

50100200300400500

Dry dep ox. N

2000

0.200.400.701.001.502.00

Percentage diff D. dep. ox.N

2000

0.20.40.71.01.52.0

Percentage diff D. dep ox. N Eur

2000

0.20.40.71.01.52.0

Percentage diff. D. dep. ox. N LTO

2000

Figure 9a. ACIDIFICATION AND EUTROPHICATION, annual mean. Upper left panel shows the dry deposition values for year 2000 ( mg/m2), upper right panel shows the percentage increase (%) due to the effect of global non-LTO emissions, the lower left panel shows the percentage increase (%) in dry deposition caused by European non-LTO emissions over Europe. The lower right panel shows dry depositions from European LTO emissions.

41

50100200300400500

Wet dep ox. N

2000

0.200.400.701.001.502.00

Percentage diff W. dep. ox.N

2000

0.20.40.71.01.52.0

Percentage diff W. dep ox. N Eur

2000

0.20.40.71.01.52.0

Percentage diff. W. dep. ox. N LTO

2000

Figure 9b. ACIDIFICATION AND EUTROPHICATION, annual mean. Upper left panel shows the wet deposition values for year 2000 (mg/m2), upper right panel shows the percentage increase (%) due to the effect of global non-LTO emissions, the lower left panel shows the percentage increase (%) wet deposition caused by European non-LTO emissions. The lower right panel shows the percentage increase (%) in wet depositions from European LTO emissions.

42

Figure 10. NITROGEN DIOXIDE, annual mean. Upper left panel shows NO2 concentrations for year 2000 (µg/m3), upper right panel shows the increase (µg/m3) due to the effect of global non-LTO emissions, the lower left panel shows the increase (µg/m3) in NO2 concentrations caused by European non-LTO emissions over Europe. The lower right panel shows the increase (µg/m3) in NO2 concentrations from European LTO emissions.

43

12358

10

SIA

2000

0.050.100.200.300.500.700.90

percentage diff. SIA

2000

0.050.100.200.300.500.700.90

percentage diff. SIA nonLTO Eur.

2000

0.050.100.200.300.500.700.90

Percentage diff. SIA LTO

2000

Figure 11. SECONDARY INORGANIC AEROSOLS, annual mean. Upper left panel shows SIA concentrations for year 2000 (µg/m3), upper right panel shows the percentage increase (%) due to the effect of global non-LTO emissions, the lower left panel shows the percentage increase (%) in SIA concentrations caused by European non-LTO emissions. The lower right panel shows the percentage increase (%) in SIA concentrations from European LTO emissions.

44

Concentrations of secondary inorganic aerosols Secondary inorganic aerosols (SIA) consist mainly of sulphate-, nitrate- and ammonium containing particles. Aircraft emissions enhance concentrations of SIA mainly through oxidation of the primary pollutant NOx to nitrate which can form particles. There is also a small feedback through atmospheric chemistry, as the levels of oxidants (OH and H2O2) are changed so that oxidation of SO2 to SO4

2- is changed slightly. Figure 11 shows that the levels of SIA at the surface increase by less than 1% due to non-LTO emissions. The emissions over Europe can account for about half of this increase. LTO emissions show a negligible contribution. This study considers only the contribution of aviation to particulate matter in terms of the increased concentrations of ammonium nitrate because all other emissions of precursors gases (SOx, NH3) or primary particles (PM10) were considered to be too small and too uncertain to be included in the calculations. 3.2.5. Future impacts: results for 2015, 2020 and 2050 on the regional impact of non-LTO emissions from aviation

The potential future impacts are addressed through a set of simulations for 2050 using the same meteorological conditions as in the previous runs (year 2000). The emission projections for 2050 are:

• the NASA emission inventory projection for aircraft emission of NOx, and • the SRES A2 scenario for surface anthropogenic emissions for all other gaseous components

(IPCC, 2001). Assessment of the impacts for intermediate years, 2010 and 2020 is done by interpolation according to the scenarios for aircraft NOx emissions used in IPCC (1999), as explained in the next section. The global and the regional models have both been run with the 2050 emission projections (cf. Figure 4). The 2050 boundary concentrations for the regional CTM are again taken from the global CTM. The regional CTM, the EMEP model, has then been used to perform two simulations corresponding to simulations 2 and 4 in Section 3.2.2, but with 2050 emissions and boundary concentrations.

