https://www.selleckchem.com/products/corn-oil.html 8 μm), the aerosols in the accumulation mode were more hygroscopic and aerosols in the Aitken mode were less hygroscopic, with coarse mode aerosols being the least hygroscopic. During the polluted period, the particulate size notably increased, and the mass fraction of NO3- and SO42- in the accumulation mode aerosols was significantly higher than during the clean period. Accordingly, the hygroscopicity of accumulation mode aerosols was strongly enhanced during the polluted period[gκ(RH)=1.3-1.4] and aerosols in the 0.18-3.1 μm size range all had a strong hygroscopicity. On polluted days, the synergistic effect of the increase in particle size, water-soluble ions, and aerosol hygroscopicity results in the considerable deterioration of visibility.From November 16 to 28 2018, water-soluble ions in particulate matter and some trace gases in Nanjing City were observed using the online gas composition and aerosol monitoring system MARGA ADI 2080. Combined with meteorological elements and sounding data, the distribution characteristics and day-night differences of pollutants and water-soluble ions during haze, fog, clear, and precipitation processes were analyzed. The results show that the average concentration of PM2.5 varied from 26.9μg·m-3 (precipitation) to 96.4μg·m-3 (haze) while total water-soluble ions varied between 23.7μg·m-3 (precipitation) and 89.7μg·m-3 (haze). The ranked order of ion concentrations was NO3- > NH4+ > SO42- > Cl- > K+ > Ca2+ > Na+ > Mg2+ during haze and fog events, and NO3- > SO42- > NH4+ > Cl- > Ca2+ > K+ > Na+ > Mg2+ during clear weather and precipitation period. The diurnal distributions of water-soluble ions were quite different under the four conditions, although SO42-, NO3-, and NH4+(SNA) were ranked haze > fog > clear > precipitation for both day and night periods. According to the PMF source analysis, secondary sources were the main factors affecting haze; secondary sources, sea salt, an