MODELING TRANSPORT OF OZONE AND FINE PARTICLES TO AND FROM NORTH AMERICA Daniel J. Jacob Harvard University with Arlene M. Fiore, Rokjin Park, Colette L. Heald and support from EPA (ICAP), EPRI, NOAA

TWO MODES OF INTERCONTINENTAL INFLUENCE 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

MECHANISM FOR TRANSPACIFIC TRANSPORT OF ANTHROPOGENIC OZONE AND FINE PARTICLES entrainment, dilution ASIA PACIFIC NORTH AMERICA NO x, SO 2, VOC warm conveyor belts, convection aerosols, HNO 3 PAN (~10%) VOCs (long-lived) SO x (~10%) OC aerosol PAN O3O3 NO x O3O3 sulfate Boundary layer Free troposphere 2 km subsidence ozone, sulfate, OC HEMISPHERIC POLLUTION

USING GLOBAL CHEMICAL TRANSPORT MODELS TO QUANTIFY INTERCONTINENTAL INFLUENCE (1)Standard simulation; compare w/ observations (2) Set N. American anthropogenic emissions to zero  estimate background (3) Set global anthropogenic emissions to zero  estimate natural background Difference between (1) and (2)  regional pollution Difference between (2) and (3)  intercontinental pollution GEOS-Chem model : driven by NASA/GEOS assimilated meteorological data horizontal resolution 2 o x2.5 o, 48 vertical levels coupled ozone-PM simulation used by 20 research groups in Europe and N. America (~100 publications) extensive evaluation with U.S. observations for ozone [Fiore et al., 2002, 2003ab] and PM [Park et al., 2003, 2004]

Surface ozone at Voyageurs National Park, Minnesota (May-June 2001) CASTNet observations Model Background Natural Stratospheric + * Intercontinental pollution Regional pollution }  } Background: ppbv Natural : 9-23 ppbv Stratosphere: < 7 ppbv X Fiore et al. [2003]

Surface ozone at Yellowstone National Park, Wyoming, 2.5 km altitude (March-May 2001) CASTNet observations Model Background Natural O 3 level Stratospheric + * Intercontinental pollution Regional pollution }  } X Background: ppbv Natural : ppbv Fiore et al. [2003]

Probability distribution of afternoon (1-5 p.m. mean) surface ozone at U.S. CASTNet sites in March-October 2001 Probability. ppbv -1 CASTNet observations GEOS-Chem at CASTNet Natural 18±5 ppbv GEOS-Chem background 26±7 ppbv GEOS-Chem background 29±9 ppbv MOZART-2 Intercontinental pollution enhances background by 8 ± 4 ppbv relative to natural Fiore et al. [2003] Ozone, ppbv

Regional Pollution Ozone (ppbv) Cumulative Probability Low-elevation CASTNet sites, Jun-Aug CASTNet observations GEOS-Chem model Model background * DEPLETION OF OZONE BACKGROUND DURING REGIONAL POLLUTION EPISODES Background (and intercontinental pollution influence) are highest when ozone concentrations are in mid-range (40-70 ppbv), reflecting subsidence conditions Fiore et al. [2003]

GLOBAL OZONE BACKGROUND: METHANE AND NO x ARE THE LIMITING PRECURSORS GEOS-Chem [Fiore et al., 2002a] 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

INCREASE IN FREE TROPOSPHERIC BACKGROUND OZONE OVER EUROPE IN THE PAST CENTURY Observations at mountain sites [Marenco et al., 1994] Preindustrial model ranges Simulated historical ozone levels are higher than observed: is this due to model overestimates in natural sources (lightning) or calibration errors?

OBSERVED TREND IN OZONE BACKGROUND OVER CALIFORNIA IN SPRING SUGGESTS ppbv INCREASE OVER PAST 20 YEARS Trend: ppbv yr -1 Jaffe et al. [2003] …but this is inconsistent with models; e.g., GEOS-Chem model indicates only a 2 ppbv increase over (Fiore et al., 2002b)

AN EXAMPLE OF TRANSPACIFIC TRANSPORT OF ASIAN AEROSOL POLLUTION AS SEEN BY MODIS Detectable sulfate pollution signal correlated with MOPITT CO X10 18 [molecules cm -2 ]

P3B DATA over NW Pacific (30 – 45 o N, 120 – 140 o E) WET SCAVENGING OF ASIAN AEROSOLS DURING LIFTING TO THE FREE TROPOSPHERE Park et al. [2005] TRACE-P observations over NW Pacific (Feb-Mar 2001) and GEOS-Chem simulations Sulfate is most important exported anthropogenic aerosol in model

…BUT ELEVATED OC AEROSOL IS OBSERVED IN FREE TROPOSPHERIC ASIAN OUTFLOW – CONTRIBUTION TO INTERCONTINENTAL POLLUTION? ACE-Asia aircraft observations over Japan (spring 2001) Observed (Huebert) GEOS-Chem correlated with CO – but also a 1-3  g sm -3 background; implies large secondary production of OC in free troposphere missing from present models; OC dominates aerosol loading in free troposphere Observed (Russell) OC/sulfate ratio Colette.L. Heald, Harvard

INTERCONTINENTAL TRANSPORT OF ASIAN AND NORTH AMERICAN ANTHROPOGENIC SULFATE Annual mean values as determined from GEOS-Chem 2001 sensitivity simulations with these sources shut off Intercontinental enhancements of anthropogenic sulfate over U.S. are of same order as interstate enhancement threshold used for regulation (0.2  g m -3 ) and EPA estimates of natural values (  g m -3 ) for Regional Haze Rule Park et al. [2004]

VERTICAL STRUCTURE OF TRANSPACIFIC TRANSPORT GEOS-Chem model results for spring 2001 (15-45 o N) C.L. Heald, Harvard Asian CO Asian sulfate Asia N. America Asia N. America Asian aerosols are transported in lower free troposphere and subside over the NE Pacific; topography in western U.S. promotes contact with surface

EVIDENCE OF ASIAN SULFATE IN IMPROVE NETWORK OF AEROSOL MEASUREMENTS AT U.S. SITES NW US: 0.72 μgm -3 NW US: 1.04 μgm -3 NW US: 0.60 μgm -3 spring 2001 mean 24-h seasonal max GEOS-Chem Asian influence NW US: 0.18 μgm -3 IMPROVE GEOS-CHEM Asian anthr (GEOS-Chem) March 1 April 1 May 1 June 1 Time series over NW U.S. (spring 01) IMPROVE data: spring 2001 mean days of GEOS-Chem 24-h seasonal max 1.4  g m -3 C.L. Heald, Harvard

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) PROBING TRANSPACIFIC POLLUTION TRANSPORT NOAA/ITCT-2K2 aircraft campaign, April-May 2002

EFFECT OF NORTH AMERICAN SOURCES ON EXCEEDANCES OF EU STANDARD (55 ppbv, 8-h av.) 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 anthropogenic emissions Li et al. [2002]

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 out of Hong Kong and Japan, spring 2001

CALIFORNIA MOUNTAIN SITES ARE MOST 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 exceedances of standard; unlike at surface sites, Asian pollution influence is not minimum under high-ozone conditions! Hudman et al. [2004] Observed ozone (ppbv) 8-h running mean Simulated Asian ozone enhancement (ppbv) 8-h running mean