Water-soluble ionic composition of PM2.5–10 and PM2.5 aerosols in the lower troposphere of an industrial city Raipur, the eastern central India

Abstract

Size-segregated aerosol samples were collected at Raipur, India, during the period of October 2008 to September 2009, using eight-stage cascade impactor-type aerosol sampler at a flow rate of 28.3 l/min. The results give information about the mass concentrations, seasonal variations, and sources of water-soluble inorganic species viz. Na+, NH 4 + , K+, Mg2+, Ca2+, Cl-, NO 3 - , and SO 4 2- in both PM2.5–10 (coarse) and PM2.5 (fine) fractions. Annual mean of mass concentrations of PM2.5–10 and PM2.5 aerosols were monitored to be 200.7 ± 55.1 and 185.9 ± 66.9 μg/m3, respectively. The annual mean concentrations of the inorganic components were monitored to be 5.4 ± 2.4, 6.2 ± 4.7, 5.3 ± 1.8, 3.2 ± 0.46, 40.8 ± 7.9, 9.2 ± 3.8, 21.6 ± 5.5, and 17.9 ± 4.0 μg/m3 in PM2.5–10 aerosols and 4.1 ± 2.1, 13.4 ± 4.2, 7.7 ± 2.0, 1.7 ± 0.4, 18.7 ± 5.4, 9.7 ± 3.1, 13.4 ± 5.7, and 36.8 ± 10.0 μg/m3, respectively, in PM2.5 aerosols, for the above ions. The concentration of Na+, Mg2+, and Ca2+ were higher in spring and summer. The seasonal variation of secondary components NH 4 + , NO 3 - , and SO 4 2- were similar; that means high concentration in winter and low concentration in fall. The results obtained from factor analysis suggested the presence of three main components/sources in the coarse and fine modes namely regional pollution, airborne road dust, and traffic emissions, which contributed 94.0% and 83.2% of the total variance of the system respectively for the PM2.5–10 and PM2.5 aerosols data set.