“…The East Asian region has been one of the largest emission source regions in the world (Streets et al, 2003;Ohara et al, 2007;Zhang et al, 2009). Since SO 2 emitted from anthropogenic sources and volcanic eruptions is oxidized in the atmosphere during long-range transport and forms SO 2− 4 , which causes acidification of soil, land, water, and vegetation, the issue of transboundary air pollution evokes significant scientific interest and political concern (Carmichael et al, 2002).…”