Characteristics and Source Analysis of Water-Soluble Ions in PM2.5 in Zhengzhou

Abstract

In order to explore the pollution characteristics of water-soluble ions in PM2.5 in Zhengzhou, high time resolution and continuous observation of water-soluble inorganic ions in PM2.5 was conducted from December 1, 2017, to November 30, 2018, in Zhengzhou. The results showed that during the observation period, the average concentration of total water-soluble ions in Zhengzhou was 42.7 μg·m-3. The order of mass concentration of each ion, from large to small, was as follows:NO3-(17.7 μg·m-3), SO42-(10.2 μg·m-3), NH4+(9.0 μg·m-3), Cl-(2.3 μg·m-3), K+(1.3 μg·m-3), Na+(1.3 μg·m-3), Ca2+(0.8 μg·m-3), and Mg2+(0.1 μg·m-3). The mass concentration of total water-soluble ions was the highest in winter, slightly higher in autumn than in spring, and lowest in summer. The diurnal variation in single peak distribution was observed across the whole year in spring, summer, and autumn, while there was no significant diurnal variation in winter. The mass concentration of secondary inorganic ions (SO42-, NO3-, and NH4+) accounted for 43.8% of PM2.5, mainly in the form of (NH4)2SO4 and NH4NO3. There was a large degree of secondary transformation throughout the observation period; relative humidity had a significant influence on the sulfur oxidation rate, and temperature had a significant influence on the nitrogen oxidation rate. During the observation period, there was a good correlation between secondary ions, and K+ showed a good correlation with Mg2+ and Cl-. The main source of the secondary ions was the secondary conversion of gaseous pollutants. Mg2+ and Ca2+ were derived from soil dust and construction dust. K+ was one of the main biomarkers of biomass combustion. Na+ was mainly derived from sea salt and soil dust, and Cl- was derived not only from sea salt but also biomass and fossil fuel combustion. The results of principal component analysis showed that the water-soluble ions in PM2.5 in Zhengzhou were mainly affected by secondary transformation, combustion sources, and dust emission from soil or building construction.