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Calculating equilibrium droplet sizes under different RHs and its applications

Calculating equilibrium droplet sizes under different RHs and its applications. Wei-Chun Hsieh 2005/4/27. Motivation. Ratio of scattering coefficient s s (RH)/ s s,d Hygroscopic growth factor What factors make difference of these two measurements? guess chemical components.

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Calculating equilibrium droplet sizes under different RHs and its applications

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  1. Calculating equilibrium droplet sizes under different RHs and its applications Wei-Chun Hsieh2005/4/27

  2. Motivation • Ratio of scattering coefficient ss(RH)/ss,d • Hygroscopic growth factor • What factors make difference of these two measurements? • guess • chemical components

  3. Initial dry condition Soluble volume: Vs Insoluble volume: Vn Total dry volume: V=Vs+Vn q = Vs’/V Total aerosol volume: Veq insoluble soluble Initial dry aerosol is composed of soluble and insoluble portions: Derivation of swelling ratio of particle based on simple equations m: molality Ms: molecular weight of solute Mw: molecular weight of water nw: numbers of moles of water in the drop ns: numbers of moles of solute in the drop ρs: density of the dry solute ρs’: apparent density of the solute ρw: density of the water rs: dry radius of the particle req: equilibrium drop radius Let Then ns can be expressed

  4.  independent of q

  5. Soluble matter: (NH4)2SO4 v.s. NaCl Problems come from?

  6. Numerical calculation of equilibrium droplet size: Method • Köhler equation: saturation vapor pressure over the drop surface • Given • Environmental temperature Ts=293K • Environmental RH • Particle size rs=1mm (molar mass of solutes can be calculated) • get equilibrium water mass at ambient RH=S for an aerosol which is composed of soluble and insoluble parts • Let Q=insoluble volume ratio of the particle • Bisection method to get converged solution rs Soluble: ammonia sulfate (NH4)2SO4 Insoluble: Black carbon

  7. Size swelling ratiooriginal particle size 1mm

  8. Soluble:(NH4)2SO4

  9. Rs=1mm

  10. Area swelling ratio f(RH) with low reference RH=30%

  11. Rs=0.01mm

  12. Parameterization of swelling ratio as function of RH, insoluble volume ratio

  13. Calculation scattering coefficient, how? • Assuming initial dry aerosol size distribution • Appling parameterization equation to get the equilibrium size of particle under different RH, insoluble volume ratio • Using radiation scheme codes to obtain the scattering coefficient • Qscat: Mie scattering efficiency

  14. In addition, gases emitted from biomass fires in Porto Velho may have condensed onto particles transported from Maraba, thereby supplying a more hydrophobic surface coating and changing the hygroscopic properties of the aerosol.

  15. Aerosol size distribution

  16. Discussion • Parameterization of size swelling ratio • Advantages: fast, sample • Disadvantage: accuracy • This study can be applied to obtain the first-order insoluble volume of the aerosol • If this works… • Save chemical measurements • Mixture scenario • Chemical component is not just one

  17. Thank you Questions?

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