Dominant Contributions of Secondary Aerosols and Vehicle Emissions to Water-Soluble Inorganic Ions of PM_(2.5) in an Urban Site in the Metropolitan Hangzhou, China

Abstract

Water soluble inorganic ions (WSIIs) are important components in PM_(2.5) and could strongly affect the acidity and hygroscopicity of PM_(2.5). In order to achieve the seasonal characteristics and determine the potential sources of WSIIs in PM_(2.5) 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 PM_(2.5), 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 PM_(2.5) 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 PM_(2.5) and on average, they comprised 41.57% of PM2.5 mass. PM_(2.5), 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.

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