Dominant Contributions of Secondary Aerosols and Vehicle Emissions to Water-Soluble Inorganic Ions of PM2.5 in an Urban Site in the Metropolitan Hangzhou, China

Abstract

Water soluble inorganic ions (WSIIs) are important components in PM2.5 and could strongly affect the acidity and hygroscopicity of PM2.5. In order to achieve the seasonal characteristics and determine the potential sources of WSIIs in PM2.5 in Hangzhou, online systems were used to measure hourly mass concentrations of WSIIs (SO42−, NO3−, NH4+, Cl−, Na+, K+, Ca2+ and Mg2+) as well as PM2.5, NO2 and SO2 at an urban site for one month each season (May, August, October, December) in 2017. Results showed that the hourly mass concentrations of PM2.5 during the whole campaign varied from 1 to 292 μg·m−3 with the mean of 56.03 μg·m−3. The mean mass concentration of WSIIs was 26.49 ± 20.78 μg·m−3, which contributed 48.28% to averaged PM2.5 mass. SNA (SO42−, NO3− and NH4+) were the most abundant ions in PM2.5 and on average, they comprised 41.57% of PM2.5 mass. PM2.5, NO2, SO2 and WSIIs showed higher mass concentrations in December, possibly due to higher energy consumption emissions, unfavorable meteorological factors (e.g., lower wind speed and temperature) and regional transport. Results from PCA models showed that secondary aerosols and vehicle emissions were the dominant sources of WSIIs in the observations. Our findings highlight the importance of stronger controls on precursor (e.g., SO2 and NO2) emissions in Hangzhou, and show that industrial areas should be controlled at local and regional scales in the future.