冬季降雪过程对城市大气气态汞污染的影响

2009年降雪和非降雪期间对北京西北城区的气态总汞浓度进行了连续采样，比较了降雪期间、非降雪期间的气态总汞浓度日变化过程；降雪期间气态总汞浓度的降低和恢复过程。结果表明，降雪和非降雪期间大气气态总汞浓度的日均值有显著差异，降雪期间气态总汞的平均浓度为5．64ng·m^-3，非降雪期间的平均浓度为7．43ng·m^-3，前者约为后者的70％。降雪后约7h气态总汞浓度恢复到降雪前水平。研究中分析了气象因素（气压、风速、阵风速度、气温和相对湿度）对于气态总汞浓度的影响，结果表明：降雪期间主要受到风速（r=-0．527）和阵风速度（r=-0．574）的影响；非降雪期间主要受到风速（r=-0．691），阵风速度（r=-0．726）和相对湿度（r=0．692）的影响，并且相对湿度的影响与风速的影响相近。降雪和非降雪期间气态总汞的日变化有所差异：非降雪期间气态总汞浓度在午夜和清晨较高，日变化趋势与相对湿度一致；降雪期间气态总汞的日变化没有明显规律。

Influence of snowing event on gaseous mercury concentration in urban atmosphere

An intensive field monitoring campaign was conducted for measurement of total gaseous mercury (TGM) in Beijing urban area during the snow period, 2009. Results show the mean concentration of TGM within 96 hours after the first snowing event is about 70% of the concentrations during dry days. The impact of meteorological factors on TGM concentration, including air pressure, wind speed, gust speed, temperature and relatively humidity, were analyzed Results indicate that the meteorological influences on TGM were mainly caused by wind speed (r= -0.527), gust wind speed (r= -0.574) during the snow period; while during dry days, influences were caused by wind speed (r= -0.691), gust wind speed(r= -0.726) and relatively humidity(r= 0.692). During dry days, the TGM in the mid-night and early morning was much higher, and the daily variation showed a similar trend with the relative hu-midity; while during snow days, no clear variation pattern was observed.