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Gas and Aerosol Partitioning Over the Equatorial Pacific

Gas and Aerosol Partitioning Over the Equatorial Pacific . Wenxian Zhang April 21, 2009. In the Marine Boundary Layer…. Sea salt aerosol - Main components: Na and Cl - Large water content - Diameter larger than 0.5um - Average lifetime: 6 days (Pham et al., 1995)

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Gas and Aerosol Partitioning Over the Equatorial Pacific

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  1. Gas and Aerosol Partitioning Over the Equatorial Pacific Wenxian Zhang April 21, 2009

  2. In the Marine Boundary Layer… Sea salt aerosol - Main components: Na and Cl - Large water content - Diameter larger than 0.5um - Average lifetime: 6 days (Pham et al., 1995) - Emission rate around 1000 particles m-2 s-1 (Smith et al., 1993)

  3. In the Marine Boundary Layer… DMS (CH3-S-CH3) • Produced by marine phytoplankton • The dominant sulfur compound emitted from the oceans • Volatile in the ocean • Oxidized by OH and NO3 radicals • Exclusive source for methane sulfonic acid (MSA) and the dominant source of SO2 in the marine atmosphere MSA (CH3(O)S(O)OH) • One of the product of DMS oxidation • Non-volatile and can exist in aqueous phase • MS/NSS ratio have been studies to understand the sulfur cycle.

  4. Over the Marine Boundary Layer… • Buffer Layer • 650~1500m • Intermittent turbulence • Reduced concentration of sea salt aerosols • Free Troposphere • Less vertical mixing • Aerosol size is less than 0.5um

  5. Gas/Aerosol Partitioning α is the activity of a species, which depends on the concentration of this component Equilibrium Condition μ is the chemical potential whose difference is the cause for chemical reaction or for mass transfer from one phase to another. K is the equilibrium constant, which is highly depend on T

  6. Deliquescent Relative Humidity • The threshold RH for the solid particle to absorb water spontaneously • Depends on the particle composition

  7. ISORROPIA • A Thermodynamic equilibrium model for multiphase multicomponent inorganic aerosols • Components: Sodium, ammonium, chloride, sulfate, nitrate, and water • Possible species: Gas: NH3, HNO3, HCl, H2O Liquid: NH4,Na,H,Cl,NO3,SO4,HSO4,OH,H2O Solid:(NH4)2SO4,NH4HSO4,(NH4)3H(SO4)2,NH4NO3, NH4Cl,NaCl,NaNO3,NaHSO4,Na2SO4

  8. Three box model T=285K RH=40% • Assumptions - Lifetime of DMS is 0.5day - DMS is entirely converted to MS and NSS - tMS/tNSS=0.35 - Aerosol sulfate comes from only non – sea salt sulfate 1500m k2= 1 m2s-1 T=290K RH=90% 650m k1= 10 m2s-1 T=298 RH=80% EDMS=2.3x109molec cm-2s-1 (Davis et al.,1999)

  9. Total Concentrations

  10. Aerosol Composition in BL • Sulfate poor, sodium rich • Only solid is Na2SO4 • HCl can exist as gas • Most nitrate in the aerosol

  11. Aerosol Composition in BuL • Sulfate poor, • sodium rich • No solid • Nitrate in aerosol

  12. Aerosol Composition in FT tA/tS=2 tA/tS=1.25

  13. Aerosol Composition in FT

  14. pH and MSA gas MSA  MS- + H+

  15. Summary • The marine atmosphere becomes more acidic with increase in altitude. • The results suggest that MSA can be released to gas phase in pronounced amount in the dry and acidic FT. • Ammonia does not significantly affect the aerosol/gas partitioning in BL and BuL. However, the aerosol component is sensitive to ammonia in FT.

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