Chemical characterization, the transport pathways and potential sources of PM2.5 in Shanghai: Seasonal variations.

The 24-h PM 2.5 samples were collected at the site of East China University of Science and Technology (ECUST) in Shanghai from 2011 to 2012, representing winter, spring, summer and autumn, respectively. And PM 2.5 and its chemical components including organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), humic-like substance carbon (HULIS-C) and water-soluble ions were analyzed. The results suggested that the average PM 2.5 concentrations were (70.35 ± 43.75) μg/m 3 , (69.76 ± 38.67) μg/m 3 , (51.26 ± 28.25) μg/m 3 and (82.37 ± 48.70) μg/m 3 in winter, spring, summer and autumn, respectively. Secondary inorganic ions (sulfate, nitrate and ammonium) were the dominant pollutants of PM 2.5 in the four seasons. Total carbon (TC) was an important component explaining above 15% of PM 2.5 . OC/EC ratios were all above 2 ranging from 4.31 to 6.35; particularly in winter it reached the highest 6.35 which demonstrated that secondary organic carbon (SOC) should be a significant composition of PM 2.5 . The SOC calculated based on the OC/EC ratio method had stronger correlation with WSOC in summer and autumn (summer: R 2 = 0.73 and autumn: R 2 = 0.75). The HULIS-C and SOC most significantly correlated in autumn (R 2 = 0.83). The data showed that PM 2.5 atmospheric aerosols were more acidic in autumn and the concentrations of PM 2.5 and its chemical components were much higher. Factor analysis (FA), cluster analysis of air mass back trajectories, potential source contribution function (PSCF) model and concentration weighted trajectory (CWT) model were used to investigate the transport pathways and identify potential source areas of PM 2.5 in different seasons. FA identified various sources of PM 2.5 : secondary aerosol reactions, the aged sea salts and road dusts. The results of cluster analysis, PSCF model and CWT model demonstrated that the local sources in the Yangtze River Delta Region (YRDR) made significant contributions to PM 2.5 . During winter and autumn long-time transport from the Circum-Bohai-Sea Region (CBSR) and northwestern China including the Inner Mongol had adverse effects. [ABSTRACT FROM AUTHOR]