| dc.description.abstract | Global anthropogenic emission inventories indicated that Asia is the region with the greatest proportion of anthropogenic mercury (Hg) emissions to the atmosphere, particularly in East and Southeast Asia. In addition, recent observation and modeling studies suggested that tropical forest areas may be hotspots of atmospheric Hg depositions. However, long-term studies on atmospheric Hg concentration and deposition in these regions are still quite limited. This work, for the first time, presents and analyzes the long-term observation of speciated atmospheric Hg, wet and dry deposition of atmospheric Hg at Lulin Atmospheric Background Station (LABS), a high mountain tropical forest site downwind of the East Asian continent. Nighttime (0–8 am) data of gaseous elemental Hg (GEM), which is more representative of regional influence, between April 2006 and December 2016 were used for trend analysis. Significant decreasing trends in GEM concentrations at LABS were observed, in agreement with the reductions in atmospheric Hg export from the East Asia continent that has been suggested by recent studies. Changes in the frequency distribution of air mass origins and transport paths may also contribute to the changes in GEM concentrations at LABS. Besides, the decreasing trends observed with air from the ocean indicated declining background GEM concentrations in Northern Hemisphere. Multi-year of dry and wet Hg depositions at LABS were studied. The dry/wet deposition ratio of 2.8 was observed, indicating that Hg deposition to forest landscape was governed by dry rather than wet deposition. Both dry and wet Hg depositions at LABS were higher than those reported from the temperate region, suggesting that tropical forest mountains in East and Southeast Asia could be hot spots of atmospheric Hg deposition. Rainfall amount and rainfall types were the important factors in determining the seasonal distribution of wet Hg deposition. On the other hand, the seasonal distribution of dry Hg deposition was controlled by atmospheric Hg concentrations, temperature, and wind speed. GEM was the major dry deposition contributor at LABS, suggesting the important role of vegetation activity in forest ecosystems due to the uptake of Hg(0) by foliage. One-year observation data of total gaseous mercury (TGM) isotopic compositions were used to investigate the drivers responsible for the variation of TGM isotopic compositions at LABS. The results indicated that the variability of δ202HgTGM was attributed to vegetation activity, whereas the seasonal variation of ∆199HgTGM was likely driven by the seasonal changes in air mass origins and transport paths. This study, therefore, provides observational evidence for the role of vegetation activity at LABS. A case study was conducted to explore the relationship between atmospheric Hg and aerosol optical parameters during the biomass burning (BB) long-range transport periods at LABS. Positive correlations were found with R2 ranging from 0.12 to 0.7, suggesting carbonaceous aerosols and Hg are not only simultaneously emitted from the same source but also could reside in a similar pool of BB aerosols. Additionally, the positive correlation between particulate bound Hg (PBM) and absorption Ångström exponent (AAE370-880) likely suggests that the Hg(II) may be preferably absorbed by organic aerosols. | en_US |