Measurements of size-resolved hygroscopicity in the California coastal zone

Abstract. Aircraft-based measurements of aerosol hygroscopicity, both in the form of size-resolved, diameter growth factors and in the dependence of particle light scattering on relative humidity, are presented for the marine boundary layer of the southern California coastal zone. The chemical composition of the aerosol is collated with the hygroscopicity data, both to examine the mechanism for the increase in aerosol hygroscopicity with altitude and as input for receptor type modeling. The data suggest an increase in aerosol hygroscopicity with altitude, possibly associated with oxidation of organic films. The receptor modeling suggests three distinct aerosol types/sources for this venue: marine, biomass burning and pollution. Model output is used in regression analyses to derive a prognostic mixing rule for the hygroscopicity of aerosol with these three sources. The mixing rule demonstrated substantial prognostic power for submicron hygroscopicity but essentially none for supermicron.