||The Taiwan Strait is a densely populated and industrially developed area, where a large number of mercury is emitted to its atmosphere. Asian dust storms, biomass burning, and northeastern Monsoons frequently occurred in the spring and winter. It could lead to a large number of atmospheric mercury and anthropogenic air pollutants across the Taiwan Strait from long-range transportation, which could cause poor ambient air quality of the Taiwan Strait.|
This study aimed to measure the speciation and concentration of atmospheric mercury, and further investigated their tempospatial distribution. The concentrations of total gaseous mercury (TGM) and particulate mercury (Hgp) were measured at six sampling sites surrounding the Taiwan Strait. A standard method for sampling and analyzing mercury in air (NIEA Method A304.10C) announced by the National Institute of Environmental Analysis (NIEA), mostly adopted from USEPA Method IO-5, was applied for the measurement of TGM and Hgp. This study also sampled TGM and Hgp in a sampling vessel (R/V Ocean Researcher III) navigated in the Taiwan Strait, and developed a KCl-coated annular denuder to sample reactive gaseous mercury (RGM) in the east side of the Taiwan Strait, and further investigated the tempospatial distribution of atmospheric mercury concentration. In addition, this study applied a NOAA-HYSPLIT Model and a Global Fire Map to figure out the transportation routes of polluted air mass by a backward trajectory, a fire spot map, and the correlation analysis of mercury concentration with meteorological parameters and criteria air pollutants.
The results showed that the concentration of TGM and Hgp measured at six sites surrounding the Taiwan Strait were 4.56±0.35 ng/m3 and 0.17±0.02 ng/m3 with the range of 3.22-5.84 ng/m3 and 0.06-0.25 ng/m3, respectively, and were ordered as : spring >winter > fall > summer. Moreover, the highest TGM and Hgp concentration was observed at the Xiamen Xiang-Ann site. Atmospheric mercury apportioned as 95.70~ 98.34% TGM and 1.66~4.35% Hgp. The emission of Hgp came mainly from metropolitan areas and only small part of them emitted from industrial areas. Total atmospheric mercury apportioned as 1.34~1.79% RGM. RGM concentration were ordered as : Kaohsiung Gushan > Taichung Sha-Lu > New Taipei City Sandiaojiao. The results indicated that the RGM concentration at Kaohsiung Gushan was higher than other sites. While measured in the sampling vessel, the atmospheric mercury in the Taiwan Strait was mainly transported from the North China and mainland´s coastal areas.
Results obtained from backward trajectory simulation and meteorological data showed that, in summer, the air masses transported toward the Taiwan Strait was mainly come from the South China Sea. The concentration of TGM and Hgp in summer appeared to be relatively lower than those in other seasons. However, the atmospheric mercury levels surrounding the Taiwan Strait increased in fall, winter, and spring, while the air masses were transported from the Northeast Asia by northeastern Monsoons.
During the Dongsha Islands sampling periods, the prevailing winds were blown from either the east or the northeast in spring. The backward trajectory simulation results showed that the air masses toward the Dongsha Islands were mostly transported from the East China Sea through the Bashi Channel between the Taiwan and the Luzon Islands. Very few combustion or pollution discharge activities in these regions, resulting in much lower TGM concentration at the Dongsha Islands than that surrounding the Taiwan Strait. Compared to other cities in the world, the concentration of atmospheric mercury surrounding the Taiwan Strait was generally lower than the cities of mainland China, but higher than Japan, Korea, European, and American cities.