Effects Of Air Pollutants And Meteorological Conditions On Visibility

Haze, a phenomenon considered as the average daily visibility less than 5 km, which not only may lead to the serious urban visual impairment but also may cause an adverse health effect, and even change the global climate. Recent periods witnessed a serious urban visual impairment and haze occurrence in Changsha. Therefore, it is of significance to study the correlations of visibility with meteorological parameters and air pollutants, as well as the dominating pollution source which results in the significant visibility decline and more and more haze occurrences in Changsha.Firstly, this study not only investigated the correlations of urban visibility with the meteorological parameters and air pollutants and obtained the probable factors which lead to the visual degradation in Changsha, but also further revealed the crucial factors promoting to the haze formation by the analysis of the components of PM10 samples. In addition, based on the identification and apportionment of the major sources to PM10 pollution, this study found the dominating pollution source which results in the significantly decreased visibility during the hazy episodes in Changsha. At last, it also traced some original areas for this dominating source to Changsha. The major research methods of this study were:firstly, PM10 samples were collected in the suburban area of Changsha from November 2007 to October 2008, and then the 16 components (Na,Mg,Al,Si,P,S,Cl,K,Ca,Ti,Fe,Mn,Ni,Cu,Zn,Pb) of PM10 were obtained by Wavelength Dispersive X-ray Fluorescence (WD-XRF). Furthermore, the principal component analysis (PCA) method was adopted to identify and apportion the major pollution sources to PM10 in the suburban area of Changsha, while this study also used absolute principal component analysis (APCA) method to calculate the variation of the relative contribution for each different pollution source between hazy day (HD) and non-hazy day (NHD). At last, this study traced the potential original areas where contributed to the crucial pollution source by five-day backward air trajectories arriving Changsha with the largest contributions of dominating source.This study indicated that:(1) In the recent five years, the average visibility of Changsha was 4.45 km, while the averaged annual number of hazy day was 245 which accounted for 67% each year; (2) The urban visibility in Changsha was negatively correlated with SO2, NO2, PM10 pressure and relative humidity, while positively associated with temperature and wind speed; (3) Based on the PCR model, reducing the concentration of SO2 is the most efficient way to improve the urban visual range and reduce the frequency of haze formation; (4) Secondary aerosols and biomass combustion were the major factors contributing to the haze formation in Changsha, while secondary aerosols was the predominating source resulting in the visual impairment during the hazy episodes in Changsha. (5) There were three original tracks which contributing to the relatively large contribution of secondary aerosols in Changsha:Western and northern areas-from western Russia and then transported through Inner Mongolia, and at last arrived at Changsha); East areas-from the industrial cities (Jiangsu and Zhejiang provinces) to Changsha; Yellow Sea-from Yellow Sea area (sea salt) to Changsha.