||Taiwan is located at the eastern edge of the Eurasian Continent. Mercury accompaning with other air pollutants could be long-range transported to Japan, Korea, Hawaii, and even arrived the western coast of American Continent. Moreover, it could also cause potential impacts on Taiwan. Local and long-range transport emissions arising from different types of mercury may change its characteristics. Additionally, air passes through the cities emitted mercury-containing pollutants during the transportation process, resulting in the increase of atmospheric mercury concentration.|
This study aims to investigate the seasonal variation and source identification of atmospheric speciated mercury at the Penghu Islands. Both continuous monitoring (Tekran, Model 2537B) and manual sampling (USEPA IO-5) of atmospheric mercury were simultaneously conducted to measure the concentration of total gaseous mercury (TGM), particulate mercury (PHg), and gaseous oxidized mercury (GOM) in the atmosphere. Field sampling and analysis of atmospheric speciated mercury were conducted in winter (January), spring (April), summer (July), and fall (November) of 2013 at three sampling sites during the daytime (8:00-20:00) and nighttime (20:00-08:00) sampling periods, respectively, in order to understand the spatiotemporal distribution of atmospheric mercury at the Peughu Islands. The present study referred previous literatures about gaseous oxidized mercury (GOM) sampling and analytical methods, and combined with the existing published standard methods to conduct the sampling and analysis of GOM. This study further applied NOAA-HYSPLIT Model backward trajectory simulation plots and global fire maps to estimate the potential emission sources and the transportation routs of atmospheric air masses and further correlated with the meteorological parameters and criteria air pollutants.
The concentrations of atmospheric mercury as TGM at the Penghu Islands showed a significant seasonal variation and ordered as spring> winter> fall> summer. The concentration of TGM ranged from 2.78 to 6.07 ng/m3 with an average of 4.60 ± 1.38 ng/m3, and the highest concentration occurred at A3 site. The variation of TGM concentration between A1 and A2 sites was in steady state, while the TGM concentration variation at A3 site was undulating between the hours of 18:00 to 23:00, presumably due to the emissions from fishing boats. The seasonal variation of GOM and PHg concentrations showed that GOM concentrations were in order as summer> spring> winter> fall, while PHg concentrations were in order as spring> winter> summer> fall. Diurnal variation of GOM and PHg concentrations showed that the average GOM concentrations at daytime and nighttime were 0.108 ± 0.094 ng/m3 and 0.054 ± 0.037 ng/m3, respectively, with the concentration range of 0.041 ~ 0.244 ng/m3 and 0.013 ~ 0.103 ng/m3, respectively, and the highest concentration was observed at A2 site. The average PHg concentrations at daytime and nighttime were 0.329 ± 0.167 ng/m3 and 0.210 ± 0.124 ng/m3, respectively, with the concentration range of 0.190 ~ 0.565 ng/m3 and 0.071 ~ 0.319 ng/m3, respectively, and the highest concentration was recorded at A1 site. The partition of PHg ranged from 4.8% to 19.4% of total atmospheric mercury (TAM). In addition, the distribution of gas-solid phase mercury might be attributed from anthropogenic and mobile sources, and followed by industrial emissions.
The NOAA-HYSPLIT backward trajectory simulation plots and global fire maps showed that, during the spring sampling period, contaminated air masses flowed through the coastal areas of northern China with high current transmission reflux which affected the east and the south and then transferred contaminants to the Penghu Islands. During the summer sampling period, contaminated air masses were blown mainly from South China Sea and the Philippines which had less combustion source emissions and thus made atmospheric mercury concentrations much lower than in other seasons. During the fall and winter sampling periods, the coastal exuberant industrial emissions from mainland and air mass laden mercury contaminants from the Korea Peninsula were transported by the prevailing monsoon long-range transport of mercury containing pollutants to the Penghu Islands.