organic carbon aerosol colette l. heald university of california, berkeley noaa summer institute,...
Post on 15-Jan-2016
220 Views
Preview:
TRANSCRIPT
Organic Carbon Aerosol
Colette L. Heald
University of California, Berkeley
NOAA Summer Institute, Steamboat Springs, COJuly 12, 2006
CURRENT UNDERSTANDING: SOURCES OF ORGANIC CARBON AEROSOL
ReactiveOrganicGases
Oxidation by OH, O3, NO3
Direct Emission
Fossil Fuel Biomass Burning
Monoterpenes
Nucleation or Condensation
Aromatics
ANTHROPOGENIC SOURCESBIOGENIC SOURCES
OC
FF: 45-80 TgC/yrBB: 10-30 TgC/yr
Secondary Organic Aerosol (SOA): 8-40 TgC/yr
*Numbers from IPCC [2001]
Formation and Transport
Emissions:1. Anthropogenic2. Natural/Biogenic
ORGANIC AEROSOLS: AIR QUALITY, CHEMISTRY AND CLIMATE
Air Quality Impacts:1. Visibility
2. Health
Climate Forcing1. Direct: Scatter solar radiation2. Indirect: ↑ cloud albedo
↑ cloud lifetime
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
ACE-ASIA: FIRST OC AEROSOL MEASUREMENTS IN THE FREE TROPOSPHERE
Mean ObservationsMean SimulationObservations+
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 ChemicalTransport model
[Heald et al., 2005]
[Mader et al., 2002] [Huebert et al., 2003] [Maria et al., 2003]
CONTRAST: OTHER AEROSOLS IN ASIAN OUTFLOW
Model simulates both the magnitude and profile of sulfate and elemental carbon (EC) during ACE-Asia
Mean ObservationsMean Simulation (GEOS-Chem)
Scavenging ScavengingSecondaryproduction
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.
SECONDARY ORGANIC AEROSOL
Biogenic VOCs(eg. monoterpenes)
ReactiveOrganic Gases
Oxidation by OH, O3, NO3
SecondaryOrganic Aerosol
Condensation of low vapour pressure ROGs on pre-existing aerosol
Simulated April Biogenic SOA
FT observations ~ 4g/m3
Simulated SOA far too small!
SOA parameterization [Chung and Seinfeld, 2002]
VOCi + OXIDANTj i,jP1i,j + i,jP2i,j
Parameters (’s K’s) from smog chamber studies
Ai,j
GGi,ji,j
Pi,jEquilibrium (Komi,j) also f(POA)
SEVERAL STUDIES SUGGESTING UNDERESTIMATE OF SOA
[Volkamer et al., 2006]
Global underestimate in SOA?
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.
ObservedSimulated
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]
WHAT DON’T WE UNDERSTAND ABOUT SOA FORMATION?
ROG
Oxidation by OH, O3, NO3
Direct Emission
Monoterpenes
Nucleation or Condensation
Aromatics
OC
Isoprene
CloudProcessing
FF: 45-80 TgC/yrBB: 10-30 TgC/yr
SOA: ?? TgC/yr
Fossil Fuel Biomass Burning
ANTHROPOGENIC SOURCESBIOGENIC SOURCES
Heterogeneous ReactionsAdditionalPrecursors
1. Production moreefficient at low NOx2. Multi-step oxidation
New formation pathways
CARBON CYCLE AND POTENTIAL RADIATIVE IMPLICATIONS
VOC EMISSIONS500-1000 TgC/yr
[IPCC, 2001]
DISSOLVED ORGANIC CARBON
IN RAINWATER430 TgC/yr
[Wiley et al., 2000]
OC AEROSOL1 µg/m3 from 2-7 km globally = 105 TgC/yr
4 μg/m3 (ACE-Asia)AOD @ 50% RH: 0.057
TOA Radiative Forcing = -1.2 W/m2
CURRENT WORK: HOW WILL SOA FORMATION RESPOND TO A FUTURE CLIMATE?
Biogenic Emissionsof precursors:T/light/moisture
Anthropogenic Emissions:Increasing aromatic emissionsMore 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)
ACKNOWLEDGEMENTS
Daniel Jacob, Rokjin Park, Solène Turquety, Rynda Hudman
Barry HuebertLynn Russell John Seinfeld, Hong Liao
Rodney Weber,Amy SullivanRick Peltier
ITCT-2K4 Science Team
Hosts: Inez Fung & Allen Goldstein
top related