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Investigating Sources of Organic Carbon and Tracking Transpacific Transport

Explore the impact of Asian aerosols on North American air quality and visibility, integrating observations from MODIS satellites and GEOS-CHEM models. Assess transboundary pollution and projected SOx emissions to understand global atmospheric changes.

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Investigating Sources of Organic Carbon and Tracking Transpacific Transport

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  1. Investigating sources of organic carbon and tracking transpacific transport: Integrating aerosol observations and models Atmospheric Physics Seminar, University of Toronto November 21, 2005 Colette L. Heald

  2. GROWTH IN EAST ASIA IS THE MAJOR DRIVER FOR GLOBAL ATMOSPHERIC CHANGE Asian CO ↑ 60% Will influence hemispheric air quality and radiative forcing

  3. Visibility reduction at Glen Canyon, Arizona due to transpacific transport of Asian dust April 16, 2001 Clear Day TRANSPACIFIC TRANSPORT OF ASIAN AEROSOLS Despite their short lifetimes, aerosols can be transported across the Pacific and can affect North American air quality standards and visibility. Most documented cases consist of transport of dust: BUT Model simulations suggest that anthropogenic aerosols from Asia can ALSO be transported to the United States [Park et al., 2004] Asian contribution is comparable to “natural” standard set by EPA Haze Rule (0.12 µgm-3)

  4. AEROSOL CONCENTRATIONS IN THE U.S.:contributions from natural sources and transboundary pollution Annual regional means from GEOS-CHEM standard and sensitivity simulations Regional Haze Rule objective for 2064 in parks and wilderness areas • EPA default natural concentrations are too low by factors of 2-3 except for OC in eastern U.S. – quantifying fire influences is critical • Transboundary pollution influence from Asia is comparable in magnitude to that from Canada + Mexico [Park et al., 2003, 2004]

  5. TRANSPACIFIC TRANSPORT OF ASIAN AEROSOLS We have observations of outflow from Asia (can verify emissions) Need to verify that we accurately predict transpacific transport  SATELLITES  We can compare simulated aerosols with ground station observations over NA Transport Aerosol Precursor gases SOx NOx NH3 VOCs Direct Emission OC BC Dust Deposition Subsidence EPA Haze Rule ASIA PACIFIC NORTH AMERICA

  6. MODIS OBSERVATIONS • Aboard the Terra and Aqua satellites • Measuring radiance in solar to IR wavelengths (0.43-14 um) • Retrieve total aerosol optical depth at 550 nm • Pixel resolution of 1km, swath width 2330 km  global coverage in 3 days • Different retrieval algorithms over ocean and land MODIS Aerosols Land (difficult to characterize reflectance)

  7. GEOS-CHEM GLOBAL CTM OXIDANT-AEROSOL SIMULATION http://www-as.harvard.edu/chemistry/trop/geos/index.html Bey et al. [2001], Park et al. [2003], Park et al. [2004],Alexander et al. [2004], Fairlie et al. [2005] Dust Sulfate Aerosol Optical Depth (AOD) over the Pacific (during Spring) is dominated by dust and sulfate Black Carbon Organic Carbon Seasalt AOD (550 nm)

  8. DIFFERENTIAL TRANSPORT OF AEROSOLS AND COOBSERVED FROM SPACE Anthropogenic plume, similar for CO and aerosols (allowing for aerosol scavenging) March 2001 Biomass burning plume for CO – Not observed for aerosols

  9. TRANSPACIFIC TRANSPORT (2001) MODIS AOD GEOS-Chem AOD Sulfate AOD Dust AOD peak Asian dust ALSO substantial anthropogenic aerosol transport GEOS-CHEM underestimates MODIS observations by factor of ~2 in Spring

  10. MODIS AERONET GEOS-CHEM WHAT CAN AERONET OBSERVATIONS 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).

  11. AN EXAMPLE OF TRANSPACIFIC TRANSPORT OF ASIAN AEROSOL POLLUTION AS SEEN BY MODIS April 25, 2001 April 26, 2001 April 27, 2001

