Distribution Characteristics and Source Analysis of Water-soluble Ions in Particulate Matter Under Different Weather Processes in Nanjing

Abstract

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, and combustion sources were the main pollution sources to foggy conditions; and the removal effect of precipitation on coal-fired sources and secondary sources was more notable than during clear conditions.