1. INTERCONTINENTAL PM AND OZONE POLLUTION: IMPLICATIONS FOR AIR QUALITY STANDARDS Daniel J. Jacob Harvard University http://www-as.harvard.edu/chemistry/trop with support from EPA (ICAP), EPRI, NOAA, NASA NO x emissions (2000)

2. GEOS-CHEM GLOBAL 3-D MODEL OF ATMOSPHERIC TRANSPORT AND CHEMISTRY Model developed by Harvard Atmospheric Chemistry Modeling Group, presently used by 17 research groups in North America and Europe; documented in ~80 research publications. http://www-as.harvard.edu/chemistry/trop/geos driven by GEOS assimilated meteorological observations from NASA Global Modeling and Assimilation Office (GMAO); native resolution 1 o x1 o applied to simulations of ozone, PM, CO 2, methane, mercury, hydrogen,… nested with EPA CMAQ regional model for studies of intercontinental transport (with Daewon Byun, Carey Jang) Results presented today are from coupled ozone-PM simulation with 2 o x2.5 o resolution, 48 vertical levels

3. DUST STORMS PROVIDE VISIBLE EVIDENCE OF INTERCONTINENTAL TRANSPORT Glen Canyon, AZ Clear dayApril 16, 2001: Asian dust! …and anthropogenic pollution is transported together with the dust Colette Heald et al. (Harvard) satellite data

4. ASIAN PM POLLUTION INFLUENCE OVER WESTERN U.S. - * - AERONET __GEOS-CHEM __ Asian SO 4 +NH 4 +Nit __ Asian Dust Spring 2001 What about in surface air? Observations at clean western U.S. sites indicate Asian sulfate influence up to 2.2  g m -3 (24-h average) [Jaffe et al., 2003a] AERONET aerosol optical depth (AOD) measurements at Missoula, MT Colette Heald et al. (Harvard) AOD

5. MEAN ASIAN POLLUTION INFLUENCE ON PM OVER U.S. Annual means as determined from a GEOS-CHEM 2001 sensitivity simulation with Asian anthropogenic sources shut off SO 4 2- NO 3 - NH 4 +  g m -3 Park et al. [2004] Mean sulfate enhancement ~ 0.1  g m -3 ; low relative to NAAQS …though comparable to threshold used in interstate transport rule

6. IMPLICATIONS FOR REGIONAL HAZE RULE  g m -3 Western U.S. We find that EPA natural default for application of the RHR is too low because of: transboundary transport of sulfate pollution (including half from Asia) underestimate of forest fire influences Definition of 2064 “natural visibility” endpoint: should it allow for transboundary pollution? Park et al. [2004]

7. IMPLICATIONS FOR EMISSION REUCTIONS IN PHASE 1 (2004-2018) IMPLEMENTATION OF REGIONAL HAZE RULE Illustrative calculation for mean western U.S. conditions, assuming linear relationship between emissions and PM concentrations, and assuming constant anthropogenic sources from foreign countries between now and 2064 Desired trend in visibility Required % decrease of U.S. anthropogenic emissions Phase 1 30% 48% Park et al. [2004]

8. ENHANCEMENT OF OZONE BACKGROUND DUE TO INTERCONTINENTAL POLLUTION: IMPLICATIONS FOR MEETING AIR QUALITY STANDARDS 0 20 40 60 80 100 120 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.)

9. OZONE BACKGROUND AT NORTHERN MID-LATITUDES HAS A LARGE ANTHROPOGENIC COMPONENT Observations at mountain sites in Europe [Marenco et al., 1994] Preindustrial model ranges Model overestimates of 19 th century observations could reflect model errors in natural ozone sources (esp. lightning NO x )…or calibration errors in the data

10. TREND IN OZONE BACKGROUND OVER WESTERN U.S In contrast, models find background increase of only ~3 ppbv for that period Observations suggest 10-15 ppbv springtime increase over past 20 years according to Jaffe et al. [2003b]…but this is controversial Jaffe et al. [2003b]

11. MEAN SURFACE OZONE ENHANCEMENTS FROM ANTHROPOGENIC NO x AND NMVOC EMISSIONS BY DIFFERENT CONTINENTS GEOS-CHEM model, July 1997 North America Europe Asia Li et al. [2002] as determined from sensitivity simulations with these sources shut off 2-6 ppbv mean enhancements over U.S.

12. Fiore et al. [2002a] tropical air Subsidence of Asian pollution + local production stagnation VARIABILITY OF INTERCONTINENTAL OZONE POLLUTION AT SURFACE SITES Effect is maximum (up to 14 ppbv) for ozone concentrations in mid-range (40-70 ppbv) GEOS-CHEM simulation (summer 1995); enhancements relative to simulation with N. American anthropogenic emissions of NO x and NMVOC shut off

13. INTERCONTINENTAL OZONE POLLUTION LAYERS ARE FREQUENTLY OBSERVED AT HIGH ALTITUDE…BUT NOT AT SURFACE CO O3O3 PAN Aircraft observations from ITCT-2K2 campaign out of Monterey, CA (April-May 2002); enhancements up to 40 ppbv in high-ozone layers Trinidad Head surface observations: Asian pollution enhancement in model is 6 ± 2 ppbv Dilution appears to greatly dampen ozone enhancements at surface: May 17 Hudman et al. [2004]; Goldstein et al. [2004]

