Organic Carbon Aerosol: Insight from recent aircraft field campaigns Colette L. Heald NOAA Climate and Global Change Postdoctoral Fellow (heald@atmos.berkeley.edu) Department of Civil and Environmental Engineering, Stanford University October 27, 2006

AEROSOL IMPACTS ON AIR QUALITY AIR QUALITY / HEALTH VISIBILITY Particulates contribute to urban smog: Clear Day LA April 16, 2001 Visibility reduction at Glen Canyon, Arizona due to transpacific transport of Asian dust [Environmental Working Group Report, 2005]

AEROSOL IMPACTS ON CLIMATE DIRECT EFFECT INDIRECT EFFECT Scattering Radiation = COOLING Absorbing Radiation = WARMING Reflection Refraction Increase cloud albedo = COOLING Increase cloud lifetime = COOLING Absorption

ESTIMATED RADIATIVE FORCING OF CLIMATE [IPCC, 2001] Biogenic OC currently not included in forcing estimates  is it important?

ORGANIC CARBON AEROSOL *Numbers from IPCC [2001] Secondary Organic Aerosol (SOA): 8-40 TgC/yr Reactive Organic Gases Nucleation or Condensation OC Oxidation by OH, O3, NO3 Monoterpenes Fossil Fuel: 10-30 TgC/yr Biomass Burning: 45-80 TgC/yr Aromatics Isoprene Direct Emission Fossil Fuel Biomass Burning BIOGENIC SOURCES ANTHROPOGENIC SOURCES

OBSERVING TROPOSPHERIC COMPOSITION ON ALL SCALES SURFACE SITES AIRCRAFT CAMPAIGNS SATELLITES Chemical characterization throughout the troposphere Continuous, global measurements Long-term monitoring at the surface AIR QUALITY CLIMATE

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

Single particles over NA FIRST SUGGESTIONS OF HIGH ORGANIC CARBON AEROSOL CONCENTRATIONS IN THE FREE TROPOSPHERE High organic loading in the UT High organic loading in the FT Single particles over NA [Murphy et al., Science, 1998] TARFOX (E US) [Novakov et al., JGR, 1998]

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

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

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. Pollution: There is a free tropospheric background of 1-4 μg sm-3 that is not correlated with CO or sulfate. No indication of a primary source for OC in FT

SECONDARY ORGANIC AEROSOL SOA parameterization [Chung and Seinfeld, 2002] VOCi + OXIDANTj  ai,jP1i,j + ai,jP2i,j Parameters (a’s K’s) from smog chamber studies Ai,j Gi,j Pi,j Equilibrium (Komi,j)  also f(POA) Condensation of low vapour pressure ROGs on pre- existing aerosol Reactive Organic Gases Oxidation by OH, O3, NO3 Simulated April Biogenic SOA Biogenic VOCs (eg. monoterpenes) FT observations ~ 4mg/m3 Simulated SOA far too small!

IMPLICATIONS FOR TRANSPACIFIC TRANSPORT High concentrations of OC aerosols measured in the FT over Asia (not captured by models) [Heald et al., 2005] Observed Simulated Asian air masses Sulfate: 0.24 µgm-3 OC: 0.53 µgm-3 Twice as much OC aerosol as sulfate observed at Crater Lake [Jaffe et al., 2005] ASIA NORTH AMERICA PACIFIC

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

ICARTT: COORDINATED ATMOSPHERIC CHEMISTRY CAMPAIGN OVER EASTERN NORTH AMERICA AND NORTH ATLANTIC IN SUMMER 2004 Multi-agency, International Collaboration 2004 fire season in North America: worst fire season on record in Alaska MOPITT Observations of CO Transport (July 17-19) [Turquety et al., submitted] Emissions derived from MODIS hot spots [Turquety et al., submitted] OC: 1.4 TgC OC emissions from biomass burning were 4 times climatological average!

WHAT CONTRIBUTES TO OC AEROSOL OVER NORTH AMERICA? Observed boreal fire Influence down-wind Simulated source attribution for “background” OC NOAA WP-3 Flight tracks BB filtered using CH3CN *includes isoprene as a source of SOA [Kroll et al., 2005] OC concentrations in the free troposphere doubled as a result of Alaskan boreal fires. Is model attribution of remaining OC sources correct?

DO WE UNDERSTAND OC AEROSOL OVER NORTH AMERICA? Sulfur Oxides (SOx) Water soluble OC Aerosol (WSOC) Observed Simulated OC aerosol concentrations 3x lower than observed off of Asia OC aerosol concentrations captured by the model, BUT we cannot simulate variability in observations (R=0.21)  incomplete understanding of formation. [Heald et al., accepted] Note: biomass burning plumes were removed

WHAT DON’T WE UNDERSTAND ABOUT SOA FORMATION? Cloud Processing 1. Production more efficient at low NOx 2. Multi-step oxidation SOA: ?? TgC/yr New formation pathways Nucleation or Condensation OC ROG Heterogeneous Reactions Additional Precursors Oxidation by OH, O3, NO3 FF: 45-80 TgC/yr BB: 10-30 TgC/yr Isoprene Monoterpenes Aromatics Direct Emission Fossil Fuel Biomass Burning BIOGENIC SOURCES ANTHROPOGENIC SOURCES

CONSTRAINTS FROM SATELLITES? AEROSOL OPTICAL DEPTHS 2001/2005 MODIS MISR CAM Community Atmospheric Model (NCAR ESM with MOZART chemistry) Simulated AOD overestimated over land and underestimated over oceans. Retrieval uncertainties larger than SOA signal. MODIS/ MISR Aerosols Land (difficult to characterize reflectance)

CARBON CYCLE AND POTENTIAL RADIATIVE IMPLICATIONS 4 μg/m3 (ACE-Asia) AOD @ 50% RH: 0.057 TOA Radiative Forcing = -1.2 W/m2 OC AEROSOL 1 µg/m3 in the FT globally ~ 100 TgC/yr VOC EMISSIONS 500-1000 TgC/yr [IPCC, 2001] DISSOLVED ORGANIC CARBON IN RAINWATER 430 TgC/yr [Wiley et al., 2000]

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

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