questions 1.is hexane more or less reactive with oh than propane? 2.is pentene or isoprene more...
TRANSCRIPT
QUESTIONS
1. Is hexane more or less reactive with OH than propane?
2. Is pentene or isoprene more reactive with OH?
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)
LATEST INVENTORIES OF BIOGENIC vs. ANTHROPOGENIC VOCs
Millet et al. [2007]
…notice difference in scale!
GLOBAL DISTRIBUTION OF ISOPRENE EMISSIONS
MEGAN biogenic emission model (Guenther et al., 2006)
E = f (T, h)
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)
SIMULATED SENSITIVITY OF SURFACE OZONETO EMISSION CONTROLS
U.S is NOx-limited!
Jacob et al., [1993b]
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
DEPENDENCE OF OZONE PRODUCTION ON NOx AND HYDROCARBONS
HOxfamily
OH
RO2 RO
HO2
HNO3 H2O2O3
O3
O3
PHOx
4
5
67
89
1/ 23 7
8
( ) 2 ( ) [ ]HOxPP O k NO
k4
39 2
2 [ ]( )
[ ][ ]HOxk P RH
P Ok NO M
“NOx- saturated” or“hydrocarbon-limited” regime
“NOx-limited” regime
RH
NO
O2
NO
NO2, M
NET: RH + 4O2 R’CHO + 2O3 + H2O
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 RH
L 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.
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
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
RISING OZONE BACKGROUND IN EUROPE
3-5 km
polluted
backgroundNaja et al. [2003]
Hohenpeissenberg/Payerne
Mace Head, 1987-2004 [Simmonds et al., 2004]
Changes in anthrop. NOx emissions
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!
GLOBAL OZONE BACKGROUND:METHANE AND NOx ARE THE LIMITING PRECURSORS
240
250
260
270
280
290
300
310
320
3301995 base case
50% methane
50% NOx
50% NMVOCs
50%NOx+NMVOCs
50% 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
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%
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
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
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.