| The north china plain is a region with megacities, powerful industry and huge populations. Beijing locates in the center of this plain. In the past few decades, rapidly industrializing North China has contributed massive quantities of anthropogenic pollutions into the troposphere because of the inadequate pollution controls fostered by weak regulations. And aerosols over the highly polluted area have a significant impact on the regional climate, visibility and human health.In order to better understand the impact of atmospheric particulate matters from different sources on the air quality in Beijing for efficiently making air pollution control, over 500 filter samples were sampled monthly for each season during a continuous 1-year campaign at a suitable site, one subway station in north Beijing for SEM-EDX analysis. The composition and morphology of all aerosol particles were classified into five groups:mineral (including over 4 types of different mineral particles), carbonaceous (6 types), fly ash, sulfur (S)-rich (internally mixed with organic matter and soot), K-rich. The result showed the morphology of mineral particle was mainly irregular, and its source could be introduced to local/exotic soil and constructional dust. There are different shapes of carbonaceous particles such as flocculent, schistose, balls, strips and net under the SEM which also means different source. Air quality index perfectly fits the change of number and concentration among different days. Calcium-sulfate particles significantly increased in haze days of summer and winter compared with other particles, while Ca-Mg particles decreased a lot. The formation of A2D particle required strong sunlight. A2B and A2C particles are the major formality of A2 type, A2C focus on the earlier and later stage of haze days. The abundance of B1 soot particles was higher than any other particles at clean days in all seasons, while the concentration of B2 balls increased a lot in winter due to coal burning. At haze days in summer, C1 WSOC in PM1-2.5 fraction increased a lot, the number of C2-C4 in PM0.5-1 increased as much as 1000% in autumn and winter compared with that at clean days along with a relevant high concentrations of B1 and B2 particles. To all the special particles, high humidity and relative high concentration of NOx contributed a lot to the formation of WSOC, plenty of S-rich particles were detected during haze days in winter, which also means its existence on the surface of a great number of carbonaceous particles as the core and medium of second reaction in atmosphere.The abundance of carbonaceous particles in the evolution process of haze days in the spring changed opposite the air quality index. At the beginning and end of this process, and the process just before and after reaching the peak concentration, abundance of carbonaceous particles were relative high, while at the days which were defined as the top polluted days it fell down to a smaller value. However in the summer, it changed along with the air quality index. The types of A2 particles were always different in the different stage of haze process, and the proportion of mineral particles was once as much as 60%. The number of A2D from exotic source increased a bit in the autumn, and biomass burning such as the fire and smoke caused by the burning of straws left in the field after harvest, released a lot of EC like B1 particles and OC like C2 and C3 particles. And vehicle emission was no longer the main source of carbonaceous particles. The proportion of carbonaceous particles in total numbers of all particles rose to more than 80%, just before and after the process of haze days, mineral particles, especially calcium-sulfate particles increased a bit. The coal burning would release some C2 particles without any C3 particles. And the number of B2 particles reached its top value in all seasons. Organic carbon increased and decreased with the process of haze days. Dominate pollution particles in different seasons are also different. |
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