  12. IMPROVE obs GEOS-Chem GEOS-Chem (Asian) TRANSPACIFIC TRANSPORT EVENTS AT SURFACE SITES Midway Island (central North Pacific) IMPROVE Sites (NW United States) 4 transpacific events tracked at surface sites

  13. IMPACT OF ASIAN SULFATE ON U.S. AIR QUALITY Observed during Asian events NW US: 1.04 μgm-3 Observed NW US: 0.72 μgm-3 Asian events NW US: 0.60 μgm-3 Simulated Asian NW US: 0.18 μgm-3 Asian aerosols preferentially impact ground sites in the NW US. Observations at IMPROVE sites are elevated from mean when simulated Asian influence is high [Heald et al., 2005b]

  14. PROJECTED SOx EMISSIONS IN ASIA • One projection suggests that • emissions of SOx will more than • double in China between • 1995-2020 • [Streets & Waldhoff, 2000] courtesy: David Streets Increasing SOx emissions from Asia could 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)

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

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

  17. What is the source of this FT organic carbon aerosol? Mean Observations Mean Simulation Observations + ACE-ASIA: OC AEROSOL MEASUREMENTS IN THE FREE TROPOSPHERE (ACE-Asia aircraft campaign conducted off of Japan during April/May 2001) Seinfeld group Huebert group Russell group High Levels of OC were observed in the FT during ACE-Asia by 2 independent measurement techniques. We cannot simulate this OC with direct emissions

  18. Mean Observations Mean Simulation (GEOS-Chem) DO WE UNDERSTAND OTHER AEROSOLS? Secondary production Scavenging Scavenging GEOS-Chem simulates both the magnitude and shape of sulfate and EC concentrations throughout the troposphere  what is different about OC?

  19. ANY INDICATION THAT DIRECT EMISSIONS ARE UNDERESTIMATED? • Biomass Burning: • Satellite firecounts show no active fires in Siberia • OC aerosol from agricultural burning in SE Asia emitted earlier in the season, at lower latitudes and is not injected into the FT • Pollution: • Although the highest aerosol observations are associated with elevated CO, there is a free tropospheric background of 1-3 μg sm-3 that is not correlated with CO or sulfate.

  20. IS SECONDARY ORGANIC AEROSOL (SOA) THE EXPLANATION? SOA is a good candidate because can condense more easily with colder temperature (i.e. higher altitude) Secondary Organic Aerosol Condensation of low vapour pressure ROGs on pre-existing aerosol GEOS-CHEM April Biogenic SOA Reactive Organic Gases [Chung and Seinfeld, 2002] mechanism Oxidation by OH, O3, NO3 Biogenic VOCs (eg. monoterpenes) FT observations ~ 4mg/m3 Biogenic SOA far too small!

  21. 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] High concentrations of OC aerosols measured in the FT over Asia (not captured by models) [Heald et al., 2005a] IMPLICATIONS FOR TRANSPACIFIC TRANSPORT ASIA NORTH AMERICA PACIFIC

  22. CARBON CYCLE AND POTENTIAL RADIATIVE IMPLICATIONS 4 ug/sm3 (ACE-Asia) AOD @ 50% RH: 0.057 TOA Radiative Forcing = -1.2 W/m2 OC AEROSOL 1 µg/sm3 from 2-7 km globally = 105 TgC/yr DISSOLVED ORGANIC CARBON IN RAINWATER 430 TgC/yr [Willey et al., 2000] VOC EMISSIONS 500-1000 TgC/yr [IPCC, 2001] [Heald et al., 2005a]

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

  24. UNDERESTIMATE OF OC AEROSOL DURING ICARTT Observations GEOS-Chem Simulation NOAA ITCT-2K4 flight tracks (R. Weber’s PILS instrument aboard) WSOMCx2 WSOMC OMC SOA Same underestimate in OC aerosol observed over North America. Note: biomass burning plumes were removed

  25. INCLUDING ISOPRENE AS A SOURCE OF SOA Recent study: yield of SOA from isoprene is 0.9-3.0%[Kroll et al., 2005]. Isoprene oxidation products have been observed in the particulate phase [Matsunaga et al., 2005] GEIA Emissions July/August 2004 10% yield = 0.8 Tg SOA 3% yield = 0.4 Tg SOA Applying smog chamber estimates [Kroll et al., 2005] to isoprene emissions inventories suggests a 50% increase in the SOA source over NA.

