BIOGENIC AEROSOL
اسلاید 1: BIOGENIC AEROSOL: SECONDARY ORGANIC AEROSOL (SOA) PRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP)
اسلاید 2: THE IMPORTANCE OF ORGANIC AEROSOL[Zhang et al., 2007]Sulfate Organics Organic material contributes 20-50% of the total fine aerosol mass at continental mid-latitudes [Saxena and Hildemann, 1996; Putaud et al., 2004] and as much as 90% in the tropical forested areas [Andreae and Crutzen, 1997; Talbot et al., 1988; 1990; Artaxo et al., 1988; 1990; Roberts et al., 2001]
اسلاید 3: CloudProcessingORGANIC CARBON AEROSOLSemi-VolatilesOxidation by OH, O3, NO3Direct EmissionFossil Fuel Biomass BurningMonoterpenesSesquiterpenesNucleation or ReversibleCondensationAromaticsIsopreneSecondary Organic AerosolPrimary Organic Aerosol
اسلاید 4: TOPICS FOR TODAYWhat are secondary organic aerosol?How do we model SOA? What are the estimated global budgets?What are primary biological aerosol particles?What do we think drives these emissions?What are the challenges in understanding biogenic organic aerosol budgets?How might SOA and PBAP be affected by climate change?
اسلاید 5: SECONDARY ORGANIC AEROSOL PRODUCTIONVOC EmissionsOxidation Reactions(OH, O3,NO3)Nucleation (oxidation products)GrowthCondensation on pre-existing aerosolOver 500 reactions to describe the formation of SOA precursors, ozone, and other photochemical pollutants [Griffin et al., 2002; Griffin et al., 2005; Chen and Griffin, 2005]
اسلاید 6: [Lunden et al., 2006]FINE PARTICLE GROWTH AT BLODGETT FOREST“Banana Plot”
اسلاید 7: GAS/PARTICLE PARTITIONING THEORYA1,A2,...,AnVOC + oxidant P1, P2, …PnG1, G2, …GnAbsorptivePartitioning TheoryM0 = pre-existing OC aerosolR=gas constant; T=temperature; p0i = vapour pressure, MWom=molecular weight of aerosols; i=activity coefficient in organic phase[Pankow, 1994]
اسلاید 8: Isoprene (C5H8)Monoterpenes(C10H16)Sesquiterpenes (C15H24)WHICH VOC’s ARE IMPORTANT SOA PRECURSORS?Anthropogenic SOA-precursors = aromatics (emissions are 10x smaller) Three factors:Atmospheric AbundanceChemical reactivityThe vapour pressure (or volatility) of its products
اسلاید 9: COMPARING SOA POTENTIALSEDGAR 1990 Emissions (Aromatics) and GEIA (Isoprene/Monoterpenes)Terpenoids: Griffin et al., 1999:Photo-oxidation: Y=1.6-84.5%NO3 oxidation: Y=12.5-89.1%O3 oxidation: Y=0-18.6%Isoprene: Kroll et al., 2005Photo-oxidation (OH): Y=0.9-3%Aromatics: Ng et al., 2007High NOx: Y=4-28%Low NOx: Y=30-36%
اسلاید 10: TOPICS FOR TODAYWhat are secondary organic aerosol?How do we model SOA? What are the estimated global budgets?What are primary biological aerosol particles?What do we think drives these emissions?What are the challenges in understanding biogenic organic aerosol budgets?How might SOA and PBAP be affected by climate change?
اسلاید 11: MODELING SOA: EXPLICIT CHEMISTRY (APPROACH #1) Using mechanistic description of chemistry coupled to partitioning. Captures hundreds of species and reactions (e.g. Master Chemical Mechanism, Leeds). Often reactions and rates have not been measured but are extrapolated from known chemistry (by analogy).These authors previously found that they needed to increases partitioning by a factor of 5-80 with the MCM to match aromatic SOA formation at the EUPHORE chamber [Johnson et al., 2004; 2005].[Johnson et al., 2006]To get this agreement:Add 0.7 µg/m3 bkgdIncrease partitioning coefficients by factor of 500Example: TORCH 2003 campaign in rural UK
اسلاید 12: MODELING SOA: 2-PRODUCT MODEL (APPROACH #2) Unknown products, so lump products into 1=high volatility and 2=low volatility Fit yields/partitioning parameters (a’s K’s) from smog chamber observationsUsed in most global/regional models Example: Global budget of biogenic SOA SOA parameterization (reversible partitioning)VOCi + OXIDANTj ai,jP1i,j + ai,jP2i,jAi,jGi,jPi,jEquilibrium (Komi,j) also f(POA)[Chung and Seinfeld, 2002]SOA from monoterpenes, sesquiterpenes and OVOCs estimated to contribute ~15% of OA burden
اسلاید 13: MODELING SOA: VOLATILITY BASIS SET (APPROACH #3) Expand the 2-product model to consider many volatility “bins” Allows chemistry/physics to move organic matter along a continuum physically attractive Loss of chemical identity complicates estimates of “mean molecular weights” and radiative forcingExample: PMCAMx (summer 2001)C* = saturation vapour pressurevolatility[Donahue et al., 2005][Lane et al., 2008]
اسلاید 14: CURRENT ESTIMATES: GLOBAL BUDGETS OF SOA[Heald et al., 2008] SOA Production Tg yr-1Isoprene14.4Monoterpenes8.7Sesquiterpenes2.1OVOC1.6Aromatics3.5TOTAL30.3POA Emission: 50-100 Tg yr-1SOA ~ 25-50% of OA source in models(mostly biogenic)Annual mean zonal distribution of SOA (2000)GEOS-Chem model global annual budget[Henze et al., 2008]
اسلاید 15: TOPICS FOR TODAYWhat are secondary organic aerosol?How do we model SOA? What are the estimated global budgets?What are primary biological aerosol particles?What do we think drives these emissions?What are the challenges in understanding biogenic organic aerosol budgets?How might SOA and PBAP be affected by climate change?