5. Including only the non-LTO emissions from aircraft.

Boundary conditions (BC) from the global simulation with aircraft. 6. No emissions from aircraft.

Boundary conditions (BC) from the global simulation without aircraft. Experiments corresponding to simulations 2 and 4 for the 2000 case (Section 3.2.2), were chosen since non-LTO emissions do affect air quality in Europe while the effect of LTO emissions are shown generally to be less important. Figure 12 shows the calculated increase in summer average daily maximum ozone (upper panel) and the average increase in ozone during the 10 days with the highest daily maximum ozone concentrations at the ground. The increase in surface ozone follows the same pattern as for the 2000 case (ref. Figures 5 and 6). However, the increase of maximum ozone concentration is higher by a factor of about 2.2 in 2050 as compared to 2000, while the aircraft emissions have gone up by a factor of 3.1. This illustrates how the non-linear effects influence the ozone budget, by decreasing the ozone production efficiency as the background NOx levels increase.

45

.

30354045505560

Summer avg. dmax

2050

0.20.40.60.81.01.21.4

Diff. summer avg dmax

2050

0.50.81.11.41.72.02.3

Diff. 10 highest days

2050

Figure 12. Projections for 2050. Upper left panel: daily maximum ozone calculated with 2050 emissions. Upper right panel: Increased average daily ozone maximum during summer (ppbv) at the surface due to global non-LTO emissions from aircraft in 2050. Lower panel: Increase in maximum surface ozone concentrations (ppbv) during the 10 day with highest ozone concentrations over the year due to global non-LTO emissions from aircraft in 2050.

46

However, it should be noted that the SRES A2 scenario represents a 30% increase in surface NOx emissions from OECD countries in Europe, while the current trend (over the last 10 years) in surface NOx emissions in the EU is slightly negative (Vestreng and Klein, 2002). If it turns out that the surface NOx emissions in Europe become lower than given by the A2 scenario, then the relative ozone increases due to the non-LTO emissions can be expected to be higher and closer to relative increases in the emissions from aviation. In addition, it should also be kept in mind that the current trend in emissions from aviation is significantly lower than predicted a few years ago, mainly due to the current international economical and political situation. To what extent this is a more permanent shift (i.e. that it changes peoples travel habits) remains to be seen. Figure 13 shows the increase in the AOT40 index for ozone due to global non-LTO emissions in 2050.The increase is more proportional to the increase in the aircraft emission than for the daily maximum and the 10-day maximum concentrations. This is due to compensating non-linear effects through chemistry and through the definition of the AOT40 index. The increase in the wet and dry deposition of oxidized nitrogen due to the global non-LTO emissions in 2050 is shown in Figure 14. The contribution from non-LTO emissions to the deposition in Western Europe is about twice as high as in 2000 simulations (cf. Figures 9a and 9b), and somewhat lower in Eastern Europe due to larger increase in surface emissions of NOx in this part of Europe in the SRES A2 scenario. The increase in secondary inorganic aerosols (SIA) due to the global non-LTO emissions in 2050 is shown in Figure 15. The pattern is almost exactly equal to the pattern for the 2000 case, with a relative enhancement between 2000 and 2050 by a factor of about 2.2, similar to the absolute enhancement of the ozone concentration changes. For SIA this is due to enhanced background levels caused by increases in surface emissions leading to SIA.

75012501750225027503250

Diff AOT40f nonLTO - no airc.

2050

250500750

12501750

Diff AOT60 nonLTO - no airc.

2050

Figure 13. Increase in AOT40_forest and AOT60 (ppbv hours) due to global non-LTO emissions from aircraft in 2050. The increase in surface concentrations of nitrogen dioxide due to the global non-LTO emissions in 2050 is shown in Figure 16. The contribution is shown in percent and shows a similar contribution as i in 2000 simulations (cf. Figure 10). As explained before, because of the importance of local contributions to NO2 concentrations, we expect the increase of surface concentrations of nitrogen dioxide to be larger due to LTO emissions and European non-LTO emissions in 2050. IPCC (1999, Table 9-19) presents projections of emissions from aircraft based on the IS92 scenarios. The NOx emissions from aviation based on the IS92a scenario is 2.39 Tg(N)/yr in 2050 (10% higher than the NASA 2050 scenario which has been used in this study). Using the 2000 and the 2015

