Chemical Characteristics Of Fine Particulates During Air Pollution Episodes In Autumn Of Shanghai, China

In order to understand the chemical characteristics of particulates in Shanghai, continuous measurement was conducted in urban area of Shanghai from May,2010 to April,2011. Mass concentraction of particulates, chemical composition of PM2.5, the concentraction of gas pollutions such as SO2, NO2 and O3 and meteorological dates were obtained. In this study, particulate matter characteristics all year round in Shanghai were investigated. Besides, the mass concentration and chemical characteristics of PM2.5 during different pollution episodes, including haze and sand storm episodes, were analyzied. The results show that:1. Through the one year monitoring of particulate in Shanghai, the annual mean mass concentrations of PM10, PM2.5 and PM10 were 91.1μg·m-3,50.2μg·m-3 and 34.3μg·m-3, respectively, and the ratio of PM2.5 to PM10 was 55.1%, the fine particle contributed more to PM10.Maximum particulate concentrations appeared in November and December, the mean concentrations were over 140μg·m-3, while the minimum appeared in August and December, and the mean concentrations were blow 65μg·m-3. Particulate concentration was negatively correlated with relative humidity, wind speed and atmosphere temperature, and different wind direction also can affect the mass concentration of particulate.2. The minimum visibility of Shanghai appeared in February, June, November and December, and monthly mean visibility was 16.1 km,15.6 km,18.5 km and 18.7 km, respectively. The maximum visibility appeared in August and December, and the monthly mean visibility was 31.6 km and 34.6 km. The visibility was negatively correlated with relative humidity and the mass concentration of PM2.5.3. The maximum daily mass concentrations of PM10 and PM2.5 were 216～293μg·m-3 and 130～204μg·m-3, respectively, during the haze episode, and the ratio of PM2.5 to PM10 was over 65%. Additionally, the total water soluble inorganic irons (TWSⅡ) accounted for more than 50% of the mass concentration of PM2.5, and the carbonaceous particle (OC and EC) contributed 25～30% to the PM2.5 mass concentration. Secondary water soluble irons (SO42-, NO3-, NH4-) contributed 83.3～87.5% to TWSⅡ, and the ratio of OC/EC was around 5, suggesting the large contribution from secondary formation to PM2.5, during the haze episode.4. The maximum daily mass concentrations of PM10 and PM2.5 were 539μg·m-3 and 133μg·m-3 during the sand storm episode, and the ratio of PM2.5 to PM10 was 24.6%. Different from the haze episode, the coarse particle contributed more to PM10 during the sand storm episode, with TWSⅡ, OC and EC accounting only for 27.2%,13.4%,2.0%, and secondary water soluble irons contributed 55.7% to the TWSⅡ. Meanwhile, larger proportion of crust ions (Ca2+, Mg2+) in PM2.5 was found during the sand storm episode than that during the haze episode.5. High concentrations of secondary ions in haze days were usually resulting from the strong oxidation of sulfur and nitrogen. During the haze episode, the oxidation ratios of sulfur and nitrogen reached 0.24±0.10 and 0.15±0.06, suggesting the strong transformation of NO2 and SO2 to NO3- and SO42-.