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

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/m3for 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.