1 / 32

Secondary Organic Aerosols: What we know and current CAM treatment

Secondary Organic Aerosols: What we know and current CAM treatment. Colette L. Heald (heald@atmos.berkeley.edu). Chemistry-Climate Working Group Meeting, CCSM March 22, 2006. ORGANIC CARBON AEROSOL. *Numbers from IPCC [2001]. Secondary Organic Aerosol (SOA): 8-40 TgC/yr. Reactive

rusti
Download Presentation

Secondary Organic Aerosols: What we know and current CAM treatment

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Secondary Organic Aerosols:What we know and current CAM treatment Colette L. Heald (heald@atmos.berkeley.edu) Chemistry-Climate Working Group Meeting, CCSM March 22, 2006

  2. 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

  3. IN THE LAB: SMOG CHAMBER EXPERIMENTS Teflon Chamber 20-30°C Oxidant (OH, O3, NO3) High NOx VOC eg. a-pinene SOA formation dry seed particles eg. (NH3)2SO4 Wall loss Biogenic terpenes: yield 2-67% [Griffin et al., 1999] • Issues: • High VOC concentrations • High oxidant and NOx concentrations • Relatively high (generally fixed) T

  4. IN A MODEL: SOA PARAMETERIZATION [Chung and Seinfeld, 2002] • Two Product Model [Odum et al., 1997]: ROGi + OXIDANTj  ai,jP1i,j + ai,jP2i,j • once formed the semi-volatile reaction products (P) will partition b/w gas and aerosol phase (as governed by the equilibrium partition coefficient (Kom) • fitting parameters (a’s and K’s) from smog chamber data • partition coefficients are temperature sensitive (use Clausius-Clapeyron eqn) • at each time-step solve for equilibrium [G] =product (gas) or SOG [A] = product (aerosol) or SOA Mo = concentration of total organic aerosol DH= enthalpy of vaporization ROG = 5 biogenic HC classes (terpenes and ORVOCs) OXIDANT = OH, O3, NO3  Carry both gas and aerosol phase products as tracers 

  5. IN CAM: SIMPLIFIED 2-PRODUCT FORMULATION[Lack et al., 2004] • For < 0.2 μg/m3 pre-existing OC: use bulk yield • For > 0.2 μg/m3: 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 (C10H16), toluene and big alkanes (> heptane) OXIDANTS = OH, O3, NO3  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?

  6. Mean Observations Mean Simulation (GEOS-Chem [Park et al., 2003]) 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 current models [Heald et al., 2005].

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

  8. ISOPRENE AS A SOURCE OF SOA Pandis et al., 1991 NO SOA observed Kroll et al., 2005 Yield = 0.9-3.0% Edney et al., 2005 NO SOA observed unless SO2 present Smog Chamber Smog Chamber Smog Chamber Claeys et al., 2004 Observed tetrols (ox product of isoprene) Propose: acid-catalysed reaction w/ H2O2 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 Ox VOC Evap 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.

  9. 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

  10. 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

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

  12. SOx CONCENTRATIONS: IMPROVE SITES (1988-2004) CAM wetdep Mozart wetdep SO2 Sulfate concentrations in the US overestimated with Mozart wetdep SO4

  13. SULFATE COMPARISONS: U MIAMI SITES (1981-1998) Mozart wetdep CAM wetdep μg/m3 Sulfate concentrations globally reasonable for both simulations (less bias with CAM wetdep)

  14. OC CONCENTRATIONS: IMPROVE SITES (1988-2004) Mozart wetdep CAMwetdep OC comparison with observations over the US not definitive…

  15. AEROSOL OPTICAL DEPTH COMPARISON (2001/2005) Less wet deposition in Mozart increases AOD  better match with satellites over water, but overestimate over land

  16. AOD COMPARISONS: AERONET SITES (1992-2005) Mozart wetdep CAMwetdep Mozart wetdep CAMwetdep CAM wet deposition better representation of magnitude and seasonality at all sites. Note that both simulations show excessive aerosol transport over oceans.

  17. SEASONAL CYCLE: AOD COMPARISONS LAND OCEAN

  18. FORMATION OF SOA VOC + ox  P1, P2, …Pn • G1,G2,...,Gn AQ1,AQ2,...,AQn A1,A2,...,An Partitioning Theory Henry’s Law and Dissociation Hi = giaqAQi/Gi AQi AQi-AQi2- Ai / Mo RT Kom,i = ~ Gi poL,i MWomgi Griffin et al. (2003)

  19. FIRST SUGGESTIONS OF HIGH ORGANIC CARBON AEROSOL CONCENTRATIONS IN THE FT 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]

  20. Mean Observations Mean Simulation (GEOS-Chem) ACE-ASIA: MODEL REPRODUCES OTHER AEROSOL PROFILES 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?

  21. ACE-ASIA: SECONDARY ORGANIC AEROSOL UNDERESTIMATED? SOA is a good candidate: condense more easily with colder temperature AND be produced in the FT (escape scavenging) 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 Simulated biogenic SOA far too small!

  22. 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!

  23. 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 [Claeys et al., 2004; 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.

  24. 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 may be much lower [Sellegri et al., 2003]. Observations GEOS-Chem Simulation GEOS-Chem Simulation (with scavenging e=0.14) ITCT 2K4 OMC A large decrease in scavenging efficiency increases OMC concentrations throughout the troposphere. To what degree are OC aerosols internally mixed?

  25. CLIMATOLOGICAL DIRECT EMISSIONS FROM ASIA % of Global Emissions 31% 41% 32% 20% 38% 20% *Anthropogenic is primarily FF (except for NH3 where it includes domesticated animals, humans), also includes small contributions from fertilizer (NOx, NH3) and aircraft (SOx, NOx)

  26. CLIMATOLOGICAL DIRECT EMISSIONS FROM NORTH AMERICA % of Global Emissions 8% 8% 20% 22% 9% 1% *Anthropogenic is primarily FF (except for NH3 where it includes domesticated animals, humans), also includes small contributions from fertilizer (NOx, NH3) and aircraft (SOx, NOx)

  27. 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] ACE-ASIA OC: IMPLICATIONS FOR TRANSPACIFIC TRANSPORT AND RADIATIVE FORCING 4 ug/sm3 (ACE-Asia) @ 50% RH TOA Radiative Forcing = -1.2 W/m2 ASIA NORTH AMERICA PACIFIC

  28. 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 [Wiley et al., 2000] VOC EMISSIONS 500-1000 TgC/yr [IPCC, 2001] [Heald et al., 2005a]

  29. WET DEPOSITION IN GEOS-CHEM [Liu et al., 2001] 1. CONVECTIVE UPDRAFTS 2. RAINOUT Depends on fraction of grid square experiencing precipitation (global avg = 2.5% stratiform, 0.4% convective) dz 3. WASHOUT Fraction lost during ascent = adz Scavenging efficiency (a) = 4x10-4 m-1 fscav=1-e-aDz  40% scavenged in 1 km Washout rate constant = 0.1 per mm precip applied to max fraction of grid square experiencing precipitation above.

  30. BIOGENIC SOA

More Related