1. Organic Carbon Aerosol Colette L. Heald University of California, Berkeley NOAA Summer Institute, Steamboat Springs, CO July 12, 2006

2. CURRENT UNDERSTANDING: SOURCES OF ORGANIC CARBON AEROSOL Reactive Organic Gases Oxidation by OH, O 3, NO 3 Direct Emission Fossil Fuel Biomass Burning Monoterpenes Nucleation or Condensation Aromatics ANTHROPOGENIC SOURCESBIOGENIC SOURCES OC FF: 45-80 TgC/yr BB: 10-30 TgC/yr Secondary Organic Aerosol (SOA): 8-40 TgC/yr *Numbers from IPCC [2001]

3. Formation and Transport Emissions: 1.Anthropogenic 2.Natural/Biogenic ORGANIC AEROSOLS: AIR QUALITY, CHEMISTRY AND CLIMATE Air Quality Impacts: 1.Visibility 2.Health Climate Forcing 1. Direct: Scatter solar radiation 2. Indirect: ↑ cloud albedo ↑ cloud lifetime

4. ORGANIC CARBON AEROSOL: AT THE SURFACE Organic carbon constitutes 10-70% of aerosol mass at surface. Difficult to distinguish primary from secondary contributions. 2004 NARSTO Assessment

5. ACE-ASIA: FIRST OC AEROSOL MEASUREMENTS IN THE FREE TROPOSPHERE Mean Observations Mean Simulation Observations + Concentrations of OC in the FT were under-predicted by a factor of 10-100! (ACE-Asia aircraft campaign conducted off of Japan during April/May 2001) GEOS-Chem: Global Chemical Transport model [Heald et al., 2005] [Mader et al., 2002] [Huebert et al., 2003] [Maria et al., 2003]

6. CONTRAST: OTHER AEROSOLS IN ASIAN OUTFLOW Model simulates both the magnitude and profile of sulfate and elemental carbon (EC) during ACE-Asia Mean Observations Mean Simulation (GEOS-Chem) Scavenging Secondary production

7. ANY INDICATION THAT DIRECT EMISSIONS ARE UNDERESTIMATED? Biomass Burning: Satellite firecounts show no active fires in Siberia Agricultural fires in SE Asia do not contribute in the FT. No apparent underestimate in primary emissions Pollution: There is a free tropospheric background of 1-4 μg sm -3 that is not correlated with CO or sulfate.

8. SECONDARY ORGANIC AEROSOL Biogenic VOCs (eg. monoterpenes) Reactive Organic Gases Oxidation by OH, O 3, NO 3 Secondary Organic Aerosol Condensation of low vapour pressure ROGs on pre- existing aerosol Simulated April Biogenic SOA FT observations ~ 4  g/m 3 Simulated SOA far too small! SOA parameterization [Chung and Seinfeld, 2002] VOC i + OXIDANT j   i,j P1 i,j +  i,j P2 i,j Parameters (  ’s K’s) from smog chamber studies A i,j G i,j P i,j Equilibrium (Kom i,j )  also f(POA)

9. SEVERAL STUDIES SUGGESTING UNDERESTIMATE OF SOA [Volkamer et al., 2006] Global underestimate in SOA?

10. OC AEROSOL OVER NORTH AMERICA: ICARTT CAMPAIGN NOAA WP-3 Flight tracks Note: biomass burning plumes were removed OC aerosol concentrations captured by the model, BUT we cannot simulate variability in observations (R=0.21)  incomplete understanding of formation. Observed Simulated Water soluble OC Aerosol OC aerosol concentrations 3x lower than observed off of Asia [Heald et al., submitted] 2004: worst fire season on record in Alaska Emissions derived from MODIS hot spots [Turquety et al., submitted]

11. WHAT DON’T WE UNDERSTAND ABOUT SOA FORMATION? ROG Oxidation by OH, O 3, NO 3 Direct Emission Monoterpenes Nucleation or Condensation Aromatics OC Isoprene Cloud Processing FF: 45-80 TgC/yr BB: 10-30 TgC/yr SOA: ?? TgC/yr Fossil Fuel Biomass Burning ANTHROPOGENIC SOURCESBIOGENIC SOURCES Heterogeneous Reactions Additional Precursors 1. Production more efficient at low NOx 2. Multi-step oxidation New formation pathways

12. CARBON CYCLE AND POTENTIAL RADIATIVE IMPLICATIONS VOC EMISSIONS 500-1000 TgC/yr [IPCC, 2001] DISSOLVED ORGANIC CARBON IN RAINWATER 430 TgC/yr [Wiley et al., 2000] OC AEROSOL 1 µg/m 3 from 2-7 km globally = 105 TgC/yr 4 μg/m 3 (ACE-Asia) AOD @ 50% RH: 0.057 TOA Radiative Forcing = -1.2 W/m 2

13. CURRENT WORK: HOW WILL SOA FORMATION RESPOND TO A FUTURE CLIMATE? Biogenic Emissions of precursors: T/light/moisture Anthropogenic Emissions: Increasing aromatic emissions More surface area for aerosol condensation Precipitation: Enhanced removal Oxidant levels: Effected by hydrological cycle and anthropogenic pollution levels Using a coupled land-atmosphere model (NCAR CCSM)

14. ACKNOWLEDGEMENTS Daniel Jacob, Rokjin Park, Solène Turquety, Rynda Hudman Barry Huebert Lynn Russell John Seinfeld, Hong Liao Rodney Weber, Amy Sullivan Rick Peltier ITCT-2K4 Science Team Hosts: Inez Fung & Allen Goldstein