47

projections to interpolate the global NOx emissions from aircraft in 2010 yields 0.93 Tg(N)/yr in 2010, i.e. +31 % compared to 2000. Using the 2015 and the 2025 projections to interpolate the global NOx emissions from aircraft in 2020 yields 1.17 Tg(N)/yr in 2020, i.e. +65 % compared to 2000. Assuming a linear ozone response (i.e. that NOx background does not change significantly which seems reasonable given the observed small decline in NOx surface emissions in Europe), the absolute ozone changes given in Figures 5 and 6 can be scaled up by these factors to give rough estimates for 2010 and 2020. Sensitivity studies reported in IPCC (1999) justify this assumption. Increasing the NOx emissions in the free troposphere from lightning from 5 to 12 Tg(N)/yr, was found to reduce the ozone perturbations caused by aircraft (in 2015) by only about 15%. For the AOT40 index it is more difficult just to scale it up without doing the actual CTM simulations, due to the non-linear behaviour of this index. However, the fact that the increase in AOT40 between 2000 and 2050 (Figures 7 and 13) is quite linear suggests that this can be done also for the AOT40 index

0.20.71.21.72.22.73.2

Percentage diff W.dep ox. N

2000 12 31 12 +6

2050

0.20.71.21.72.22.73.2

Percentage diff D.dep ox. N

2000 12 31 12 +6

2050

Figure 14. Increase (percent) in wet deposition (upper panel) and dry deposition (lower panel) of oxidized nitrogen due to global non-LTO emissions from aircraft in 2050.

48

0.20.50.81.11.41.72.0

Percentage diff SIA

2050

Figure 15. Increase (percent) in secondary inorganic aerosols due to global non-LTO emissions from aircraft in 2050.

Figure 16. Increase (percent) in NO2 concentrations due to global non-LTO emissions from aircraft in 2050.

49

3.3. CONCLUSIONS

The overview Table 9 below compares the effect of non-LTO NOx global emissions, with the effect of non-LTO NOx emissions over Europe (EMEP model domain, see Table 6) and with the effect of LTO NOx emissions. It is shown that global NOx non-LTO emissions affect surface air quality in Europe with a small (2-3% for deposition of oxidised nitrogen, 1% for air concentrations of SIA, nitrogen dioxide and ozone) but significant contribution. Except for nitrogen dioxide, the contribution of non-LTO emissions over the European area represents about half of the global non-LTO emission contribution, while the contribution of LTO emissions from aviation is generally an order of magnitude smaller and therefore considered to be of little significance for European air quality at a regional scale. The contribution of aviation emissions to air quality in Europe listed in the overview table is consistent with results of previous global studies. The share of non-LTO emissions is estimated to be small but comparable to the share of a small European country to depositions and concentrations over Europe. The main difference between a small country contribution and aviation non-LTO contribution is that while a country contribution will be limited in geographical or spatial extent, the contribution from non-LTO aviation is more homogenously distributed over Europe.

Table 9. Overview of the impact of emissions from aviation at regional scale Increase on average air quality indicators over Europe

Non-LTO NOx Global emissions 2000

Non-LTO NOx European area 2000

LTO NOx European area 2000


Summer daily maximum ozone

0.4 – 0.6 ppbv (about 1%)

0.2 -0.4 ppbv Negligible < 0.02 ppbv

0.5-1.4 ppbv

Ozone events

0.6 – 0.8 ppbv 0.3 – 0.4 ppbv Negligible < 0.02 ppbv

0.5-2.0 ppbv

AOT40 forests

400 – 1000 ppbv hours (5-10% increase)

< 400 ppbv hours Negligible <50 ppbv hours

1000 – 3000 ppbv hours

AOT60

Typically 100 ppb hours in south/central Europe

<100 ppbv hours Negligible 250 – 1000 ppb hours in south/central Europe

Deposition of oxidized nitrogen

2-3%

0.5% - 1%

Negligible <0.02 %

1.5-3.5%

Nitrogen Dioxide Vicinity of airports 0.005 -0.01 µg/m3 < 0.5 -1%

Vicinity of airports 0.01 -0.02 µg/m3 1 -2%

Vicinity of airports 0.01 -0.02 µg/m3 1-2 %

Vicinity of airports 0.01-0.08 µg/m3 < 0.5 -1%

SIA (Secondary inorganic aerosols)

0.5 – 1%

< 0.5%

Negligible <0.05%

1 – 2%

Primary PM concentrations

None (not considered)




