Long-term trends of chemical characteristics and sources of fine particle in Foshan City, Pearl River Delta: 2008-2014

Foshan is a major international ceramic center and the most polluted city in the Pearl River Delta (PRD). Here we present the results of the first long-term PM_2.5 (particles <2.5 μm) sampling and chemical characterization study of the city. A total of 2774 samples were collected at six sites from 2008 to 2014, and analyzed for water soluble species, elements and carbonaceous species. The major constituents of PM_2.5 were sulfate, OC (Organic Carbon), nitrate, ammonium and EC (Elemental Carbon), which accounted for 50%-88% of PM_2.5. PM_2.5 and the most abundant chemical species decreased from 2008 to 2011, but rebounded in 2012-2013. After 2008, the chemical composition of PM_2.5 changed dramatically due to the implementation of pollution control measures. From 2008 to 2011, SO₄^2- and NO₃^- were the two largest components; subsequently, however, OC was the largest component. The respective contributions of SO₄^2-, NO₃^- and OC to the sum of water soluble species and carbonaceous species were 30.5%, 22.9% and 19.9% in 2008; and 20.2%, 16.5% and 30.2% in 2014. Distinct differences in nitrate and sulfate, and in mass ratio [NO₃^-]/[SO₄^2-] imply that mobile sources tended to more important in Foshan during 2012-2014. The results indicate that pollution control measures implemented during 2008-2014 had a large effect on anthropogenic elements (Pb, As, Cd, Zn and Cu) and water soluble species, but little influence on crustal elements (V, Mn, Ti, Ba and Fe) and carbonaceous species. The PMF method was used for source apportionment of PM_2.5. Industry (including the ceramic industry and coal combustion), vehicles and dust were the three most important sources and comprised 39.2%, 20.0% and 18.4% of PM_2.5 in 2008, respectively. However, secondary aerosols, vehicles and industry were the three most important sources and comprised 29.5%, 22.4% and 20.4% of PM_2.5 in 2014, respectively. During the seven year study interval, the contributions of primary sources (industry and dust) decreased significantly, but secondary sources increased dramatically. Industry, dust and vehicles contributed 36.6 μg m^-3, 13.9 μg m^-3, and 9.2 μg m^-3 to the reduction of PM_2.5, respectively.