Spatiotemporal distribution and long-range transport of atmospheric speciated mercury at three remote islands in Taiwan Strait and South China Sea

Abstract

This study investigated the spatiotemporal distribution and long-range transport of atmospheric speciated mercury at three remote islands in the Taiwan Strait and the South China Sea. The field measured speciated mercury in the atmosphere was then correlated with criteria air pollutants and meteorological parameters. Air mass trajectory simulation and global fire map were further used to explore potential source regions. Field measurement results showed that the yearly average concentration of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate mercury (PHg) in the target seas were 2.09±0.61 ng/m3, 20.93±7.81 pg/m3, and 150±70 pg/m3, respectively. The highest GEM, GOM, and PHg concentrations were always observed at the Penghu Islands in all seasons. Total gaseous mercury (TGM = GEM+GOM) was the dominant mercury species in the atmosphere, apportioned as 92.46– 96.17% TGM and 3.83– 8.70% PHg, respectively. The seasonal variation of GEM and PHg concentrations were ordered as: spring>winter>fall>summer, while GOM showed different seasonal trends. The lowest concentration of total atmospheric mercury (TAM) was observed in summer since clean air masses were blown mainly from the Pacific Ocean and the Philippines Islands. Air masses came mainly from Central China, North China, and Japan/Korea with the TAM concentrations of 2.90 ± 0.63, 2.68 ± 0.65, and 2.16 ± 0.45 ng/m3, and the frequencies of 19.3%, 18.3%, and 14.3%, respectively. Atmospheric speciated mercury positively correlated to O3, PM2.5, SO2, and NOx, implying that they were consistently emitted from anthropogenic sources in the upwind polluted regions. Overall, the concentrations of atmospheric speciated mercury measured at the three remote islands in the Taiwan Strait and the South China Sea were commonly higher than those in the United States and European countries, but lower than those in Asian countries, with the exception of Japan.