2. REGIONAL/GLOBAL INTERACTIONS IN ATMOSPHERIC CHEMISTRY Greenhouse gases Halocarbons Ozone Aerosols Acids Nutrients Toxics SOURCE CONTINENT REGIONAL ISSUES: - Surface air quality - Ecosystems GLOBAL ISSUES: - Climate change - Ozone layer - Oxidizing power GLOBAL ATMOSPHERE

3. TROPOSPHERIC OZONE AND AEROSOLS MAKE LARGE AND INHOMOGENEOUS CONTRIBUTIONS TO RADIATIVE FORCING IPCC 2001 contribution from Harvard/GISS/Caltech/UCI unified aerosol-chemistry-climate model (CACTUS)

4. 1800-2000 radiative forcing from tropospheric ozone is less well constrained than implied by IPCC 2001 report Standard preindustrial simulation: F = 0.44 W m -2 “Adjusted” preindustrial simulation (lightning and soil NOx decreased, biogenic hydrocarbons increased): F = 0.80 W m -2 [Mickley et al., 2001]

5. Ozone+sulfate radiative forcings, 1800-2000 (CACTUS model) Yearly mean values [Mickley et al., 1999]

6. INTERCONTINENTAL INFLUENCE ON SURFACE OZONE: How much does it contribute to ozone pollution? NO x Hydrocarbons Ozone PAN Boundary layer (0-2.5 km) Free troposphere lightning NO x Stratosphere Ozone NO x Hydrocarbons Ozone PAN Chemical loss Deposition CONTINENT 1 CONTINENT 2OCEAN

7. Ozone in U.S. surface air in summer includes a 20-40 ppbv background produced outside the U.S. boundary layer Regional pollution coordinate Ozone Background (“clean air”) Ozone vs. total nitrogen oxides (NO y ) at eastern U.S. sites [Trainer et al., 1993]

8. Historical records imply a large anthropogenic contribution to the present-day ozone background Ozone trend at European mountain sites, 1870-1990 [Marenco et al., 1994]

9. 8-h daily maximum ozone probability distribution at rural U.S. sites [Lin et al., 2000] AIRS data statistics suggest that background ozone in U.S.has increased by ~3 ppbv over past 20 years 1980-19841994-1998 1980-1984 1994-1998

10. The present ozone background is a sizable increment towards violation of air quality standards 0 20 40 60 80 100 120 ppbv AOT40 (seasonal) NAAQS (8-h avg.) NAAQS (1-h avg.) preindustrialpresent background

11. Growth of Asian emissions over next decades will increase role of background for ozone air quality in U.S. 10 9 atoms N cm -2 s -1 Anthropogenic NOx emissions [IPCC, 2001] 2000 2020 “Optimistic” IPCC scenario: OECD, U.S. down 20% Asia up 50%

12. Modeled increase in U.S. surface ozone (ppbv) from tripling of Asian emissions (1985 to 2015) with other emissions held constant [Jacob et al., 1999]

13. Rising Asian emissions could offset the benefit of domestic emission controls Modeled surface ozone change (ppbv) in July for 25% reduction of U.S. NO x and hydrocarbon emissions with constant Asian emissions (1985) with tripled Asian emissions Jacob et al. [1999]

14. Increase in surface ozone from transatlantic transport of N. American and European pollution [Li et al., 2001] N.American influence on Europe European influence on N. America GEOS-CHEM model results, July 1997

15. GEOS-CHEM: latest generation of global 3-D models of atmospheric chemistry at Harvard 1 o x1 o - 4 o x5 o horizontal resolution, 20-48 layers in vertical Assimilated meteorological data from NASA/GEOS, 1988-2001 Recent/current applications: –Tropospheric ozone : global budget, Asian outflow, U.S., Middle East, N Atlantic, tropics, interannual variability, trends –Stratospheric ozone: coupling with troposphere –Carbon monoxide: global and regional budgets, interannual variability –Organics: hydrocarbons, acetone, HCN, CH 3 I –Aerosols: radionuclides, sulfate, soot, dust, organics (collaborations with NASA/GSFC, Duke, U. Washington) –Satellite retrievals: formaldehyde, NO 2, CO, ozone –Chemical forecasts: TRACE-P, NOAA 2002

