dmug 2016 - michel vedrenne, ricardo energy & environment

The development of the Streamlined-PCM as

a tool for screening the impact of road-traffic

policy actions on NO2 concentrations

Dr. Michel Vedrenne

DMUG 16, London – 19th April 2016

2© Ricardo-AEA Ltd Ricardo Energy & Environment in Confidence

• The assessment of the effectiveness of emission abatement measures is essential for informing

policy making. The objective is to select measures with the highest mitigation potential at the

lowest possible cost.

• The Pollution Climate Mapping (PCM) model provides support to DEFRA in selecting those

measures; however it requires several weeks to carry out the full emissions calculations,

emissions mapping and concentration modelling required to test the effect of measures.

• In order to make well-informed decisions in a shorter timeframe, DEFRA required a simplified

version of the PCM to model a range of road-traffic scenarios.

• The Streamlined PCM has been built as an approximation of the full PCM model using data from

the National Atmospheric Emissions Inventory (NAEI). The results of the tool have a base which is

consistent with the compliance assessment and baseline projections of the full PCM model.

• It has a number of limitations compared to the full PCM model and it is not intended to be a

substitute. Furthermore, the Streamlined PCM requires data produced by the full PCM so it is not

an independent model. Streamlined PCM should be regarded as a screening tool.

Background and model purpose

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• The Streamlined PCM is a tool that enables the quantification of the effect of measures applied to

different aspects of road traffic on the emissions of nitrogen oxides (NOx) and the annual mean

concentration of nitrogen dioxide (NO2).

• The Streamlined PCM has the capacity to assess the impact of measures applied at different

spatial scales including national, local authority, specific geographic areas or the individual road

level

• The tool combines a simplified road traffic emissions model that relies on the National Atmospheric

Emission Inventory (NAEI) for emissions and a parameterisation of the Pollution and Climate

Mapping (PCM) model for ambient concentrations.

• According to the specific abatement measures, the relevant activity variables, fleet compositions

and emission factors are combined to calculate NOx emissions and variation ratios with respect to

a reference scenario.

• The estimation of NOx emissions is carried out for 18,346 road links in 406 local authorities of the

United Kingdom and the change in NO2 concentrations for 9,336 roads for which compliance with

Directive 2008/50/EC is assessed.

Description of the Streamlined PCM

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The technical report of the Streamlined PCM was published

by DEFRA on the 26th November 2015. It is available from

the UK-Air website:

https://uk-air.defra.gov.uk/library/reports?report_id=882

Description of the Streamlined PCM

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https://uk-air.defra.gov.uk/library/reports?report_id=882


The Streamlined PCM tool estimates the effect of NO2 abatement measures to be assessed by comparing a

scenario against a baseline. The baseline corresponds to a fully-characterised reference situation of

emissions. Any additional measure or set of measures beyond those already included in the baseline will

correspond to a scenario.

To characterise the effect of any measure with the Streamlined PCM, it should be modelled as a set

of variations (fi) with respect of the baseline scenario for one or more of the following variables (Vi):

• Activity variables (flows/veh·km by vehicle and fuel type – annual average daily flows).

• Fleet composition variables (fleet mix by vehicle and fuel type – in terms of Euro standards).

• Petrol-to-diesel fuel split.

• Emission factors, including the possibility of changing conformity factors.

𝑓𝑖 =𝑉𝑠𝑐𝑒𝑛𝑎𝑟𝑖𝑜 − 𝑉𝑏𝑎𝑠𝑒𝑙𝑖𝑛𝑒

𝑉𝑏𝑎𝑠𝑒𝑙𝑖𝑛𝑒

The formulation of the adjustment factors (fi) within the framework of the Streamlined PCM defines

measures that seek to reduce the impact of the relevant variables are negative, while those that aim

to increase them are positive. Translating a measure in terms of a set of adjustment factors is a task

that requires careful identification of the degree to which variables change.

Design principles of the Streamlined PCM

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Structure of the Streamlined PCM

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fF

fC

fEF

Flow

Database

Composition

Database

EF

Database

Cars

Buses

Coaches

HGVs

Motorc.

LGVs

Pre Euro

Euro 1

Euro 2

Euro 4

Euro 3

Euro 5

Euro 6

Petrol Diesel

Hybrid

Baseline

Scenario(s)

Reduction %

Baseline

Scenario(s)

Reduction

NO2 LV Comp.

Emissions

Concentrations

Roads

(Census)

Local

Authorities

Streamlined PCM

Adjustment

Factors

Users

Compliance

Measure Emission Reduction

Flowchart of the spreadsheets of the Streamlined PCM

Mapping

NAEI


Structure of the Streamlined PCM (Emissions Module)

The Streamlined PCM contains information on the different road-traffic variables that are likely of

being affected by a given abatement measure, which then combine to estimate the NOx emissions of

road traffic. All these variables are sourced directly from the NAEI or the PCM data and are referred

to 2020.

• Vehicle types. Passenger cars (petrol and diesel), LGVs (small and large, petrol and diesel),

Buses, Coaches, Rigid HGVs, Articulated HGVs, Motorcycles and Mopeds.

• Emission factors. Emission factors and speed-dependent functions from COPERT (v.4.11) are

included in the tool, taking into account the engine size/weight of the vehicle, and for buses and

coaches the load and the slope of the roads (30 road types). Fractions of primary NO2 for each of

the considered vehicles and fuel types are also provided.

