| dc.description.abstract |
East Asia is the highest atmospheric mercury emission region in the world, various studies have shown that downwind area in East Asia has high atmospheric mercury concentration and deposition by using model simulations. Atmospheric wet deposition is the important source of mercury pollution to the ecosystem. However, there was lack of studies about mercury wet deposition in the downwind area in East Asia, especially long-term data analysis. Therefore, the mercury wet deposition weekly data from Taiwan EPA during 2010-2015 used at three stations in North Taiwan, include Taipei (urban), Pengjia islet (remote island) and Anbu (mountain) station, to discuss the temporal and spatial variation of the mercury wet deposition in Northern Taiwan.
VWM Hg concentration in Taipei, Pengjia islet and Anbu station were 10.60, 7.77 and 9.97 ng L-1 respectively, which were similar to other stations in Europe and North America. Mercury wet deposition flux were 25.12, 12.92 and 45.36 µg m-2 yr-1 in three stations respectively, North Taiwan is located in the subtropical region, which had higher rainfall compare with Europe and North America, also sample mercury deposition flux was positively correlated with sample rainfall amount. Therefore, mercury deposition flux was higher than Europe and North America, especially in Anbu station.
However, the seasonal variation of rainwater mercury concentration was not clear at Pengjia islet and Anbu station, while it was the highest in Summer at Taipei. In summer, the dominated wind is southwest monsoon in North Taiwan, which took clearer air mass to Taiwan, the source of mercury might relate to high convection rain is more frequently in summer, air mass may mix with a global pool of RGM in the free troposphere, which provides the source of the mercury.
Correlation analysis performed with Hg concentration of each sample and rainfall amount, results showed that the washout effect in Taipei and Anbu station was weak, there should have continuous source beside local emission. Different events were separated according to weather systems causing rain, we found that Hg VWM concentration was the highest in the type of afternoon thunderstorm at both three stations, which show there was high reactive gaseous mercury in the free troposphere and provide a continuous source to rainwater.
Both VWM concentration and wet deposition flux had obvious yearly variation, 2 times difference between the maximum and minimum value, it might relate to the large-scale climate system. Correlation analysis performed between South Oscillation Index and above two parameters. However, the length of data was too short to compare with long-term climate index, longer data was needed to get a conclusion. | en_US |