Seasonal Variation and Source Apportionment of Water-Soluble Ions in PM2.5 in Quanzhou City

Abstract

In this study, the seasonal characteristics of water-soluble ions (WSIs) present in fine particulate matter (PM2.5) in Quanzhou City were investigated. PM2.5 samples were collected at five different sites in the city from March 2014 to January 2015 and the concentrations of Na+, NH4+, K+, Ca2+, Mg2+, F-, Cl-, NO3-, and SO42- were determined by ion-exchange chromatography. In order to identify the sources of these WSIs, the positive matrix factorization (PMF) analysis was applied. The seasonal variations in total WSI concentrations were found to decrease in the order of spring > winter > summer > autumn. The ions SO42-, NO3-, and NH4+ were the major WSIs found in PM2.5, accounting for 90.3%±3.3%, 68.8%±11.7%, 78.9%±7.1%, and 74.0%±18.4% of the total amount of ions found in spring, summer, autumn, and winter, respectively. These results suggested that the level of secondary ions was relatively high in the spring season. The anion-to-cation ratio in each of the four seasons was less than one, which indicated that PM2.5 in Quanzhou City was slightly alkaline. Furthermore, NH4+ ions in PM2.5 mostly existed in the form of (NH4)2SO4, NH4HSO4, and NH4NO3 during spring and winter, while they were primarily found as NH4HSO4 and NH4NO3 in the summer and autumn seasons. PMF analysis revealed that marine salt, secondary sources, fugitive dust from construction, municipal incineration, and biomass burning were the main potential sources of the ionic components of PM2.5.