اسلاید 16: PRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP)POLLENBACTERIAVIRUSESFUNGUSALGAEPLANTDEBRISJaenicke [2005] suggests may be as large a source as dust/sea salt (1000s Tg/yr)May act as CCN and IN [Diehl et al., 2001; Bauer et al., 2003; Christiner et al., 2008]
اسلاید 17: PBAP: PRESENT-THROUGHOUT THE YEAR, IN URBAN AND RURAL LOCATIONSMainz, Germany (1990-1998)Lake Baikal, Russia (1996-1997)Particles > 0.2 m, stained with protein dyeNo clear seasonality: multiple PBAP sourcesPBAP # fraction = 5-50%[Jaenicke, 2005]
اسلاید 18: PBAP: PARTICLES ACROSS THE SIZE RANGEFrom Andi Andreae (unpublished data)Dominates the coarse mode (pollens, debris, etc)May also make important contribution to fine mode aerosol
اسلاید 19: MARINE PBAP[O’Dowd et al., 2008]Primary marine aerosol from “bubble bursting mechanism” associated with sea spray, correlated with periods of biological activity.Chlorophyll AMace Head, IrelandOceanSurfactant Layer (with Organics)WINDSea-spray emissionof sea salt (and OC)
اسلاید 20: TOPICS FOR TODAYWhat are secondary organic aerosol?How do we model SOA? What are the estimated global budgets?What are primary biological aerosol particles?What do we think drives these emissions?What are the challenges in understanding biogenic organic aerosol budgets?How might SOA and PBAP be affected by climate change?
اسلاید 21: WHAT MIGHT DRIVE PBAP EMISSIONS/CONCENTRATIONS?WindTemperature Biological activityVegetation coverHumidity / wetnessAnthropogenic ActivityAtmospheric release/dispersionCan affect release (surface bonding), proxy for growing season?Stimulates sourceSource = vegetation, soil, decaying matterFacilitates release (e.g. spores)Industrial/municipal facilities e.g. spores/molds in old buildings, sewage treatment plants, textile mills[Jones and Harrison, 2004]
اسلاید 22: TOPICS FOR TODAYWhat are secondary organic aerosol?How do we model SOA? What are the estimated global budgets?What are primary biological aerosol particles?What do we think drives these emissions?What are the challenges in understanding biogenic organic aerosol budgets?How might SOA and PBAP be affected by climate change?
اسلاید 23: MEASURING OC IN THE ATMOSPHEREAmbient AirDenuder toremove gas-phaseorganicsQuartz Filter (#1)Backup (#2)(to capture OCevaporated from filter #1)Hamilton et al. [2004]: over 10 000 organic compounds detected in a single PM2.5 sample collected in London, England Thermal Optical analysis to determine OC ConcentrationCHALLENGE: To measure suite of compounds classified as organic carbon, without artifacts from the gas phase
اسلاید 24: INTERPRETING ORGANIC AEROSOL MEASUREMENTSExample from Pittsburg Air Quality Study [Cabada et al., 2004]EC/OC ratio for primaryemissions are well-correlated(triangles).Deviations from the slopeare indicative of a secondaryOC source (squares).Uncertainties: changing EC/OC emission ratios for sources mixing of air massesEC=elemental carbon (direct emission only, primarily fossil fuel)CHALLENGE: once OA measured, can we separate POA and SOA?
اسلاید 25: INTERPRETING ORGANIC AEROSOL MEASUREMENTS AEROSOL MASS SPECTROMETER (AMS)Reduce complexity of observed spectra to 2 signals:[Zhang et al., 2005]~2/3 of OC is SOA (in urban site!)m/z 44: oxygenated organic aerosol SOAm/z 57: hydrocarbonlike organic aerosol POA
اسلاید 26: EmittedEscaped Reacted + O3+ OH+ O3+ O3Oxidation ProductsAbove-Canopy Flux MeasurementsBranch Enclosures: Actual EmissionsOxidation Experiments & In-Canopy GradientSCALES OF MEASUREMENTCourtesy: Anita Lee (Berkeley, now EPA)
اسلاید 27: DISAGREEMENT BETWEEN MODELS AND OBSERVATIONS[Volkamer et al., 2006]Measurements are challenging, cannot distinguish POA & SOA, issues such as collection efficiencies, artifacts can be important.Models are simplified treatments (e.g. 2 product model)Models are based on lab data (applicability to ambient conditions?)
اسلاید 28: TOPICS FOR TODAYWhat are secondary organic aerosol?How do we model SOA? What are the estimated global budgets?What are primary biological aerosol particles?What do we think drives these emissions?What are the challenges in understanding biogenic organic aerosol budgets?How might SOA and PBAP be affected by climate change?
اسلاید 29:
اسلاید 30: CloudProcessingHOW MIGHT BIOGENIC OA CHANGE IN THE FUTURE? Semi-VolatilesOxidation by OH, O3, NO3Direct EmissionFossil Fuel Biomass BurningMonoterpenesSesquiterpenesNucleation or ReversibleCondensationAromaticsIsopreneSecondary Organic AerosolPrimary Organic AerosolT, Mo
اسلاید 31: PLUS: FEEDBACKS ON THE BIOSPHERE Changing aerosol burden affects clouds/precip/chemical deposition and radiation changing SOA sources (BVOC)Change in Emissions: -4510 mg m-2 h-1 to 5174 mg m-2 h-1Christine Wiedinmyer, NCAR
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