Secondary Organic Aerosols: What we know and current CAM treatment Chemistry-Climate Working Group Meeting, CCSM March 22, 2006 Colette L. Heald

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: TgC/yr BB: TgC/yr Secondary Organic Aerosol (SOA): 8-40 TgC/yr *Numbers from IPCC [2001]

IN THE LAB: SMOG CHAMBER EXPERIMENTS Teflon Chamber 20-30°C Oxidant (OH, O 3, NO 3 ) High NOx VOC eg.  -pinene dry seed particles eg. (NH 3 ) 2 SO 4 SOA formation Biogenic terpenes: yield 2-67% [Griffin et al., 1999] Wall loss Issues: 1.High VOC concentrations 2.High oxidant and NOx concentrations 3.Relatively high (generally fixed) T

Two Product Model [Odum et al., 1997]: ROG i + OXIDANT j   i,j P1 i,j +  i,j P2 i,j once formed the semi-volatile reaction products (P) will partition b/w gas and aerosol phase (as governed by the equilibrium partition coefficient (K om ) fitting parameters (  ’s and K’s) from smog chamber data partition coefficients are temperature sensitive (use Clausius-Clapeyron eqn) at each time-step solve for equilibrium IN A MODEL: SOA PARAMETERIZATION [Chung and Seinfeld, 2002] [G] =product (gas) or SOG [A] = product (aerosol) or SOA M o = concentration of total organic aerosol  H= enthalpy of vaporization ROG = 5 biogenic HC classes (terpenes and ORVOCs) OXIDANT = OH, O 3, NO 3  Carry both gas and aerosol phase products as tracers 

IN CAM: SIMPLIFIED 2-PRODUCT FORMULATION [Lack et al., 2004] For < 0.2 μg/m 3 pre-existing OC: use bulk yield For > 0.2 μg/m 3 : partition using two product model take parameters from smog chamber data ultimate yield calculated as: No temperature dependence on partitioning  corrected Add newly formed SOA to pre-existing ROG = terpenes (C 10 H 16 ), toluene and big alkanes (> heptane) OXIDANTS = OH, O 3, NO 3  Carry only lumped SOA product  ADVANTAGE: one SINGLE tracer (for as many precursors as we want) DISADVANTAGE: not representing equilibrium process QUESTION: Is additional complexity warranted?

ACE-ASIA: OC AEROSOL MEASUREMENTS IN THE FREE TROPOSPHERE Mean Observations Mean Simulation (GEOS-Chem [Park et al., 2003]) Observations + High Levels of OC were observed in the FT during ACE-Asia by 2 independent measurement techniques. We cannot simulate this OC with current models [Heald et al., 2005]. Seinfeld group Huebert group Russell group (ACE-Asia aircraft campaign conducted off of Japan during April/May 2001)

UNDERESTIMATE OF OC AEROSOL DURING ICARTT NOAA ITCT-2K4 flight tracks (R. Weber’s PILS instrument aboard) Observations GEOS-Chem Simulation Note: biomass burning plumes were removed OC aerosol underestimate observed over North America as well [Heald et al., in prep]. SOA WSOMC OMC (=POA+SOA) OMC=organic molecular carbon (=1.4xOC) WS=water soluble (10-80% of total OC, primarily SOA)

Evap ISOPRENE AS A SOURCE OF SOA Pandis et al., 1991 NO SOA observed Kroll et al., 2005 Yield = % Edney et al., 2005 NO SOA observed unless SO 2 present Claeys et al., 2004 Observed tetrols (ox product of isoprene) Propose: acid-catalysed reaction w/ H 2 O 2 Matsunaga et al., 2005 Observed ox products of isoprene in particulate phase. Propose: polymerization Lim et al., 2004 Cloud processing of Isoprene supported by lab experiments Smog Chamber Smog Chamber Smog Chamber Ox VOC Isoprene is the second most abundant hydrocarbon emitted to the atmosphere (~500 Tg/yr). Even with a modest yield this could be an important source of SOA.

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: TgC/yr BB: TgC/yr Secondary Organic Aerosol (SOA): 8-40 TgC/yr *Numbers from IPCC [2001]

ORGANIC CARBON AEROSOL ROG Oxidation by OH, O 3, NO 3 Direct Emission Monoterpenes Nucleation or Condensation Aromatics OC Isoprene Cloud Processing FF: TgC/yr BB: TgC/yr SOA: ?? TgC/yr Fossil Fuel Biomass Burning ANTHROPOGENIC SOURCESBIOGENIC SOURCES Heterogeneous Reactions

SOA FORMATION: PROCESSES TO CONSIDER HC + oxidant + Condensation 1.Multiple oxidation steps (explicit chemistry) 2.Isoprene as a source of SOA [Kroll et al., 2005; Henze et al., submitted] 3.Effect of NOx concentrations  LAB 4.Temperature-dependence of formation  LAB 5.Uptake on inorganic aerosols  LAB 6.Polymerization reactions  LAB 7.Heterogeneous reactions  LAB 8.Cloud processing Current plan for CAM: 1.Add isoprene as a source of SOA using 2-product framework 2.Put latest MEGAN biogenic emission model in CLM to drive CAM 3.Look at sensitivity of SOA formation to climate change