1. INTERCONTINENTAL TRANSPORT OF POLLUTION: POLICY IMPLICATIONS Daniel J. Jacob NO x emissions (2000) with Rynda Hudman, Colette Heald, Duncan Fairlie, Rokjin Park, Solene Turquety, Arlene Fiore (now at GFDL), Qinbin Li (now at JPL) and support from EPRI, EPA, NOAA, NASA

2. OZONE AND PARTICULATE MATTER (PM): TOP TWO AIR POLLUTANTS IN THE U.S. # millions of people living in areas exceeding national ambient air quality standards (NAAQS) [EPA, 2002] 124 ppbv (1-hour) 84 ppbv (8-hour) Carbon monoxide (CO) Lead Nitrogen dioxide Ozone (O 3 ) Particles < 10  m (PM 10 ) Particles < 2.5  m (PM 2.5 ) Sulfur dioxide (SO 2 ) Any pollutant 50  g m -3 (annual) 0 50 100 150 15  g m -3 (annual) millions

3. MECHANISMS FOR INTERCONTINENTAL TRANSPORT BETWEEN NORTHERN MIDLATITUDE CONTINENTS AsiaN. America Europe Boundary layer Free troposphere liftingsubsidence boundary layer advection Tropopause HEMISPHERIC POLLUTION BACKGROUND “Direct” intercontinental transport Mixing Direct intercontinental transport: fast (~1 week) transport from source to receptor continent; either by boundary layer advection or by lifting to lower free troposphere followed by subsidence Hemispheric pollution: pollution mixes in free troposphere, affecting free tropospheric background, in turn affecting surface concentrations by subsidence 2 km

4. ENVIRONMENTAL IMPACTS OF ATMOSPHERIC OZONE NO x = NO + NO 2 : nitrogen oxide radicals VOC (volatile organic compounds) = light hydrocarbons and substituted organic compounds UV shield Greenhouse gas Primary source of OH radicals Smog

5. GLOBAL BUDGET OF TROPOSPHERIC OZONE O3O3 O2O2 h O3O3 OHHO 2 h, H 2 O Deposition NO H2O2H2O2 CO, VOC NO 2 h STRATOSPHERE TROPOSPHERE 8-18 km Chem prod in troposphere 4300 1600 Chem loss in troposphere 4000 1700 Transport from stratosphere 400 Deposition 700 300 Tg O 3 yr -1 present natural NO x, CO, methane, nonmethane VOC (NMVOC) emissions Ozone lifetime: ~ days in boundary layer ~1 mo in free troposphere Inventory (Tg): 360 230 Limiting ozone precursors: Global - NO x and methane Regional – NO x and NMVOCs Mickley et al. [1999] O3O3

6. TROPOSPHERIC OZONE BACKGROUND stratosphere Latitude over NW Pacific Longitude China coast California coast Airborne lidar observations from TRACE-P aircraft mission over N. Pacific in spring 2001 [Browell et al., 2003] 20-70 ppbv ozone background, increases with altitude and latitude

7. OZONE BACKGROUND IS AN IMPORTANT INCREMENT TOWARD EXCEEDANCE OF AIR QUALITY STANDARDS (AQS) 0 20 40 60 80 100 120 ppbv Europe AQS seasonal 8-h avg U.S. AQS 8-h avg. U.S. AQS 1-h avg. Surface background at northern midlatitudes Japan AQS 8-h avg. preindustrial present

8. 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 (lightning, stratosphere)…or calibration errors in the data

9. GEOS-CHEM GLOBAL 3-D MODEL OF ATMOSPHERIC TRANSPORT AND CHEMISTRY Developed by Harvard Atmospheric Chemistry Modeling Group, used by 17 research groups in N. America and Europe; ~100 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, aerosols (PM), CO 2, methane, mercury, hydrogen,… nested with EPA CMAQ regional model for studies of intercontinental transport Results presented today are from coupled ozone-aerosol simulation with 2 o x2.5 o resolution, 48 vertical levels

10. MEAN SURFACE OZONE ENHANCEMENTS FROM ANTHROPOGENIC NO x AND NMVOC EMISSIONS IN 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.

11. Fiore et al. [2002]; Li et al. [2002] tropical air Subsidence of Asian pollution + local production stagnation RANGE OF INTERCONTINENTAL OZONE POLLUTION ENHANCEMENTS AT SURFACE SITES (GEOS-CHEM model) over U.S. over Europe effect is maximum for ozone concentrations in mid-range (40-70 ppbv)

12. EFFECT OF NORTH AMERICAN SOURCES ON EXCEEDANCES OF EUROPEAN AIR QUALITY STANDARD (55 ppbv, 8-h average) GEOS-CHEM model results, summer 1997 Number of exceedance days (out of 92) # of exceedance days that would not have been in absence of N.American emissions Li et al. [2002]

13. NOAA/ITCT-2K2 AIRCRAFT CAMPAIGN IN APRIL-MAY 2002 Monterey, CA High-ozone Asian pollution plumes observed in lower free troposphere but not at surface (Trinidad Head); strong stratospheric influence (Trinidad Head sondes) CO O3O3 PAN HNO 3 May 5 plume at 6 km: High CO and PAN, no O 3 enhancement May 17 subsiding plume at 2.5 km: High CO and O 3, PAN  NO x  HNO 3 Hudman et al. [2004] Observations by D. Parrish, J. Roberts, T. Ryesrson (NOAA/AL)

14. CONCEPTUAL PICTURE OF OZONE PRODUCTION IN TRANSPACIFIC ASIAN POLLUTION PLUMES NO x HNO 3 PAN Asian boundary layer (OPE ~ 5) PAN, weak  O 3 Warm conveyor belt; 5-10% export of NO y mainly as PAN strong  O 3 Subsidence Over E Pacific OPE 60-80 PAN  NO x  HNO 3 U.S. boundary layer very weak  O 3 10x dilution (Asian dust data) E. Asia Pacific United States Hudman et al. [2004] Stratospheric downwelling GEOS-CHEM ozone production efficiency (2-4 km)

15. SURFACE OZONE AT TRINIDAD HEAD, CALIFORNIA DURING ITCT-2K2 May 17 Neither observations nor models show much variability; Asian pollution enhancement (6 ± 2 ppbv in GEOS-CHEM) is significant but undetectable Goldstein et al. [2004]

16. 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]

17. 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 another 4- 6 ppbv enhancement in surface ozone over U.S.

