Real-Time Observation on Water-Soluble Ions of PM2.5 in Beijing under the Influences of Different Air Masses in Summer

Abstract

To further understand the variations of water-soluble ions in PM2.5 in Beijing, the authors observed their concentrations continuously and in high temporal resolution by the system for rapid collection of fine particles and ion chromatography (RCFP-IC) during 12–18 July 2010. These results combined with those of earlier backward trajectory research are used analyzed to determine the causes of concentration changes in water-soluble ions under the influences of two kinds of air masses in summer. The results indicate that concentrations of NO3−, SO42−, and NH4+ were influenced strongly by the continental air mass than by the marine air mass. Cl− and Na+ were not changed significantly. Because the sources of K+, Mg2+, and Ca2+ are mainly concentrated on land, their concentration levels were slightly higher under the control of continental air mass than that of the marine air mass. Variations of NO2− during the observation differed from those of other ions; its concentration was significantly higher under the influence of marine air mass. Moreover, the authors obtain the diurnal variations of eight water-soluble inorganic ions including NH4+, K+, Mg2+, Ca2+, Cl−, NO2−, NO3−, and SO42−. Diurnal variations of NH4+, NO3−, and Cl− showed single peak, which appeared before noon, while SO42− showed two peaks that appeared during rush hours. Those of Mg2+, Ca2+, and K+ showed single peak that appeared in the afternoon. That of NO2− showed with a peak appearing at sunrise and a valley appearing at sunset.