• Fleet composition. Euro standard composition in terms of vehicle-kilometres for the different

vehicle types and road types. Compositions are available for two types of locations: London and

the rest of the UK and for three types of roads: motorways, urban roads and rural roads.

• Activity variables. Traffic counts for the considered vehicle types in the form of annual average

daily flows (AADFs) for 18,346 georeferenced roads projected to 2020 using the NAEI projections.

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Structure of the Streamlined PCM (Concentration module)

The Streamlined PCM is also able to estimate the annual mean

concentrations of NO2 as a function of the variation in the NOx emissions

for 9,336 roads. The estimation of concentrations is made through a

parameterisation of the results of the full PCM model, which combines the

following variables :

• Background road traffic area source (Brdarea) – NOx concentration

(μg/m3).

• Background non-road tr. area source (Bnondrarea) – NOx concentration

(μg/m3).

• Background point source (Bpoints) – NOx concentration (μg/m3).

• Background rural (Brural) – NOx concentration (μg/m3).

• Roadside increment – NOx concentration (μg/m3).

• Background local oxidant from road traffic area sources

(Brdarealocalolx – ppb).

• Background local oxidant non-road traffic sources (Bnonrdarealocalox –

ppb).

• Roadside increment local oxidant (Rlocalox – ppb).

• Regional oxidant (Regionalox – ppb).

NO2 roads 2013

NO2 back. 2013

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Appearance of the Streamlined PCM

Application

Geography

Tool

Controls

Adjustment Factor Tables

(to be populated by user)

Other

Controls I/O Tabs

Microsoft Excel® frontend of the Streamlined PCM

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Performance comparison with full PCM

The Streamlined PCM calculates roadside concentrations only; the full PCM model calculates both

roadside and background concentrations. It can take into account the specific changes in emissions of

minor roads and cold starts on backgrounds. The contribution of road transport area sources is scaled

using the proportional change at the roadside in Streamlined PCM. The contribution of non-road transport

sources remains unchanged.

Results from the Streamlined PCM have been compared with the full PCM model for 4 clean air zone

(CAZ) type scenarios in 2020. The mean differences between the two models along with the 5th, 25th, 50th,

75th and 95th percentiles of the differences are provided below (in μg/m3).

The differences between both models range from 0.15-0.25 μg/m3 across the 4 CAZ types. As expected,

differences and limitations between the two models exist, but the results from both models are very close.

The Streamlined PCM is producing larger changes than the full PCM model.

CAZ Type A B C D

Mean -0.15 -0.20 -0.25 -0.16

P5 -0.67 -0.71 -0.73 -0.64

P25 -0.18 -0.24 -0.29 -0.18

P50 -0.06 -0.11 -0.16 -0.09

P75 0.00 -0.04 -0.08 -0.03

P95 0.12 0.07 -0.02 0.14

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Demonstration of the Streamlined PCM

“What is the effect of switching diesel cars for Euro 6 petrol cars in the roads of Norwich in 2020?”*

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Modelling assumptions

• Two change percentages of diesel

vehicles are modelled: 20% and 50%.

• The measure will apply exclusively to the

roads considered by the Streamlined PCM

in the Norwich District.

• The composition specified in Streamlined

PCM for a non-London area in 2020

applies to all the considered roads in the

Norwich District.

• Variables to be affected in Streamlined

PCM: fleet compositions and diesel/petrol

split for passenger cars.

• Effects on minor roads, neighbouring

roads, and cold starts are not considered.

• The effects of the measure will be

noticeable for all the roads in Norwich. The

measure does not affect flows, speeds or

other variables.

Fleet compositions pre- and post-measures (2020)

*This is a hypothetical example for the purposes of demonstrating the

model, it was not commissioned by Defra and it does not reflect Defra’s

thinking.


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Baseline NOx emissions in Norwich District (2020) – [t/yr]*Note: the colour map is different to the one used in PCM official reports for

illustrative purposes only.


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Baseline NO2 annual means in Norwich District (2020) – [μg/m3]*Note: the colour map is different to the one used in PCM official reports for

illustrative purposes only.


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20% diesel cars to Euro 6 petrol – [t/yr] 50% diesel cars to Euro 6 petrol – [t/yr]

NOx Emissions in Norwich District (2020) 20% change 50% change

Emissions after measures 71.3 t/yr 60.4 t/yr

Emission reduction 7.3 t/yr 18.2 t/yr

Reduction percentage 9.27% 23.18%


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20% diesel cars to Euro 6 petrol – [μg/m3] 50% diesel cars to Euro 6 petrol – [μg/m3]

Roadside NO2 Ann. Mean in Norwich District (2020) 20% change 50% change

Maximum annual mean after measures 25.8 μg/m3 23.3 μg/m3

Maximum annual mean reduction 1.5 μg/m3 4.0 μg/m3

Reduction percentage 5.8% 14.6%


Streamlined PCM is …

• A national-level screening tool based on the full PCM model that estimates the effect of

road-transport measures on NOx emissions and NO2 concentrations.

• A resource used by DEFRA for the quick investigation of the effectiveness of mitigation

measures with regards to compliance with Directive 2008/50/EC.

• Comparable results with the full PCM model for road transport measures.

Streamlined PCM is not ...

• A substitute or an independent model from the Pollution Climate Mapping model.

• An alternative to national, regional or local air quality modelling.

• An air quality model in itself.

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Conclusions

Dr. Michel Vedrenne

30 Eastbourne Terrace

W2 6LA London

United Kingdom

[email protected]