摘要
Daily PM_（2.5）（particulate matter with an aerodynamic diameter of below 2.5 μm） mass concentrations were measured by gravimetric analysis in Chinese Research Academy of Environmental Sciences（CRAES）, in the northern part of the Beijing urban area, from December 2013 to April 2015. Two pairs of Teflon（T1/T2） and Quartz（Q1/Q2） samples were obtained, for a total number of 1352 valid filters. Results showed elevated pollution in Beijing,with an annual mean PM_（2.5）mass concentration of 102 μg/m^3. According to the calculated PM_（2.5）mass concentration, 50% of our sampling days were acceptable（PM_（2.5）〈 75 μg/m^3）, 30% had slight/medium pollution（75–150 μg/m^3）, and 7% had severe pollution（〉 250 μg/m^3）. Sampling interruption occurred frequently for the Teflon filter group（75%） in severe pollution periods,resulting in important data being missing. Further analysis showed that high PM_（2.5）combined with high relative humidity（RH） gave rise to the interruptions. The seasonal variation of PM_（2.5）was presented, with higher monthly average mass concentrations in winter（peak value in February, 422 μg/m^3）, and lower in summer（7 μg/m^3 in June）. From May to August, the typical summer period, least severe pollution events were observed, with high precipitation levels accelerating the process of wet deposition to remove PM_（2.5）. The case of February presented the most serious pollution, with monthly averaged PM_（2.5）of 181 μg/m^3 and 32% of days with severe pollution. The abundance of PM_（2.5）in winter could be related to increased coal consumption for heating needs.
Daily PM_（2.5）（particulate matter with an aerodynamic diameter of below 2.5 μm） mass concentrations were measured by gravimetric analysis in Chinese Research Academy of Environmental Sciences（CRAES）, in the northern part of the Beijing urban area, from December 2013 to April 2015. Two pairs of Teflon（T1/T2） and Quartz（Q1/Q2） samples were obtained, for a total number of 1352 valid filters. Results showed elevated pollution in Beijing,with an annual mean PM_（2.5）mass concentration of 102 μg/m^3. According to the calculated PM_（2.5）mass concentration, 50% of our sampling days were acceptable（PM_（2.5）〈 75 μg/m^3）, 30% had slight/medium pollution（75–150 μg/m^3）, and 7% had severe pollution（〉 250 μg/m^3）. Sampling interruption occurred frequently for the Teflon filter group（75%） in severe pollution periods,resulting in important data being missing. Further analysis showed that high PM_（2.5）combined with high relative humidity（RH） gave rise to the interruptions. The seasonal variation of PM_（2.5）was presented, with higher monthly average mass concentrations in winter（peak value in February, 422 μg/m^3）, and lower in summer（7 μg/m^3 in June）. From May to August, the typical summer period, least severe pollution events were observed, with high precipitation levels accelerating the process of wet deposition to remove PM_（2.5）. The case of February presented the most serious pollution, with monthly averaged PM_（2.5）of 181 μg/m^3 and 32% of days with severe pollution. The abundance of PM_（2.5）in winter could be related to increased coal consumption for heating needs.
基金
supported by the State Environmental Protection Commonweal Trade Scientific Research,Ministry of Environmental Protection of China (No.2013467010)
The financial support of this special fund for the public service sector and research support from the staff of Chinese Research Academy of Environmental Sciences (CRAES) (Z141100002714002)