Deposition of reduced nitrogen





Deposition of sulphur





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4. SUMMARY AND CONCLUSIONS Emissions from aviation Aircraft emissions with an impact on air quality are estimated to be primarily released as nitrogen oxides (NOx) and to a considerably minor degree as carbon monoxide (CO), non-methane hydrocarbons (NMVOC), sulphur dioxide (SO2) and primary particulate matter (PM10). The global emission of NOx from aircraft for the 1990s is estimated to 0.71 Tg(N)/year. This represents a contribution of 2% to the global NOx emissions. For other CO, NMVOC and SO2, estimates of the relative contribution of aircraft emissions to global emissions are an order of magnitude smaller and vary between 0,1% and 0,2%. Aviation is a source of particulate matter. Estimates of PM10 emissions from aviation are uncertain but indicate a very small contribution compared to ground sources (less than 0.001% of the global emissions). Emissions of ammonia from aviation have not been described in the literature. For most compounds, emissions in the non-LTO phase are dominant and constitute over 90% of the total aircraft emissions. The only exceptions are carbon monoxide (CO) and hydrocarbon (NMVOC/HC) emissions where the non-LTO contribution of emissions is about 40 % of the total emission. The fraction of non-LTO to the total emissions may change in the future if the average trip length is changed (longer average trips will imply a larger non-LTO fraction) or if applied technologies affects non-LTO emission differently from LTO-emissions. The share aircraft emissions occurring over Europe in the total non-LTO emissions is estimated to be between 15% and 20% for the different compounds. Aircraft emission estimates from the different reviewed inventories are in good agreement with each other. However, it is important to bear in mind the estimates are partly based on the same data, so that uncertainties may be slightly higher than the range of different results would indicate. Uncertainties may be up to 40 % (EEA 2002). Projections for aircraft emissions are more uncertain and less transparent. In 2015 projections from the different inventory approaches show differences of 14% while the variations in projections for 2050 emissions are larger and up to 40%. Aviation emissions chemistry and transport modelling As part of this study, a dedicated modelling exercise has been set up to evaluate the effect of LTO and non-LTO emissions from aviation on air quality levels over Europe. The analysis focuses on NOx emissions because all other components are expected have only minor contributions to global and European emission levels both in 2000 and in 2050. The study has been carried out for the meteorological conditions of year 2000 and with emission data for year 2000 and projections for 2050. From these, rough estimates for 2010 and 2020 have been derived by interpolation. Impacts of non-LTO emissions in 2000 in Europe The study indicates that NOx non-LTO emissions affect regional air quality at the surface significantly more than LTO emissions. This is the case for all regional air quality indicators analysed here and is a consequence of the predominance of non-LTO emissions (95%) over LTO emissions, the atmospheric vertical exchange between the surface and the free troposphere and of the high efficiency of NOx ozone production at free tropospheric levels. The overview table below compares the effect of non-LTO NOx global emissions, with the effect of non-LTO NOx emissions over Europe and with the effect of LTO NOx emissions. It is shown that global NOx non-LTO emissions affect surface air quality in Europe with a small but significant contribution. The contribution of non-LTO emissions from the European area represents about half of

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the global non-LTO emission contribution, while the contribution of LTO emissions from aviation is generally an order of magnitude smaller and therefore considered to be negligible. It is important to note that the contribution of non-LTO emissions occurring over European territory to air quality levels in Europe (50% of the global effect) is larger than its share of the global non-LTO emissions (only 15%). This indicates that European emission reduction strategies for non-LTO emissions may be effective to improve air quality in Europe. The contribution of aviation emissions to regional air quality in Europe listed in the overview table is consistent with results of previous global studies. The share of non-LTO emissions is estimated to be small (2-3% for deposition of oxidised nitrogen, 1% for air concentrations of SIA, nitrogen dioxide and ozone) but comparable to the share of a small European country to depositions and concentrations over Europe. The main difference between a small country contribution and aviation non-LTO NOx contribution is that while a country contribution will be limited in geographical or spatial extent, the contribution from non-LTO NOx aviation has a wider geographical extension and covers most of Europe.

