East, Southeast, and South Asia are the major anthropogenic mercury (Hg) emission source regions, contributing close to 50% of the global anthropogenic Hg emissions. While atmospheric and rainwater Hg monitoring activities have been steady in East Asia (China, Korea, Japan and Taiwan), such activities are limited in Southeast and South Asia due to the lack of monitoring capacity. A wet Hg deposition monitoring network, consisting of 11 sampling sites in Taiwan and a remote island site in subtropical Northwest Pacific Ocean, was established to collect weekly rainwater samples for total Hg analysis since 2009. The purpose of this network is to develop information on spatial and seasonal trends in wet Hg deposition and to evaluate the contribution of regional/long-range transport. Range of annual volume-weighted mean (VWM) Hg concentrations of this network is close to the range of values reported by NADP/MDN. However, annual wet Hg deposition fluxes in Taiwan are usually higher than in North America, mainly due to the higher annual rainfall in Taiwan.

Since 2012, the Environmental Protection Administration Taiwan (EPAT), National Central University (NCU), U.S. Environmental Protection Agency (USEPA) and National Atmospheric Deposition Program (NADP) worked together to assist Southeast and South Asian countries in capacity building of atmospheric Hg monitoring and to systematically monitor wet deposition and atmospheric concentrations of Hg in a network of stations throughout the Asia-Pacific region, resulting in the establishment of the Asia-Pacific Mercury Monitoring Network (APMMN). Currently, eight network sites measure Hg in precipitation following standardized procedures adapted from NADP. The network also has a common regional analytical laboratory at NCU, and quality assurance procedures which ensure the network makes scientifically valid and consistent measurements. Results from our ongoing analytical and field quality assurance measurements show minimal contamination in the network and accurate analytical analyses. We are continuing to monitor a potential concentration and precipitation volume bias between various types of wet deposition sampler.