questions
DESCRIPTION
QUESTIONS. Is hexane more or less reactive with OH than propane? Is pentene or isoprene more reactive with OH?. LARGE SUPPLY OF BIOGENIC VOCs – unrecognized until the 1990s. Switches polluted areas in U.S. from NO x -saturated to NO x -limited regime! - PowerPoint PPT PresentationTRANSCRIPT
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QUESTIONS
1. Is hexane more or less reactive with OH than propane?
2. Is pentene or isoprene more reactive with OH?
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LARGE SUPPLY OF BIOGENIC VOCs – unrecognized until the 1990s
Isoprene (biogenic VOC)Anthropogenic VOCs
Jacob et al., [1993]
Switches polluted areas in U.S. from NOx-saturated to NOx-limited regime!recognized in Revised Clean Air Act of 1999
Isoprene (C5H8) and monoterpenes (C10H16) are oxidized by OH, O3 and NO3
(generally analogous to alkene rxn) secondary organic aerosol (SOA)
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LATEST INVENTORIES OF BIOGENIC vs. ANTHROPOGENIC VOCs
Millet et al. [2007]
…notice difference in scale!
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GLOBAL DISTRIBUTION OF ISOPRENE EMISSIONS
MEGAN biogenic emission model (Guenther et al., 2006)
E = f (T, h)
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CONSTRAINT ON VOC EMISSIONS FROM SPACE OBSERVATIONS OF FORMALDEHYDE
-0.5
0
0.5
1
1.5
2
2.5x1016
moleculescm-2
SouthAtlanticAnomaly(disregard)
detectionlimit
GOME satellite observations (July 1996)
High values are associated with biogenic emissions (eastern US), anthropogenic emissions (China), fires (Africa, Siberia)
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SIMULATED SENSITIVITY OF SURFACE OZONETO EMISSION CONTROLS
U.S is NOx-limited!
Jacob et al., [1993b]
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U.S. GROWTH MEASURES (2008)
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U.S. EMISSIONS OF OZONE PRECURSORSand trends over past 20 years
Anthropogenic VOCs
Fuel combustion• vehicles• power plants
•Fuel combustion & transport• Solvents
• Vehicles• Fires
Isoprene (biogenic VOC)
Vegetation
Flat/down
Down 30%
Down 40%
Flat
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OZONE TRENDS IN U.S. http://www.epa.gov/airtrends/
National trend
Fort Collins trend
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TREND IN 4th-HIGHEST 8-HOUR OZONE,2004-2006 vs 1990-1992
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DEPENDENCE OF OZONE PRODUCTION ON NOx AND HYDROCARBONS
HOxfamily
OH
RO2 RO
HO2
HNO3 H2O2O3
O3
O3
PHOx
45
67
89
1/ 23 7
8
( ) 2 ( ) [ ]HOxPP O k NOk
43
9 2
2 [ ]( )
[ ][ ]HOxk P RH
P Ok NO M
“NOx- saturated” or“hydrocarbon-limited” regime
“NOx-limited” regime
RH
NO
O2
NONO2, M
NET: RH + 4O2 R’CHO + 2O3 + H2O
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ALTHOUGH THE O3 PRODUCTION RATE IS ~ [NOx],THE TOTAL O3 PRODUCED IS HYDROCARBON-DEPENDENT
AND [O3] = f(ENOx) IS STRONGLY NONLINEAR
NO NO2 HNO3hv
HO2,RO2,O3 OH, O3
P(O3) L(NOx)
3 7 2 4
9 2 9 2
( ) 2 [ ][ ] 2 [ ]( ) [ ][ ] [ ]
OPE = x
P O k HO NO k RHL NO k NO OH k NO
Emission Deposition
Assuming NOx steady state, efficient HOx cycling, and loss of NO2 by reaction with OH:
OPE as NOx strong nonlinearity
Define ozone production efficiency (OPE) as the total number of O3 molecules produced per unit NOx emitted.
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1999-2004 NOx EMISSION REDUCTIONSAND SIMULATED EFFECTS ON SURFACE OZONE
Hudman et al. [2008]50% decrease in power plant emissions20% decrease in total U.S. emissions
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TRENDS IN 4th-HIGHEST 8-HOUR OZONEAT NATIONAL PARKS, 1992-2001 [EPA, 2003]
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OBSERVED TREND IN OZONE BACKGROUND OVER CALIFORNIA IN SPRING SUGGESTS 10-15 ppbv INCREASE
OVER PAST 20 YEARS
Trend: 0.5-0.8 ppbv yr-1Jaffe et al. [2003]
Background: concentration that would be present in absence of localanthropogenic emissions
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RISING OZONE BACKGROUND IN EUROPE
3-5 kmpolluted
backgroundNaja et al. [2003]
Hohenpeissenberg/Payerne
Mace Head, 1987-2004 [Simmonds et al., 2004]
Changes in anthrop. NOx emissions
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HEMISPHERIC OZONE POLLUTION:IMPLICATIONS OF ENHANCED OZONE BACKGROUND
FOR MEETING AIR QUALITY STANDARDS (AQS)
0 20 40 60 80 100 120 ppbv
Europe AQS(seasonal)
U.S. AQS(8-h avg.)
U.S. AQS(1-h avg.)
Preindustrialozone
background
Present-day ozone background at
northern midlatitudes
Europe AQS (8-h avg.)
Was here until 2008!
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GLOBAL OZONE BACKGROUND:METHANE AND NOx ARE THE LIMITING PRECURSORS
240250260270280290300310320330
1995 base case
50% methane
50% NOx
50% NMVOCs
50%NOx+NMVOCs50% CO
50% all
natural
GEOS-Chem model [Fiore et al., 2002]
Anthropogenic methane enhances surface ozone by 4-6 ppbv worldwide
Sensitivity of global tropospheric ozone inventory (Tg) to 50% global reductionsin anthropogenic precursor emissions
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PROJECTIONS OF GLOBAL NOx EMISSIONS
109 atoms N cm-2 s-1
AnthropogenicNOx emissions[IPCC, 2001]
2000
2020
“Optimistic” IPCC scenario: OECD, U.S. 20%, Asia 50%
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EFFECT OF INCREASING SIBERIAN FOREST FIRES ON SUMMER SURFACE OZONE IN PACIFIC NORTHWEST
Mean summer 2003 enhancementof 5-9 ppbv (9-17 ppbv in events)
Jaffe et al. [2004]
Observations GEOS-Chem ozone enhancements
Siberian fires
Ozone
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EFFECT OF CLIMATE CHANGE ON OZONE AIR QUALITYProbability of max 8-h O3 > 84 ppbvvs. daily max. T
Lin et al. [Atm. Env. 2001]
Correlation of high ozone with temperature is driven by(1) stagnation, (2) biogenic hydrocarbon emissions, (3) chemistry
Ozone exceedances of 90 ppbv,summer 2003
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EFFECT OF CLIMATE CHANGE ON REGIONAL STAGNATION
Pollution episodes double in duration in 2050 due to decreasing frequency of cyclones ventilating the eastern U.S; expected result of greenhouse warming.
2045-2052
1995-2002
GISS GCM simulations for 2050 vs. present-day climate using pollution tracers with constant emissions
Mickley et al. [2004]
summer
weather map illustratingcyclonic ventilation of the eastern U.S.