Overview of the impact of emissions from aviation at regional scale Increase on average air quality indicators over Europe


Non-LTO NOx European area 2000

LTO NOx

European area 2000


Summer daily maximum ozone

0.4 – 0.6 ppbv (about 1%)

0.2 -0.4 ppbv Negligible < 0.02 ppbv

0.5-1.4 ppbv

Ozone events

0.6 – 0.8 ppbv 0.3 – 0.4 ppbv Negligible < 0.02 ppbv

0.5-2.0 ppbv

AOT40 forests

400 – 1000 ppbv hours (5-10% increase)

< 400 ppbv hours Negligible <50 ppbv hours

1000 – 3000 ppbv hours

AOT60

Typically 100 ppbv hours in south/central Europe

<100 ppbv hours Negligible 250 – 1000 ppbv hours in south/central Europe

Deposition of oxidized nitrogen

2-3%

0.5% - 1%

Negligible <0.02 %

1.5-3.5%

Nitrogen Dioxide Vicinity of airports 0.005 -0.01 µg/m3 < 0.5 -1%

Vicinity of airports 0.01 -0.02 µg/m3 1 -2%

Vicinity of airports 0.01 -0.02 µg/m3 1-2 %

Vicinity of airports 0.01-0.08 µg/m3 < 0.5 -1%

SIA (Secondary inorganic aerosols)

0.5 – 1%

< 0.5%

Negligible <0.05%

1 – 2%

Primary PM concentrations

Negligible (not considered)




Deposition of reduced nitrogen





Deposition of sulphur





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Ozone: Global non-LTO NOx emissions from aviation increase the daily averaged maximum ozone at surface by 0.4-0.6 ppbv over Europe. On average, the increase in summer (April to September) ozone at the surface level due to non-LTO global emissions is of the order of 1%. European non-LTO emissions have a smaller impact, about 0.2-0.4 ppbv. The contribution of LTO emissions is negligible. For other indicators for ozone impact, like AOT40 and AOT60, the effect of the non-LTO emissions becomes more significant with increasing ozone levels, so that it contributes with about a 5-10% increase for AOT40 and up to 30% for AOT60. Acidification and eutrophication: The contribution of global non-LTO emissions to deposition of oxidised nitrogen constitutes an increase of the total levels by 2-3%. This contribution is 50% larger for global non-LTO emissions than for European non-LTO emissions only, particularly for wet deposition, which indicates the importance of intercontinental pollution exchange at free tropospheric levels. Non-LTO over Europe contributes with about 0.5-1.5% percent increase on the deposition of oxides nitrogen in Europe. The deposition of oxidised nitrogen from LTO emissions over Europe is below 0.4%. The contribution of aviation non-LTO emissions to eutrophication is the same as its share to total deposition. For acidification, the share of aviation non-LTO emissions will be lower than for eutrophication. This is because acidification depends non-linearly on the nitrogen deposition as is determined both by sulphur and nitrogen depositions from other sources. The share of sulphur emissions from aviation has been estimated to be negligible and therefore has not been included here. Nitrogen dioxide: The contribution of LTO NOx emissions to air concentrations of nitrogen dioxide in the vicinity of airports is not negligible and is in fact comparable to the contribution of European nonLTO emissions. This is because NO2 is a short lived component that is high dependent on the influence of local sources. Higher contribution from LTO and climbing aircraft emissions can be expected from dedicated studies using a higher spatial resolution than the one used in the present study. Secondary inorganic aerosols: With respect to PM concentrations, this study considers only the contribution of aviation in terms of the increased concentrations of secondary inorganic aerosols. This involves primarily ammonium nitrate from NOx non-LTO and LTO emissions because neither ammonia nor sulphur dioxide emissions from aviation were included in the calculations. The European and global non-LTO emissions from aviation contribute with about half and half to the increase in the concentrations of secondary inorganic aerosols (SIA) at the surface layer in Europe. This increase represents ~1% of the SIA concentrations and is about one order of magnitude larger than the contribution from LTO NOx emissions. Emissions of primary PM were not included in the calculation because these emissions were estimated to be of negligible significance compared to other sources. Impacts of non-LTO emissions in 2010, 2020 and 2050 in Europe The projections for 2050 and derived interpolated values for 2010 and 2020 are conservative estimates of the expected impact of aviation emissions in future scenarios. Only the effect of non-LTO emissions from aviation has been considered because the effect of LTO emissions is estimated to be negligible except for the case of local NO2 levels. The projection estimates use NASA projections for aviation and the SRES A2 scenario for other European emissions. This implies high background NOx concentrations that decreases ozone production efficiency and thus provides a lower estimate of the impact of NOx non-LTO emissions in 2050. It is expected that surface NOx emissions will be lower in 2050 than predicted by the SRES A2 scenario and therefore we can expect the impact of non-LTO emissions from aviation to be larger in 2050 than indicated in the overview table.

