BIOGENIC AEROSOL: SECONDARY ORGANIC AEROSOL (SOA) PRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP)

THE IMPORTANCE OF ORGANIC AEROSOL Sulfate Organics [Zhang et al., 2007] 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]

ORGANIC CARBON AEROSOL Secondary Organic Aerosol Cloud Processing Semi- Volatiles Nucleation or ReversibleCondensation Primary Organic Aerosol Oxidation by OH, O3, NO3 Monoterpenes Sesquiterpenes Aromatics Isoprene Direct Emission Fossil Fuel Biomass Burning

TOPICS FOR TODAY What 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?

SECONDARY ORGANIC AEROSOL PRODUCTION VOC Emissions Nucleation (oxidation products) Oxidation Reactions (OH, O3,NO3) Growth Condensation on pre-existing aerosol Over 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]

FINE PARTICLE GROWTH AT BLODGETT FOREST “Banana Plot” [Lunden et al., 2006]

GAS/PARTICLE PARTITIONING THEORY VOC + oxidant  P1, P2, …Pn M0 = pre-existing OC aerosol A1,A2,...,An G1, G2, …Gn Absorptive Partitioning Theory [Pankow, 1994] R=gas constant; T=temperature; p0i = vapour pressure, MWom=molecular weight of aerosols; i=activity coefficient in organic phase

WHICH VOC’s ARE IMPORTANT SOA PRECURSORS? Isoprene (C5H8) Three factors: Atmospheric Abundance Chemical reactivity The vapour pressure (or volatility) of its products Monoterpenes(C10H16) Sesquiterpenes (C15H24) Anthropogenic SOA-precursors = aromatics (emissions are 10x smaller)

COMPARING SOA POTENTIALS EDGAR 1990 Emissions (Aromatics) and GEIA (Isoprene/Monoterpenes) Species Global (Tg/yr) Aromatics Benzene Toluene Xylene Other 21.7 5.8 6.7 4.5 4.7 SOA pot’l (15%) 3.2 Monoterpenes 130.6 SOA pot’l (10%) 13.1 Sesquiterpenes ? SOA pot’l (75%) Isoprene 341 SOA pot’l (3%) 10.2 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., 2005 Photo-oxidation (OH): Y=0.9-3% Aromatics: Ng et al., 2007 High NOx: Y=4-28% Low NOx: Y=30-36%

TOPICS FOR TODAY What 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?

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). Example: TORCH 2003 campaign in rural UK To get this agreement: Add 0.7 µg/m3 bkgd Increase partitioning coefficients by factor of 500 [Johnson et al., 2006] 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].

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 observations Used in most global/regional models SOA parameterization (reversible partitioning) VOCi + OXIDANTj  ai,jP1i,j + ai,jP2i,j Ai,j Gi,j Pi,j Equilibrium (Komi,j)  also f(POA) Example: Global budget of biogenic SOA SOA from monoterpenes, sesquiterpenes and OVOCs estimated to contribute ~15% of OA burden [Chung and Seinfeld, 2002]

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 forcing Example: PMCAMx (summer 2001) volatility C* = saturation vapour pressure [Donahue et al., 2005] [Lane et al., 2008]

CURRENT ESTIMATES: GLOBAL BUDGETS OF SOA Annual mean zonal distribution of SOA (2000) [Heald et al., 2008] GEOS-Chem model global annual budget   SOA Production Tg yr-1 Isoprene 14.4 Monoterpenes 8.7 Sesquiterpenes 2.1 OVOC 1.6 Aromatics 3.5 TOTAL 30.3 POA Emission: 50-100 Tg yr-1 SOA ~ 25-50% of OA source in models (mostly biogenic) [Henze et al., 2008]

TOPICS FOR TODAY What 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?

PRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP) BACTERIA VIRUSES POLLEN FUNGUS PLANT DEBRIS ALGAE Jaenicke [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]

PBAP: PRESENT-THROUGHOUT THE YEAR, IN URBAN AND RURAL LOCATIONS Mainz, Germany (1990-1998) Particles > 0.2 m, stained with protein dye No clear seasonality: multiple PBAP sources PBAP # fraction = 5-50% Lake Baikal, Russia (1996-1997) [Jaenicke, 2005]

PBAP: PARTICLES ACROSS THE SIZE RANGE May also make important contribution to fine mode aerosol Dominates the coarse mode (pollens, debris, etc) From Andi Andreae (unpublished data)

Surfactant Layer (with Organics) MARINE PBAP Sea-spray emission of sea salt (and OC) WIND Primary marine aerosol from “bubble bursting mechanism” associated with sea spray, correlated with periods of biological activity. Surfactant Layer (with Organics) Ocean Mace Head, Ireland Chlorophyll A [O’Dowd et al., 2008]

TOPICS FOR TODAY What 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?

WHAT MIGHT DRIVE PBAP EMISSIONS/CONCENTRATIONS? Wind Temperature Biological activity Vegetation cover Humidity / wetness Anthropogenic Activity Atmospheric release/dispersion Can affect release (surface bonding), proxy for growing season? Stimulates source Source = vegetation, soil, decaying matter Facilitates release (e.g. spores) Industrial/municipal facilities e.g. spores/molds in old buildings, sewage treatment plants, textile mills [Jones and Harrison, 2004]

TOPICS FOR TODAY What 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?

MEASURING OC IN THE ATMOSPHERE Hamilton et al. [2004]: over 10 000 organic compounds detected in a single PM2.5 sample collected in London, England CHALLENGE: To measure suite of compounds classified as organic carbon, without artifacts from the gas phase Ambient Air Denuder to remove gas-phase organics Quartz Filter (#1) Backup (#2) (to capture OC evaporated from filter #1) Thermal Optical analysis to determine OC Concentration

INTERPRETING ORGANIC AEROSOL MEASUREMENTS CHALLENGE: once OA measured, can we separate POA and SOA? Example from Pittsburg Air Quality Study [Cabada et al., 2004] EC/OC ratio for primary emissions are well-correlated (triangles). Deviations from the slope are indicative of a secondary OC source (squares). Uncertainties: changing EC/OC emission ratios for sources mixing of air masses EC=elemental carbon (direct emission only, primarily fossil fuel)

Reduce complexity of observed spectra to 2 signals: INTERPRETING ORGANIC AEROSOL MEASUREMENTS AEROSOL MASS SPECTROMETER (AMS) m/z 57: hydrocarbon like organic aerosol  POA m/z 44: oxygenated organic aerosol  SOA Reduce complexity of observed spectra to 2 signals: ~2/3 of OC is SOA (in urban site!) [Zhang et al., 2005]

SCALES OF MEASUREMENT Escaped Reacted Emitted Above-Canopy Flux Measurements Escaped + O3 + OH Oxidation Experiments & In-Canopy Gradient Oxidation Products Reacted Emitted Branch Enclosures: Actual Emissions Courtesy: Anita Lee (Berkeley, now EPA)

DISAGREEMENT BETWEEN MODELS AND OBSERVATIONS 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?) [Volkamer et al., 2006]

TOPICS FOR TODAY What 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?

HOW MIGHT BIOGENIC OA CHANGE IN THE FUTURE? Secondary Organic Aerosol Cloud Processing Semi- Volatiles Nucleation or ReversibleCondensation Primary Organic Aerosol Oxidation by OH, O3, NO3 T, Mo Monoterpenes Sesquiterpenes Aromatics Isoprene Direct Emission Fossil Fuel Biomass Burning

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-1 Christine Wiedinmyer, NCAR