Characterization of chemical compositions in size-segregated atmospheric particles during severe haze episodes in three mega-cities of China

Abstract

To investigate the characterization of chemical compositions in size-segregated particles during severe haze pollution episodes in different regions of China, a campaign was conducted in Tianjin, Hangzhou and Chengdu. Size-segregated particles were collected with eight-stage Anderson cascade impactor in these cities in winter respectively. Ten major compositions of particles including (Na+, NH4+, K+, Mg2+, Ca2+, Cl−, NO3−, SO42−, OC and EC) were analyzed. A similar bimodal distribution of particles was found between northern and southern cities peaked at 0.7–2.1 and 9.0–10.0μm. OC, EC, SO42−, NO3−, Cl− and NH4+ were the major chemical compositions of fine-mode particles, whereas OC, EC, SO42−, NO3− and Ca2+ were the major compositions of coarse-mode particles. In the three cities, Cl−, SO42−, NO3−, NH4+ and K+ of all compositions were unimodal distributions peaked at 0.7–2.1μm. Different sources to particles in the three cities were inferred based on the size distribution characteristics of chemical compositions. For Tianjin, the influence of sea salt was greater to Hangzhou and Chengdu based on the concentrations and distributions of Na+ and the Cl−. Fine-mode Cl− and SO42− were highest in Tianjin, meaning the greater contribution of coal burning to particles during severe pollution. For Hangzhou, the NO3− concentration was higher than Tianjin and Chengdu. Contribution of nitrate to PM was higher than that of sulfate. For Chengdu, carbonaceous species contributed mostly to fine particles. However, sulfate and nitrate contributed mostly to fine particles in Tianjin and Hangzhou. The contributions of EC and Ca2+ to coarse-mode particles was much higher than that in other cities, implying the greater influence of soil particles, construction dust or falling dust to PM in Chengdu. In addition, there were greater emission source of NH4+ in Chengdu. Northwest, west and southeast were the major transport pathways of air masses for Tianjin, Hangzhou and Chengdu.