18. OBSERVATIONS OF INTERCONTINENTAL TRANSPORT DURING ICARTT AIRCRAFT CAMPAIGN (Jul-Aug 2004) AIRS satellite observationsGEOS-CHEM near real time simulation Asian pollution U.S. pollution Alaskan fires Wallace McMillan (UMBC)Solene Turquety (Harvard) Carbon monoxide (CO) columns on July 18

19. ASIAN POLLUTION PLUME OFF CALIFORNIA sampled by NASA aircraft on July 1, 2004 GEOS forecast Asian CO (9 km)AIRS satellite CO data Asian pollution S. Pawson (NASA), W. McMillan (UMBC), M/ Avery (NASA), S.Turquety (Harvard). L. Jaegle (UW)

20. ASIAN POLLUTION PLUME OVER EASTERN U.S. sampled by NASA aircraft on July 15 Observed  O 3 = 20-40 ppbv,  CO = 20 ppbv GEOS-CHEM  O 3 = 5-10 ppbv,  CO = 10-20 ppbv High Halon-1211 in plume confirms Asian origin GEOS forecast Asian CO (9 km) Observed O 3 (ppbv) Observed CO (ppbv)

21. POLICY-RELEVANT OZONE BACKGROUND (PRB) USED FOR SETTING OF U.S. 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…and used to argue that NAAQS is unattainable Can natural background indeed be so high as to make current standard unattainable?

22. 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

23. 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 and is in fact too high Ozone (ppbv) Cumulative Probability Regional Pollution Daily mean afternoon O 3 at 58 U.S. CASTNet sites June-July-August Fiore et al. [2003]

24. ATMOSPHERIC PARTICULATE MATTER (AEROSOLS) Soil dust Sea salt Aerosol: dispersed condensed matter suspended in a gas Size range: 0.001  m (molecular cluster) to 100  m (small raindrop) SO 2, NO x, NH 3, VOCs Most important components of the atmospheric aerosol: -Sulfate- nitrate-ammonium -Organic carbon (OC), elemental carbon (EC) -Soil dust -Sea salt

25. AIRCRAFT OBSERVATIONS IN ASIAN WARM CONVEYOR BELT (WCB) OUTFLOW ILLUSTRATE SCAVENGING OF AEROSOLS DURING LIFTING TO FREE TROPOSPHERE Longitude Data from E.V. Browell boundary layer outflow WCB outflow Ozone: WCB outflow Aerosols scavenged from WCB outflow TRACE-P campaign, spring 2001

26. GEOS-CHEM SIMULATION OF TRACE-P OBSERVATIONS BC underestimated by factor of 2 because emissions [Bond et al.] are too low Park et al. [2004b] P3B DATA over NW Pacific (30 – 45 o N, 120 – 140 o E) Scavenging from Asian outflow is 80-90% efficient for sulfate and BC, ~100% for nitrate Black carbon (BC)

27. DUST STORMS PROVIDE VISIBLE EVIDENCE OF INTERCONTINENTAL TRANSPORT OF AEROSOLS 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

28. ASIAN AEROSOL POLLUTION INFLUENCE OVER WESTERN U.S. - * - AERONET __GEOS-CHEM __ Asian SO 4 2- +NH 4 + +NO 3 - __ Asian dust Spring 2001 AERONET aerosol optical depth (AOD) measurements at Missoula, MT Colette Heald et al. (Harvard) AOD

29. MEAN ASIAN POLLUTION INFLUENCES ON SURFACE AEROSOL CONCENTRATIONS Annual means determined from a GEOS-CHEM 2001 sensitivity simulation with Asian anthropogenic sources shut off Park et al. [2004a] SO 4 2- NO 3 - NH 4 +  g m -3 Enhancements are low relative to air quality standard (15  g m -3 )

30. EPA REGIONAL HAZE RULE Requires linear improvement in visibility over 2004-2018 at federal class I areas (large national parks) toward a 2064 natural visibility endpoint Visibility is a logarithmic function of aerosol extinction  ~50% reduction in anthropogenic emissions required by 2018, sensitive to the definition of the 2064 endpoint deciviews: dv = 10ln(b ext /10), where b ext is aerosol extinction from EPA [2001]

31. VISIBILITY DEGRADATION STATISTICS IN THE UNITED STATES (2001): MODEL vs. OBSERVATIONS Visibility decrease (deciviews: dv = 10ln(b ext /10) ) from sulfate, nitrate, and carbonaceous aerosols R.J. Park (Harvard) Observations (IMPROVE network)GEOS-CHEM

32. EPA “NATURAL DEFAULT CONCENTRATIONS” FOR THE REGIONAL HAZE RULE ARE TOO LOW  g m -3 Western U.S. …and don’t allow for large enhancement from transboundary pollution Park et al. [2004a]

33. IMPLICATIONS FOR EMISSION REDUCTIONS 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]

34. WHERE ARE ASIAN EMISSIONS HEADED? It’s anyone’s guess Past trends and future projections of Chinese SO 2 emissions [Streets et al., 2002]