16. APPLICATION OF GEOS-CHEM TO THE ORIGIN OF BACKGROUND OZONE IN U.S. IN SUMMER 1995 [Fiore et al., 2001] NASA/GEOS assimilated meteorological data for 1995 2 o x2.5 o horizontal resolution, 26 vertical layers 120 chemical species (O 3 -NO x -hydrocarbon chemistry); aerosol effects on chemistry, radiation SAMI July 1995 inventory for eastern U.S. Evaluation with AIRS, SOS, NARSTO-NE observations

17. SUMMER 1995 AFTERNOON OZONE IN SURFACE AIR OVER THE U.S. AIRS observations GEOS-CHEM (r 2 = 0.4, bias=3 ppbv)

18. FREQUENCY DISTRIBUTION OF SURFACE p.m. O 3 IN WESTERN MASSACHUSETTS IN SUMMER 1995 Observations (squares, triangles) Model (crosses) Air quality standard

19. MEAN AFTERNOON OZONE BACKGROUND IN MODEL, SUMMER 1995 Background is tagged as ozone produced outside the N. American boundary layer (surface-700 hPa)

20. OZONE BACKGROUND IS DEPLETED DURING REGIONAL POLLUTION EPISODES (due to stagnation, short O 3 lifetime) Background (clean conditions) O 3 vs. (NO y -NO x ) At Harvard Forest, Massachusetts Background (pollution episodes)

21. FREQUENCY DISTRIBUTION OF AFTERNOON BACKGROUND OZONE CONCENTRATIONS IN U.S. SURFACE AIR IN SUMMER 1995 (model) summer ensemble vs. pollution episodes Convection upwind occasionally results in high background during pollution episodes

22. Convection upwind can result in high background contributions to ozone pollution episodes Time, days 0 1 2 3 Subsidence inversion Boundary layer Free troposphere Ozone downdraft fast ozone production > 50 ppbv day -1 Convective cloud Ozone pollution episode

23. ASIAN/EUROPEAN POLLUTION ENHANCEMENT OF BACKGROUND OZONE IN U.S. Mean model values, summer 1995 (4 o x5 o resolution) “Natural” background (no anthropogenic emissions of NO x or NMHCs anywhere, but present-day CH 4 ) Asian/European anthropogenic enhancement above natural background (no anthropogenic emissions in North America)

24. RANGE OF ASIAN/EUROPEAN POLLUTION OZONE ENHANCEMENTS OVER THE UNITED STATES ensemble of model results, summer 1995 Max enhancements (up to 14 ppbv) under moderately polluted conditions (50-70 ppbv O3) associated with recent convection MAJOR CONCERN IF OZONE STANDARD WERE TO DECREASE TO 40 or 60 PPBV

25. CONCLUSIONS Surface ozone in U.S. in summer includes a 20-40 ppbv background originating from outside North America Present-day Asian emissions enhance this background by 3-7 ppbv (up to 14 ppbv) Asian influence on surface ozone in U.S. is highest under moderately polluted conditions (50-70 ppbv), less during acute pollution episodes (> 80 ppbv) or clean conditions (< 40 ppbv) Importance of background will increase in the future due to rise in Asian emissions, lower metrics for ozone standard.

26. FUTURE WORK EPA/Harvard modeling collaboration –Examine ozone perturbations from intercontinental transport for future scenarios and sensitivity studies –Examine intercontinental transport of aerosols, ozone- aerosols coupling –Couple Models-3 and GEOS-CHEM to extend the nested-model capability of Models-3 to the global scale. Analysis of aircraft data directed at intercontinental transport: –TRACE-P, spring 2001 (Asian outflow) –NOAA/ITCT, spring 2002 (North American inflow) –INTEX/NA, summer 2004 (North American outflow/inflow) Assimilation of satellite observations into global models –Use global mapping capabilities from satellites to test model simulations of intercontinental transport for CO, ozone, aerosols