Chemical Compositions and Liquid Water Content of Size-Resolved Aerosol in Beijing

For aerosol related studies, the size distribution and hygroscopicity of chemical components are very important information. In order to characterize the distributions of chemical compositions and the water absorption ability for ambient aerosols of Beijing, a MOUDI-120 sampler was used to collected size-resolved samples in three seasons. All the samples were analyzed in the laboratory for water-soluble inorganic ions and carbon fractions. The size-resolved aerosol liquid water content (ALWC) of the sampled particles was modeled by the ISORROPIA II. The distributions of the chemical compositions, the ALWC, and the charge balance conditions were all discussed for three different pollution levels. During the sampling, the aerosols in stages 6–10 (< 1.0 μm) were under relatively dry conditions due to the significant pressure drops. Three modes (condensation mode, droplet mode, and coarse mode) could be identified from the distributions of the main chemical components and the ALWC. For the droplet mode, the ammonium was not enough to balance NO3– and SO42– during the heavily polluted period. The influence of relative humidity on ALWC is greater than that of the chemical compositions.