In this study, the vertical characteristics of PM2.5 pollution were comparative analyzed between the heavy polluted and unpolluted air in January 2014 at Tianjin. Tianjin is one of the most polluted cities in China. A medium-volume sampler was used to collect samples of PM2.5 for consecutive 15 days; collecting heights of four tiers were 10, 40, 120 and 220 m in a meteorological tower. The study found that, 1). Overall, the concentration of PM2.5​​ was almost 6 times higher in the heavy polluted air than that in the clean air; the concentration of PM2.5 decreased with increasing height, 220 m with lowest concentration, and 40 m with highest concentration. Generally, the concentration of PM2.5 between 220m and 40m had a large difference in heavy pollution weather, and it had a relatively small difference in the clean weather. 2). As the height increases, the percentage of SO42- and total carbon declined, and the percentage of NO3- and the rate of NO3- / SO42- increased. The percentage of Al, Si, Ca and secondary ions (SO42- and NO3-) were higher in the pollution weather than that in the clean weather, while the percentage of carbon was relatively lower. 3). The different chemical components of PM2.5 explained the different sources, as well as the different atmospheric chemical processes for different weather types and different heights. By the characters of the chemical component, it can be speculated that crustal dust, vehicle exhaust, coal dust, construction dust and secondary aerosols were the possible source categories. The proportion of secondary sources increased as the height increases. Meanwhile, the contribution of secondary aerosols became greater in the heavy polluted air, which showed that the impact of secondary reactions was significant.

Comparative study of PM2.5 vertical characteristics between heavy pollution weather and clean weather in Tianjin, China

249th National Meeting (2015)

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