1. Transpacific transport of anthropogenic aerosols and implications for North American air quality EGU, Vienna April 27, 2005 Colette Heald, Daniel Jacob, Rokjin Park, Becky Alexander, Duncan Fairlie, Allen Chu (GSFC), Robert Yantosca

2. Clear Day TRANSPACIFIC TRANSPORT OF ASIAN AEROSOLS Most documented cases consist of transport of dust: Despite their short lifetimes, aerosols can be transported across the Pacific and can affect North American air quality standards and visibility. BUT Model simulations suggest that anthropogenic aerosols from Asia can ALSO be transported to the United States [Park et al., 2004] April 16, 2001 Visibility reduction at Glen Canyon, Arizona due to transpacific transport of Asian dust Asian contribution is comparable to “natural” standard set by EPA Haze Rule

3. Direct Emission OC BC Dust TRANSPACIFIC TRANSPORT OF ASIAN AEROSOLS ASIA PACIFICNORTH AMERICA Precursor gases SO x NO x NH 3 VOC s Deposition Aerosol Transport Subsidence We have observations of outflow from Asia (can verify emissions) We can compare simulated aerosols with ground station observations over NA Need to verify that we accurately predict transpacific transport  SATELLITES  EPA Haze Rule

4. GEOS-CHEM GLOBAL CTM OXIDANT-AEROSOL SIMULATION Dust SO 4 2- + NO 3 - + NH 4 + Black CarbonOrganic CarbonSeasalt Aerosol Optical Depth (AOD) over the Pacific (during Spring) is dominated by dust and sulfate Bey et al. [2001], Park et al. [2003], Park et al. [2004], Alexander et al. [2004], Fairlie et al. [2005] AOD (550 nm) http://www-as.harvard.edu/chemistry/trop/geos/index.html

5. MARINE SOURCE OF ORGANIC CARBON AEROSOL 2 POSSIBLE MECHANISMS: 1.Direct Emission with sea salt 2.Secondary Production Ocean Surfactant Layer (with Organics) WIND Sea-spray emission of sea salt (and OC) Ocean Surfactant Layer (with HCs) Emission of HCs HC+oxidant  OC In GEOS-CHEM concentrations of OC are underestimated in the MBL We simulate marine OC as co-emitted with sea salt. Lifetime is short. Annual Mean OC (Surface)

6. TRANSPACIFIC TRANSPORT DURING THE SPRING GEOS-CHEM underestimates MODIS observations by factor of ~2 in Spring (both in the background and in outflow) X10 18 [molecules cm -2 ] NO MOPITT DATA AVAILABLE

7. WHAT CAN AERONET TELL US? Is the model/MODIS bias primarily a model underestimate or a satellite retrieval bias? AERONET sites indicate a possible MODIS retrieval bias (not correlated with cloud cover). AERONET MODIS Global AERONET sites (Spring means) MODIS AERONET GEOS-CHEM

8. ALTITUDE OF TRANSPORT (15-45ºN) Asian anthropogenic aerosols are primarily transported in the lower FT Elevated topography over W US enhances surface contribution from Asia

9. 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 ]

10. LINKING TRANSPACIFIC TRANSPORT EVENTS Mean AOD over W. Pacific (160-130W) Asian events contribute to NA surface enhancements 1 23 4 5 6 23 5 6 IMPROVE GEOS-CHEM Asian anthr (GEOS-CHEM)

11. IMPACT OF ASIAN SULFATE ON U.S. AIR QUALITY Asian aerosols preferentially impact ground sites in the NW US. Observations at IMPROVE sites are elevated from mean when simulated Asian influence is high NW US: 0.18 μgm -3 NW US: 0.60 μgm -3 NW US: 0.72 μgm -3 NW US: 1.04 μgm -3

12. PROJECTED SO x EMISSIONS IN ASIA Increasing SO x emissions from Asia will degrade North American air quality and present a further barrier to attainment of domestic air quality regulations in the United States (eg. EPA Haze Rule) courtesy: David Streets One projection suggests that emissions of SO x will more than double in China between 1995-2020 [Streets & Waldhoff, 2000]