中亚热带背景区重庆四面山大气气态总汞含量变化特征

以重庆市四面山森林自然保护区作为中亚热带背景区的典型代表,利用高时间分辨率自动测汞仪(Tekran 2537X)于2012-03~2013-02对该区域大气气态总汞(TGM)进行了连续1年的野外观测.结果表明,四面山地区气态总汞的年平均含量为(2.88±1.54)ng·m~(-3),高于北半球大气汞含量的背景值,低于国内大部分背景区监测点,表明以四面山为代表的中亚热带背景区大气汞从区域尺度而言尚属正常范围,但从全球大尺度比较,大气背景汞浓度已经有了一定程度升高.TGM浓度按季节表现为:冬季(3.68±2.43)ng·m~(-3)夏季(3.29±0.79)ng·m~(-3)春季(2.44±0.69)ng·m~(-3)秋季(2.13±0.97)ng·m~(-3),冬季TGM浓度变化波动较大.TGM日变化特征为春季夜间TGM浓度较高,秋、夏、冬三季白天TGM浓度较高,TGM浓度日变化与温度和光照强度有显著的正相关关系.从风向和后向轨迹模型分析的结果来看,重庆本地燃煤排放等是该地区气态总汞的主要来源,此外印度季风等造成的大气汞的长距离迁移也可能是该区域大气汞含量升高的原因.

Variation Characteristics of Total Gaseous Mercury at Simian Mountain Background Station in Mid-subtropical Region

Total gaseous mercury (TGM) was continuously monitored at the Simian Mountain Forest Nature Reserve in Chongqing, a representative of the mid-subtropical region, using high-resolution automatic atmospheric mercury vapor analyzer (Tekran 2537X) from March 2012 to February 2013. The results showed that the average concentration of TGM during the monitoring was (2.88±1.54) ng·m^-3, which was much higher than the background TGM on north hemisphere but lower than those at most of the other monitoring sites in China. These results suggested that the TGM level in Simian Mountain was still in the normal range on regional scale, but had an increasing tendency globally. The TGM level exhibited a distinct seasonal variation, following the order of winter (3.68±2.43) ng·m^-3>summer (3.29±0.79) ng·m^-3>spring (2.44±0.69) ng·m^-3>autumn (2.13±0.97) ng·m^-3, and the TGM concentration varied to a greater extent in winter. The diurnal variation of TGM concentration characterized as being higher at the nighttime in spring, while higher during the daytime in other seasons. The concentration variation of TGM had a positive correlation to temperature and light intensity. The result of backward trajectory analysis using HYSPLIT showed that the main source of the TGM in Simian Mountain was the local coal combustion, and long distance transportation by the Indian monsoon might also play a role in the increasing TGM level.