FINE AEROSOL COMPOSITION IN NORTH AMERICA Annual mean PM 2.5 concentrations (NARSTO, 2004) Current air quality standard is 15  g m -3

SULFATE-NITRATE-AMMONIUM AEROSOLS IN U.S. (2001) Highest concentrations in industrial Midwest (coal-fired power plants) SulfateNitrate Ammonium Acidity

Ammonia and NO x emissions in the US (2006) Zhang et al. [2012]

Distributions of HNO 3 (g) and NO 3 - (aerosol) in surface air HNO 3 (g) NO 3 - (aerosol) EPA network data for 2006 Zhang et al. [2012]

FORMATION OF SULFATE-NITRATE-AMMONIUM AEROSOLS Sulfate always forms an aqueous aerosol Ammonia dissolves in the sulfate aerosol totally or until titration of acidity, whichever happens first Nitrate is taken up by aerosol if (and only if) excess NH 3 is available after sulfate titration HNO 3 and excess NH 3 can also form a solid aerosol if RH is low Thermodynamic rules: Highest concentrations in industrial Midwest (coal-fired power plants) Conditionaerosol pHLow RHHigh RH 2[S(VI)] > [N(-III)]acidH 2 SO 4 nH 2 O, NH 4 HSO 4, (NH 4 ) 2 SO 4 (NH 4 +, H +, SO 4 2- ) solution 2[S(VI)] ≤ [N(-III)]neutral(NH 4 ) 2 SO 4, NH 4 NO 3 (NH 4 +, SO 4 2-, NO 3 - ) solution

U.S. SO 2 EMISSIONS Sulfur emissions, Tg a GLOBAL UNITED STATES

Observation of SO 2 point sources in US by OMI oversampling SO2 point sources, OMI SO 2 (3 km oversampling) 3 km-resolution data enables analysis of SO 2 emission trends, SO 2 atmospheric lifetime AQAST PI: De Foy

SO 2 columns observed from SCIAMACHY SAA

GOME and SCIAMACHY SO 2 over China Large increase in SO 2 loading observed from 2000 to 2007 Turnover in 2007 Decrease to 2003 / 2004 levels but now increasing again. Result of legislation requiring flue-gas desulphurization of power plants Not all power plants have been equipped other sources are on the rise Volcanic eruption

Kasatochi eruption as seen in GOME-2 SO 2 After some smaller SO 2 emissions, large eruption on August 8, 2008 SO 2 rapidly distributes over the NH GOME-2 integrated SO 2 column indicates more than 1 Tg total SO 2 emission Kasatochi volcano Altitude: 314 m Latitude: 52.16°N Longitude: ° W

OBSERVED TITRATION OF SO 2 BY H 2 O 2 IN CLOUD First aircraft observations by Daum et al. [1984]

WORLDWIDE MEASUREMENTS OF FINE AEROSOL COMPOSITION

CARBONACEOUS AEROSOL SOURCES IN THE U.S. ORGANIC CARBON (OC) 2.7 Tg yr -1 BLACK CARBON (BC) 0.66 Tg yr -1 Annual mean concentrations (2001) BC OC Park et al. [2006]

Long-term trends in BC and OC aerosol over the US Annual mean concentrations National trends Observed Model Leibensperger et al. [2011]

RADIATIVE FORCING FROM BLACK CARBON (BC) IPCC [2007]

BC is emitted by incomplete combustion “BC” or “soot” is optically defined and includes both graphitic elemental carbon (EC) and light-absorbing heavy organic matter Diesel engines are large BC sources Freshly emitted BC particle

Atmospheric aging and scavenging of BC Emission Hydrophobic BC resistant to scavenging coagulation gas condensation Hydrophilic BC coated with sulfate, nitrate Scavenging Aging time scale τ ~ 1 d Implications for BC export from source continents: OCEAN aging scavenging Hydrophobic BC aging long-range transport FREE TROPOSPHERE BOUNDARY LAYER

BC and OC aerosol during ARCTAS aircraft campaign (spring 2008) Wang et al. [2011]

ORGANIC AEROSOL IN STANDARD GEOS-Chem MODEL fuel/industry open fires OH, O 3,NO 3 SOGSOA POA K vegetation fuel/industry open fires 700 isoprene terpenes oxygenates… 30 alkenes aromatics oxygenates… alkanes alkenes aromatics… VOC EMISSIONPRIMARY EMISSION VOC Global sources in Tg C y -1 secondary formation SOA ≡ secondary organic aerosol POA ≡ primary organic aerosol

TERPENES Terpenes are biogenic hydrocarbons produced in plants by combination of isoprene units (C 5 H 8 ) Monoterpenes: C 10 H 16 β-pinene Sesquiterpenes: C 15 H 24 δ-cadinene

SOA MODELING AS GAS-AEROSOL EQUILIBRIUM VOC oxidation generates semi-volatile products: …which then partition between the gas and aerosol phase: where the partitioning coefficient is given by …and is a strong function of temperature. Values of  and p 0 are fitted to smog chamber data Chung and Seinfeld, 2002 M o is the mass concentration of pre-existing organic aerosol

SOA MODELING USING VOLATILITY BASIS SETS Partition semi-volatile VOCs (SVOCs) between aerosol and gas: Aerosol fraction for SVOC i Define SVOCs by their stability class: Donahue et al. [2006]

SOA VOLATILITY BASIS SET: EFFECT OF DILUTION Donahue et al. [2006]

SOA VOLATILITY BASIS SET: CHEMICAL AGING Donahue et al. [2006] As VOCs go through successive oxidation steps, products become more oxygenated and less volatile, but eventually smaller and more volatile

IMPLEMENTING OC VOLATILITY CLASSES IN GEOS-Chem Pye and Seinfeld [2010] Combustion “Primary” OC is actually semi-volatile Mean wintertime OC concentrations: IMPROVE data shown as circles

POSSIBLE MECHANISMS FOR DICARBONYL SOA FORMATION GASAQUEOUS Oligomers OH Organic acids K H * ~ 10 5 M atm -1 Ervens et al. [2004] Crahan et al. [2004] Lim et al. [2005] Carlton et al. [2006, 2007] Warneck et al. [2005] Sorooshian et al. [2006, 2007] Altieri et al. [2006, 2008] Schweitzer et al. [1998] Kalberer et al. [2004] Liggio et al. [2005a,b] Hastings et al. [2005] Zhao et al. [2006] Loeffler et al. [2006] glyoxal K H * ~ 10 3 M atm -1 methylglyoxal oxidation oligomerization

GLYOXAL/METHYLGLYOXAL FORMATION FROM ISOPRENE GEOS-Chem mechanism based on MCM v3.1 Fu et al. [JGR, 2008] 6%25% molar yields

Van Krevelen diagram for chemical aging of organic material Heald et al. [2010]

Van Krevelen diagram: application to organic aerosol Heald et al. [2010] -1 slope suggests aging by adding of –COOH functionalities