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Need for further studies This study was completed before relevant new information on emission projections from aviation was available for evaluation. The projection estimates for 2010, 2020 and 2050 presented here are all conservative estimates that show the lowest expected impact from aircraft emissions on surface air quality. The results vary depending on the scenarios selected for 2050 according to differences in assumptions about future technology and traffic volume. Estimates of impact of future aircraft emissions should consider different background concentrations into which emissions will be injected (less conservative than the SRES A2 scenario) and different scenarios for future aviation. It is recommended to analyse the effect for future scenarios (CAEP/6, EUROCONTROL, AERO2K, CONSAVE 2050) when these are available. The recommendation is to study further the effect of control options to reduce NOx emissions from the global aviation, in particular concerning the non-LTO cycle. The study should also include aircraft emission projection information in particular for carbon monoxide (CO) and non methane volatile organic compounds (NMVOC). It is expected that for CO and NMVOC, the impact of emissions on surface air quality from the LTO emission cycle can be larger than for the non-LTO phases. This is because CO and NMVOC are formed at the low power settings or idle phases that occur mainly during the LTO cycle, so that emissions at LTO cycle are about 60% of the total emissions. In areas with low NOx concentration levels, where ozone formation is VOC controlled, the effect of emissions CO and NMVOC from LTO may be more important than the effect of non-LTO emissions for the ozone surface levels. It is also recommended to investigate further possible measures to reduce global non-LTO emissions of air quality components in relation with climate change strategies. Non-LTO emissions from aviation have larger potential impact in climate related issues than in air quality problems and therefore synergies should be analysed. European aircraft emissions have been understood in this study as emissions above the European regional domain. The share of European emissions used in this way is estimated to 15% -20% of the global aircraft emissions. Other definitions of what the European share of emissions is may result in different estimates. Calculations based on available statistics on fuel use and traffic demand indicate a significantly higher share of the European emissions from aircraft. As more complete data on the European share of emission from aviation becomes available, it is recommended to consider to what extent European measures can be proved effective to improve surface air quality and deposition levels in Europe.

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6. APPENDIX: ACRONYMS AND ABBREVIATIONS

ACARE Advisory Council on Aeronautics Research in Europe ANCAT Abatement of Noises Caused by Air Transport ATM Air Traffic Management System CAEP Committee on Aviation Environmental protection. CEPMEIP Co-ordinated European Programme on Particulate Matter Emission Inventories. CLRTAP Convention on Long Range Transport of Air Pollution in Europe CNS Communication Navigation Surveillance CORSAIRE Coordination of Research for the Study of Aircraft Impact on the Environment COST European Co-operation in the Field of Scientific Research CTM Chemical Transport Modell DAC Dual Annular Combustor DLR German Aerospace Center ECMWF European Center for Medium Range Weather Forecast EEA European Environmental Agency. EMEP European Monitoring and Evaluation Program EDGAR Emission Database for Global Atmospheric Research EUROCONTROL European Organisation for Safety and Navigation FESG Forecast and Economics Sub-Group GAO United States General Accounting Office. HC Hydrocarbons HFC Hydrofluorocarbon HIRLAM High Resolution Limited Area Model ICAO International Civil Aviation Organization IPCC Intergovernmental Panel on Climate Change LTO Landing and Take-Off MEET Methodologies for Estimating Air Pollutant Emissions from Transport NASA National Aeronautics and Space Administration NEC National Emission Ceiling Directive NESCAUM Northeast States for Coordinated Air Use Management NMVOC Non Methane Volatile Organic Carbon PAN Peroxyacetylnitrate PBL Planetary Boundary Layer PFC Polyflouocarbons PM Particulate Matter ppbv Parts per billion by volume ppmv Parts per million by volume RCEP Royal Commission on Environmental Pollution RF Radiative Forcing RVSM Reduced Vertical Separation Minimum SIA Secondary Inorganic Aerosols SRES Special Report on Emission Scenarios STAR21 Strategic Aerospace Review for the 21st century UNECE United Nations Economic Commission for Europe UNEP United Nations Environmental Program UV Ultraviolett radiation WMO World Meteorological Organization

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