[Chemical Species of PM2.5 in the Urban Area of Beijing].

From August 2012 to July 2013, 220 groups of PM2.5 samples were continuously collected at four locations in the urban area of Beijing (Shijingshan, Chegongzhuang, Dongsi, and Tongzhou), and the primary chemical species of PM2.5 were analysed by the chemical mass balance method. It was found that the mass of PM2.5 obtained from chemical mass balance method agreed well with the value from gravimetric measurement, with a good correlation of 0. 95 in spring, autumn, and winter. However, the correlation seasonally changed in summer, with a relatively lower correlation coefficient of 0. 77. The concentrations of OM, EC, SO(4)2-, NO3-, NH4+, Cl-, crustal matter, and trace species were 31. 4, 3. 8, 19. 9, 21. 6, 14. 4, 4. 0, 15. 4, and 2. 9 µg.m-3, which accounted for 25. 1%, 3. 0% , 15. 9%, 17. 2%, 11. 5%, 3. 2%, 12. 3%, and 2. 3% of PM2, , respectively. Besides crustal matter, concentrations of the primary chemical species in PM2.5 from the west to the east gradually increased. The most serious PM pollution occurred between 11 and 14 February 2013, during which concentrations of OM, SO2-, NO3-, NH4+ were 1. 9, 5. 0, 3.2 and 4. 2 times as high as the annual average. SO(4)2- was recognized as the most important species for the pollution in the process. OM was the largest component of urban PM2.5 during both heating and non-heating periods. Comparing to non-heating period, the concentrations of OM, NH4+, NO3-, and SO(4)2- all increased during the heating period, except for the component of crust and EC. The biggest difference between the two periods was the component of Cl- (4. 4 fold), which can be attributed to the burning of coal. For unknown components, the main component was moisture, which accounted for about 6.0% in urban PM2.5. The highest moisture appeared in summer (6. 5%), followed by spring and winter, and the least appeared in fall (3. 7% ).