A full-scale analysis of chemical characteristics of PM2.5 and PM10 during haze and non-haze episodes in Cixi city, China

Abstract

With the objectives to understand the chemical characteristics of particulate matters in haze episodes, PM2.5 and PM10 samples were simultaneously collected for six days in each season from August 2013 to March 2014 in Cixi, China. The daily average concentrations of PM2.5 and PM10 in Cixi were 117 and 151μg/m3, respectively, which were higher than those in metropolises of China. The long-range air mass transport from northern China largely affected the particle levels in haze days in Cixi, while the air mass transport from the Pacific Ocean and the East China Sea diluted local pollutants in non-haze days. High enrichment factors of Cu, Sn, Zn, Pb and Se, ranging from 100 to 10,000, were found in PM2.5, revealing their predominant anthropogenic sources in Cixi, for instance industry emissions and vehicle exhaust. Similar emission sources of water-soluble inorganic ions at urban and suburban were observed, which indicated that the variations of their levels in haze and non-haze days were more regionally related than to locally. The NO3−/SO42− ratios, from 1.27 to 1.88 in haze days and lower than those in non-haze days, revealed that industry emissions might be more important than vehicle exhaust for the haze pollution. Compared with those in non-haze days, the mean concentrations of elements, water-soluble inorganic ions and carbonaceous species in PM2.5 and PM10 as well as PM2.5/PM2.5-10 mass ratios significantly increased in haze days, which indicated that haze was greatly beneficial to the accumulation of air pollutants, especially in fine particles.