Variations in submicron aerosol liquid water content and the contribution of chemical components during heavy aerosol pollution episodes in winter in Beijing.

Abstract

The aerosol liquid water content (ALWC) of submicron particles (PM1) was calculated in this work by three methods based on the aerosol physical and chemical properties measurement campaigns in winter in Beijing, including (a) the PM1 volume difference between the ambient and dry states by applying the particle number size distribution and particle hygroscopicity measurement; (b) the thermodynamic equilibrium model (ISORROPIA II) based on the chemical composition; and (c) the κ-Köhler theory of chemical composition with a volume mixing scheme. The three methods agreed well with reasonable uncertainties. The ALWC showed an exponential trend depending on the relative humidity (RH), and an abundant ALWC was also favored by the high PM1 mass loading. The contribution of different chemical component to the ALWC was evaluated by the κ-Köhler method, which revealed that during the measurement, the inorganics and organics could contribute to ~80% and ~20%, respectively, under ambient RH conditions, with the largest contributor of ammonium nitrate. When the RH was above 85%, the mass concentration of ALWC was comparable to, or even larger than, that of the dry PM1.