Characteristics of the water-soluble components of aerosol particles in Hefei, China

Abstract

Size-classified daily aerosol mass concentrations and concentrations of water-soluble inorganic ions were measured in Hefei, China, in four representative months between September 2012 and August 2013. An annual average mass concentration of 169.09μg/m3 for total suspended particulate (TSP) was measured using an Andersen Mark-II cascade impactor. The seasonal average mass concentration was highest in winter (234.73μg/m3) and lowest in summer (91.71μg/m3). Water-soluble ions accounted for 59.49%, 32.90%, 48.62% and 37.08% of the aerosol mass concentration in winter, spring, summer, and fall, respectively, which indicated that ionic species were the primary constituents of the atmospheric aerosols. The four most abundant ions were NO3−, SO42−, Ca2+ and NH4+. With the exception of Ca2+, the mass concentrations of water-soluble ions were in an intermediate range compared with the levels for other Chinese cities. Sulfate, nitrate, and ammonium were the dominant fine-particle species, which were bimodally distributed in spring, summer and fall; however, the size distribution became unimodal in winter, with a peak at 1.1–2.1μm. The Ca2+ peak occurred at approximately 4.7–5.8μm in all seasons. The cation to anion ratio was close to 1.4, which suggested that the aerosol particles were alkalescent in Hefei. The average NO3−/SO42− mass ratio was 1.10 in Hefei, which indicated that mobile source emissions were predominant. Significant positive correlation coefficients between the concentrations of NH4+ and SO42−, NH4+ and NO3−, SO42− and NO3−, and Mg2+ and Ca2+ were also indicated, suggesting that aerosol particles may be present as (NH4)2SO4, NH4HSO4, and NH4NO3.