Chemical composition of PM2.5 during winter in Tianjin, China

PM2.5 samples for 24 h were collected during winter in Tianjin, China. The ambient mass concentration and chemical composition of the PM2.s were determined. Ionic species were analyzed by ion chromatography, while carbonaceous species were determined with the IMPROVE thermal optical reflectance (TOR)method, and inorganic elements were measured by inductively coupled plasma-atomic emission spectrometer. The daily PM2.s mass concentrations ranged from 48.2 to 319.2 μg/m3 with an arithmetic average of 144.6 μg/m3. The elevated PM2.5 in winter was mostly attributed to combustion sources such as vehicle exhaust, heating, cooking and industrial emissions, low wind speeds and high relative humidity (RH), which were favorable for pollutant accumulation and formation of secondary pollutants. By chemical mass balance, it was estimated that about 89.1％ of the PM2.s mass concentrations were explained by carbonaceous species, secondary particles, crustal matters, sea salt and trace elements. Organic material was the largest contributor, accounting for about 32.7％ of the total PM2.5 mass concentrations. SO42-,NO3-, Cl- and NH4+ were four major ions, accounting for 16.6％, 11.5％, 4.7％ and 6.0％, respectively, of the total mass of PM2.s.