Characterization Of Sub-micron Aerosol And Its Change Processes In BIV (Beijing And Its Vicinity) Region

The physical and chemical feature of sub-micron aerosol is the basis to understand metropolitan low visibility, haze and CCN formation in the regional scale. Monitoring for chemical components and the size distribution of these sub-micro particles can help us to study on the secondary aerosol formation and evolution process. It is also the necessary condition for insighting into the reason of haze in city.BIV (Beijing and its vicinity) is the represent for north of China. It is suffered from the serious air pollution. In order to solve the issue of air pollution, it is an urgent task to know the formation and evolution of sub-micron aerosol, the reason of haze, and make the controlling measures. Three observation stations were set up for the long-term measurements of the chemical components, size distribution and number concentration of sub-micro aerosol. Based on the measured data, the total condition of these stations, the sources of different organic aerosol, formation process of secondary sub-micron, the relationship between aged aerosol and haze were further discussed in this study. All of these results can supply the valuable parameters for both climate change model and particle nuclear and growth model.From June 2007 to June 2009, measurements of physical and chemical characteristics for sub-micro aerosol have been taken in Beijing. Two campaigns in December 2006 and May 2007were explored in Gucheng station. One campaign in July 2009 was made in Wuqing station. It shows that the concentration of sub-micron aerosol in BIV is higher than that in the cities in developed countries significantly. The average concentration of sub-micron aerosol in Beijing is 60μg/m3, which contains 27μg/m3 organics, 13μg/m3 Sulfate,11μg/m3 nitrate, 7μg/m3 ammonium and 1.5μg/m3 chloride. For Gucheng, the average concentration in winter and spring is 79μg/m3 and 24.4μg/m3 respectively. For Wuqing, the average concentration of sub-micron aerosol is 20μg/m3, which is lower than that in Beijing. During all of these measurements, it is concluded that organics is the dominant components in the sub-micron aerosol.The diurnal cycle of sub-micron and the chemical components shows high concentration from evening to early morning, and low concentration in daytime. In Beijing, additional peak in noon was found for organics, but wasn't found in Gucheng and Wuqing, The accumulation mode particles in sub-micron aerosol is higher than others in different season. In winter, there are more aitken mode particles than other season. The size distribution for organics is wider than inorganic species. The sub-micron mass concentration and the size distribution can also be influenced by meteorological factors. Both Precipitant and high wind speed can reduce the mass concentration effectively, but the wind direction impact little on the mass concentration.It is classified into three kind of organic aerosol according to the sources, which is hydrocarbon organic aerosol (HOA), less oxidized organic aerosol (OOA II) and more oxidized organic aerosol (OOA I). It is shown that most of HOA come from local combustion emission and the oxidized organic aerosol come from regional pollutants transportation and gas-particle transformation. Sulfate and Nitrate correlate well with OOA I in winter, but they correlate well with but OOA II in other seasons.During measurements, regional new particle formation events (NPFs) were observed frequently. Especially in spring, more NPF events were observed than other seasons, and less NPF events were observed in winter. The NPF events occurred not only after cold wind blow, precipitant but also in high air pollution background. The chemical components in sub-micron aerosol play different roles in this kind of events. Organics and sulfate are the necessary components in the particle formation and growth, but nitrate doesn't involve into the formation and early growth process. Generally speaking, during the earlier growth of particles, the growth rate of organics is higher than that of sulfate, but during the later growth of particles, sulfate grows faster than organics.The higher temperature, humidity and stable meteorological situation are very benefit for particles hygroscopic growth, condensation and coagulation, and the aged aerosol were formed accordingly. With the classical hygroscopic growth of nitrate and sulfate, organics also experience the condensation growth, and the secondary soluble organics may play some roles in this growth. The size distribution of aged aerosol is always dominant by accumulation mode particles with peak size at 500-600 nm. The high concentration and the accumulation mode features of aged aerosol are the main reason for haze.The acidity of aerosol varied in Beijing varies in different seasons and months. Except August and September in 2008, which are neutral aerosol, all the others measurements show that the aerosol in Beijing are acid. Especially in winter, it is strong acid than other season. In fall, the aerosol acidity is weaker.