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Long-term trend of visibility and its characterizations in the Pearl River Delta (PRD) region, China

摘要:

This paper suggests that the rapid increase in urbanization and human activities has important impacts on visibility in the Pearl River Delta (PRD) region. A long-term trend of visibility in Guangzhou (one of the largest cities in PRD) shows that between 1954 and 2006, there is a rapid change in visibility. Between 1954 and 1972, low visibility has the smallest occurrence (less than a few days per year). Between 1972 and 1980, the visibility condition is within a transition period, and the occurrence of low visibility increases rapidly. Between 1980 and 2006, the occurrence of low visibility remains very high (150 days year 1), suggesting that the city of Guangzhou is often under low-visibility conditions since the 1980s. In order to understand the causes of the low visibility in Guangzhou, we analyze physical and chemical characterizations of a low-visibility event occurring between 15 and 29 November 2005. The analysis suggests that high concentration of aerosol particles is a major cause for the low visibility. The threshold aerosol concentration that is corresponding to the low visibility (< 10 km) is about 120 mu g m(-1). Further analysis indicates that the relationship between aerosol concentrations and visibility appears in a non-linearity correlation. When aerosol concentrations are very high (above 120 mu g m(-3)), the change in visibility is not sensitive to aerosol concentration. By contrast, when aerosol concentrations are < 120 mu g m(-3), the change in visibility is very sensitive to aerosol concentrations. This study also shows that absorbing aerosol particles (such as element carbon (EC) play important roles in the reduction of visibility. In most cases, the extremely low visibility (<2 km) is often resulted from high EC concentrations (above 15 mu g m(-3)). In averaged condition, small scattering aerosol particles (< 1 mu m in radius) have the largest contribution to the reduction of visibility (about 70%). By contrast, large scattering

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作者: Deng, XJ [1] ; Tie, XX [2] ; Wu, D [3] ; Zhou, XJ [4] ; Bi, XY [5] ; Tan, HB [6] ; Li, F ; Hang, CL
作者单位: Natl Ctr Atmospher Res, Boulder, CO 80303 USA [1] Peking Univ, Sch Phys, Dept Atmospher Sci, Beijing 100871, Peoples R China [2] China Meteorol Adm, Inst Trop &amp [3] Marine Meteorol, Key Open Lab Trop Monsoon, Guangzhou, Peoples R China [4] CMA, China Acad Meteorol Sci, Beijing, Peoples R China [5] Shanghai Meteorol Bur, Shanghai, Peoples R China [6]
DOI: 10.1016/S0895-7061(02)03004-2
发布时间: 2013-01-01
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