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 NO x -saturated to NO x -limited regime! recognized in Revised Clean Air Act of 1999 Isoprene (C 5 H 8 ) and monoterpenes (C 10 H 16 ) are oxidized by OH, O 3 and NO 3 (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 x10 16 molecules cm -2 South Atlantic Anomaly (disregard) detection limit GOME satellite observations (July 1996) High values are associated with biogenic emissions (eastern US), anthropogenic emissions (China), fires (Africa, Siberia)

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

U.S. GROWTH MEASURES (2008)

U.S. EMISSIONS OF OZONE PRECURSORS and 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

OZONE TRENDS IN U.S. National trend Fort Collins trend

TREND IN 4 th -HIGHEST 8-HOUR OZONE, vs

DEPENDENCE OF OZONE PRODUCTION ON NO x AND HYDROCARBONS HO x family OH RO 2 RO HO 2 HNO 3 H2O2H2O2 O3O3 O3O3 O3O3 P HOx “NO x - saturated” or “hydrocarbon-limited” regime “NO x -limited” regime RH NO O2O2 NO 2, M NET: RH + 4O 2  R’CHO + 2O 3 + H 2 O

ALTHOUGH THE O 3 PRODUCTION RATE IS ~ [NO x ], THE TOTAL O 3 PRODUCED IS HYDROCARBON-DEPENDENT AND [O 3 ] = f(E NOx ) IS STRONGLY NONLINEAR NO NO 2 HNO 3 hv HO 2,RO 2,O 3 OH, O 3 P(O 3 ) L(NO x ) EmissionDeposition Assuming NO x steady state, efficient HO x cycling, and loss of NO 2 by reaction with OH: OPE  as NO x  strong nonlinearity Define ozone production efficiency (OPE) as the total number of O 3 molecules produced per unit NO x emitted.

NO x EMISSION REDUCTIONS AND SIMULATED EFFECTS ON SURFACE OZONE Hudman et al. [2008] 50% decrease in power plant emissions 20% decrease in total U.S. emissions

TRENDS IN 4 th -HIGHEST 8-HOUR OZONE AT NATIONAL PARKS, [EPA, 2003]

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

RISING OZONE BACKGROUND IN EUROPE 3-5 km polluted background Naja et al. [2003] Hohenpeissenberg/ Payerne Mace Head, [Simmonds et al., 2004] Changes in anthrop. NO x emissions

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

GLOBAL OZONE BACKGROUND: METHANE AND NO x ARE THE LIMITING PRECURSORS 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 reductions in anthropogenic precursor emissions

PROJECTIONS OF GLOBAL NO x EMISSIONS 10 9 atoms N cm -2 s -1 Anthropogenic NO x emissions [IPCC, 2001] “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 enhancement of 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 QUALITY Probability of max 8-h O 3 > 84 ppbv vs. 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 GISS GCM simulations for 2050 vs. present-day climate using pollution tracers with constant emissions Mickley et al. [2004] summer weather map illustrating cyclonic ventilation of the eastern U.S.