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QUESTIONS

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!

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QUESTIONS

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  1. QUESTIONS • Is hexane more or less reactive with OH than propane? • Is pentene or isoprene more reactive with OH?

  2. LARGE SUPPLY OF BIOGENIC VOCs – unrecognized until the 1990s Switches polluted areas in U.S. from NOx-saturated to NOx-limited regime! recognized in Revised Clean Air Act of 1999 Anthropogenic VOCs Isoprene (biogenic VOC) Jacob et al., [1993] Isoprene (C5H8) and monoterpenes (C10H16) are oxidized by OH, O3 and NO3 (generally analogous to alkene rxn)  secondary organic aerosol (SOA)

  3. LATEST INVENTORIES OF BIOGENIC vs. ANTHROPOGENIC VOCs …notice difference in scale! Millet et al. [2007]

  4. GLOBAL DISTRIBUTION OF ISOPRENE EMISSIONS E = f (T, h) MEGAN biogenic emission model (Guenther et al., 2006)

  5. CONSTRAINT ON VOC EMISSIONS FROM SPACE OBSERVATIONS OF FORMALDEHYDE GOME satellite observations (July 1996) 2.5x1016 molecules cm-2 2 1.5 1 detection limit 0.5 South Atlantic Anomaly (disregard) 0 -0.5 High values are associated with biogenic emissions (eastern US), anthropogenic emissions (China), fires (Africa, Siberia)

  6. SIMULATED SENSITIVITY OF SURFACE OZONETO EMISSION CONTROLS U.S is NOx-limited! Jacob et al., [1993b]

  7. U.S. GROWTH MEASURES (2008)

  8. U.S. EMISSIONS OF OZONE PRECURSORSand trends over past 20 years • Vehicles • Fires • Fuel combustion • vehicles • power plants Down 40% Flat/down Anthropogenic VOCs Isoprene (biogenic VOC) • Fuel combustion & transport • Solvents Vegetation Flat Down 30%

  9. OZONE TRENDS IN U.S. http://www.epa.gov/airtrends/ National trend Fort Collins trend

  10. TREND IN 4th-HIGHEST 8-HOUR OZONE,2004-2006 vs 1990-1992

  11. DEPENDENCE OF OZONE PRODUCTION ON NOx AND HYDROCARBONS NET: RH + 4O2 R’CHO + 2O3 + H2O O3 HOxfamily NO RO2 RO 5 RH O2 4 6 PHOx 7 O3 OH HO2 NO NO2, M 9 8 HNO3 O3 H2O2 “NOx- saturated” or “hydrocarbon-limited” regime “NOx-limited” regime

  12. ALTHOUGH THE O3 PRODUCTION RATE IS ~ [NOx],THE TOTAL O3 PRODUCED IS HYDROCARBON-DEPENDENTAND [O3] = f(ENOx) IS STRONGLY NONLINEAR P(O3) L(NOx) HO2,RO2,O3 OH, O3 NO NO2 HNO3 hv Emission Deposition Define ozone production efficiency (OPE) as the total number of O3 molecules produced per unit NOx emitted. Assuming NOx steady state, efficient HOx cycling, and loss of NO2 by reaction with OH: OPE m as NOxk e strong nonlinearity

  13. 1999-2004 NOx EMISSION REDUCTIONSAND SIMULATED EFFECTS ON SURFACE OZONE 50% decrease in power plant emissions 20% decrease in total U.S. emissions Hudman et al. [2008]

  14. TRENDS IN 4th-HIGHEST 8-HOUR OZONEAT NATIONAL PARKS, 1992-2001 [EPA, 2003]

  15. OBSERVED TREND IN OZONE BACKGROUND OVER CALIFORNIA IN SPRING SUGGESTS 10-15 ppbv INCREASEOVER PAST 20 YEARS Trend: 0.5-0.8 ppbv yr-1 Jaffe et al. [2003] Background: concentration that would be present in absence of local anthropogenic emissions

  16. RISING OZONE BACKGROUND IN EUROPE Hohenpeissenberg/ Payerne 3-5 km polluted background Naja et al. [2003] Changes in anthrop. NOx emissions Mace Head, 1987-2004 [Simmonds et al., 2004]

  17. HEMISPHERIC OZONE POLLUTION:IMPLICATIONS OF ENHANCED OZONE BACKGROUND FOR MEETING AIR QUALITY STANDARDS (AQS) Europe AQS (8-h avg.) Europe AQS (seasonal) U.S. AQS (8-h avg.) U.S. AQS (1-h avg.) Was here until 2008! 0 20 40 60 80 100 120 ppbv Preindustrial ozone background Present-day ozone background at northern midlatitudes

  18. GLOBAL OZONE BACKGROUND:METHANE AND NOx ARE THE LIMITING PRECURSORS Sensitivity of global tropospheric ozone inventory (Tg) to 50% global reductions in anthropogenic precursor emissions GEOS-Chem model [Fiore et al., 2002] Anthropogenic methane enhances surface ozone by 4-6 ppbv worldwide

  19. PROJECTIONS OF GLOBAL NOx EMISSIONS Anthropogenic NOx emissions [IPCC, 2001] 2000 “Optimistic” IPCC scenario: OECD, U.S. m20%, Asia k 50% 2020 109 atoms N cm-2 s-1

  20. EFFECT OF INCREASING SIBERIAN FOREST FIRES ON SUMMER SURFACE OZONE IN PACIFIC NORTHWEST GEOS-Chem ozone enhancements Observations Siberian fires Ozone Mean summer 2003 enhancement of 5-9 ppbv (9-17 ppbv in events) Jaffe et al. [2004]

  21. Probability of max 8-h O3 > 84 ppbv vs. daily max. T EFFECT OF CLIMATE CHANGE ON OZONE AIR QUALITY Ozone exceedances of 90 ppbv, summer 2003 Lin et al. [Atm. Env. 2001] • Correlation of high ozone with temperature is driven by • stagnation, (2) biogenic hydrocarbon emissions, (3) chemistry

  22. EFFECT OF CLIMATE CHANGE ON REGIONAL STAGNATION GISS GCM simulations for 2050 vs. present-day climate using pollution tracers with constant emissions weather map illustrating cyclonic ventilation of the eastern U.S. 2045-2052 summer 1995-2002 Pollution episodes double in duration in 2050 due to decreasing frequency of cyclones ventilating the eastern U.S; expected result of greenhouse warming. Mickley et al. [2004]

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