  26. IS SCAVENGING OF OC AEROSOLS OVERESTIMATED IN MODELS? Hydrophillic aerosols are wet scavenged assuming 100% solubility. Recent analysis of cloud events at Puy de Dome suggest scavenging efficiency of OC is much lower [Sellegri et al., 2003] Observations GEOS-Chem Simulation GEOS-Chem Simulation (with scavenging e=0.14) A large decrease in scavenging efficiency increases OMC concentrations throughout the troposphere, however discrepancies remain in the BL

  27. ORGANIC CARBON IN THE FT: AN ONGOING QUESTION • Chemistry leading to SOA production is not well understood! • Global Models currently do not include: • SOA formation in clouds [Lim et al., 2005] • SOA from isoprene [Claeys et al., 2004; Kroll et al., 2005; Matsunaga et al., 2005] • Uptake of carbonyls on aerosols [Liggio et al., 2005] • Multi-stage oxidation of long-lived oxidation intermediates • Further Investigation Required: • Chamber study yields overestimate yields at low NOx • Chamber study yields performed at room temperature  chemistry at cold T? • Do very reactive BVOCs inferred over forest canopies [Goldstein et al., 2004] produce appreciable SOA? • Do models over-estimate scavenging? Oxidation by OH  water-soluble products dissolve into cloud droplets Evaporation VOC

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

  29. ORGANIC CARBON AEROSOL Cloud Processing SOA: ?? TgC/yr OC Nucleation or Condensation ROG Heterogeneous Reactions Oxidation by OH, O3, NO3 FF: 45-80 TgC/yr BB: 10-30 TgC/yr Monoterpenes Isoprene Aromatics Direct Emission Fossil Fuel Biomass Burning BIOGENIC SOURCES ANTHROPOGENIC SOURCES

  30. ACKNOWLEDGEMENTS CO-AUTHORS • Daniel Jacob (Harvard), Rokjin Park (Harvard), Becky Alexander (formerly Harvard, now U of Washington), Duncan Fairlie (Harvard/Langley), Bob Yantosca (Harvard), Allen Chu (GSFC), Lynn Russell (Scripps), Barry Huebert (U of Hawaii), John Seinfeld (Caltech), Hong Liao (Caltech), Rodney Weber (Georgia Tech) SCIENCE TEAMS/CAMPAIGNS • The ACE-Asia Science Team • The TRACE-P Science Team • The MODIS Science Team • The MOPITT Science Team FUNDING: • NASA Earth System Science Fellowship and ACMAP • Natural Science and Engineering Research Council of Canada

  31. SUMMARY TRANSPACIFIC TRANSPORT OF ANTHROPOGENIC AEROSOLS • Annual Asian contributions to sulfate in the W US exceed the “natural” visibility objectives of the EPA Regional Haze Rule [Park et al., 2004] • During the spring (2001) ¼ of the sulfate observed at ground site in the NW US comes from Asia (0.18 μgm-3± 50%) • MODIS and ground observations corroborate the transpacific transport of aerosols simulated by GEOS-Chem, despite quantitative differences in observed and simulated AOD ORGANIC CARBON AEROSOL • Organic carbon aerosol observed in the FT off of Asia (~4 μgm-3) during spring 2001 is a factor of 10-100 higher than currently simulated by a global model • Concentrations of OC are also underestimated over NA during summer 2004 • These discrepancies highlight an incomplete understanding of formation and loss processes of OC and SOA in the troposphere • The high loading of OC aerosol in the FT is likely to have important implications for intercontinental transport and radiative forcing

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