14. CALIFORNIA MOUNTAIN SITES ARE PARTICULARLY SENSITIVE TO ASIAN OZONE POLLUTION …because there is less dilution Observed 8-h ozone at Sequoia National Park (1800 m) in May 2002 vs. corresponding simulated (GEOS-CHEM) Asian pollution ozone enhancement Asian enhancements are 6-10 ppbv during NAAQS exceedances; unlike at surface sites, Asian pollution influence is not minimum under high-ozone conditions! May 17 obs. Asian plume event in red Hudman et al. [2004]

15. IMPORTANCE OF METHANE FOR THE TROPOSPHERIC OZONE BACKGROUND Fiore et al., [2002b] Sensitivity of global tropospheric ozone inventory (Tg) in GEOS-CHEM to 50% global reductions in anthropogenic emissions: NO x and methane have the greatest impacts Anthropogenic methane causes 4- 6 ppbv enhancement in surface ozone over U.S.

16. POLICY-RELEVANT OZONE BACKGROUND (PRB) USED FOR SETTING OF NAAQS NAAQS (8-h avg.) 0 20 40 60 80 ppbv Natural background Present –day background at northern midlatitudes PRB is defined as the ozone concentration that would be present in absence of North American anthropogenic emissions PRB used for present NAAQS Risk increment Frequent observations at remote U.S. sites attributed by Lefohn et al. [2001] to natural background Is natural background so high as to make current NAAQS unattainable, as argued by Lefohn et al. [2001]?

17. Ozone time series at CASTNet sites used by Lefohn et al. [2001] At low-elevation sites: background = 20-35 ppbv, natural = 10-25 ppbv Fiore et al. [2003] + * Observations (1-5 pm average) Background (no anthrop. emissions in N. America, present methane) Natural (no anthrop. emissions globally, preindustrial methane) Model: Base (2001) Stratospheric influence Occurrences of high values reflect either regional pollution or a high-altitude site

18. BACKGROUND OZONE IS DEPLETED IN POLLUTION EPISODES CASTNet sites Model Background Natural Stratospheric + * Background on polluted days is 20-25 ppbv, below current PRB of 40 ppbv  Current NAAQS underestimates health risks Ozone (ppbv) Cumulative Probability Regional Pollution Daily mean afternoon O 3 at 58 U.S. CASTNet sites June-July-August Fiore et al. [2003]

19. SATELLITE OBSERVATIONS OF INTERCONTINENTAL TRANSPORT DURING ICARTT AIRCRAFT CAMPAIGN (Jul-Aug 2004) AIRS CO Column July 18 th GEOS-CHEM CO Column July 18 th Asian pollution U.S. pollution Alaskan fires Wallace McMillan (UMBC)Solene Turquety (Harvard) Asian pollution plumes sampled at 5-10 km over eastern U.S. contained over 100 ppbv ozone; Asian origin was confirmed by observations of elevated halon-1211 (manufactured only in China)

20. FUTURE RESEARCH NEEDS Nested global-regional models resolving scales from global to urban (e.g., coupled GEOS-CHEM/CMAQ model presently used at OAQPS) Observing systems directed at intercontinental transport: - satellites (joint EPA/NOAA/NASA workshop, Sept. 04) - aircraft missions (INTEX-B over U.S. west coast in spring 2006, China mission in 2008) - enhancements of surface networks (lidars) Involvement of regulation and policy communities to define critical policy-relevant uncertainties and issues

21. LITERATURE CITED Fiore, A.M., et al., Background ozone over the United States in summer: Origin,trend, and contribution to pollution episodes, J. Geophys. Res., 107, doi:10.1029/2001JD000982, 2002a. Fiore, A.M., et al., Linking ozone pollution and climate change: The case for controlling methane, Geophys. Res. Lett., 29, 1919, 2002b. Fiore, A.M., et al., Variability in surface ozone background over the United States: Implications for air quality policy, J. Geophys. Res., 108, 4787, 2003. Goldstein, A.H., et al., Impact of Asian emissions on observations at Trinidad Head, California, during ITCT 2K2, J. Geophys. Res., in press. Hudman, R. C., et al., Ozone production in transpacific Asian pollution plumes and implications for ozone air quality in California, J. Geophys. Res., in press, 2004. Jaffe D.A., et al., Increasing background ozone during spring on the west coast of North America. Geophys.Res Lett. 30, 1613, 2003a. Jaffe, D., et al.,, Six ’new’ episodes of trans-Pacific transport of air pollutants, Atmos. Environ., 37, 391-404, 2003b. Li, Q.B., et al., Transatlantic transport of pollution and its effects on surface ozone in Europe and North America, J. Geophys. Res., 107, doi:10.1029/2001JD001422, 2002. Park, R. J., et al.,, Natural and transboundary pollution influences on sulfate-nitrate-ammonium aerosols in the United States: implications for policy, J. Geophys. Res., 109, D15204, 10.1029/2003JD004473, 2004.