Correlation slopes of GEM / CO, GEM / CO2, and GEM / CH4 and estimated mercury emissions in China, South Asia, the Indochinese Peninsula, and Central Asia derived from observations in northwestern and southwestern China

摘要

Correlation analyses between atmospheric mercury (Hg) andother trace gases are useful for identification of sources and constrainingregional Hg emissions. Emissions of Hg in Asia contribute significantly tothe global budget of atmospheric Hg. However, due to the lack of reliabledata on the source strength, large uncertainties remain in the emissioninventories of Hg in Asia. In the present study, we calculated thecorrelation slopes of GEM / CO, GEM / CO, and GEM / CH for mainlandChina, South Asia, the Indochinese Peninsula, and Central Asia using theground-based observations at three remote sites in northwestern and southwesternChina, and applied these values to estimate GEM emissions in the four sourceregions. The geometric mean GEM / CO correlation slopes for mainland China,South Asia, the Indochinese Peninsula, and Central Asia were 7.3 ± 4.3,7.8 ± 6.4, 7.8 ± 5.0, and 13.4 ± 9.5 pg m ppb,respectively, and values in the same source regions were 33.3 ± 30.4,27.4 ± 31.0, 23.5 ± 15.3, and 20.5 ± 10.0 pg m ppb forthe GEM / CH correlation slopes, respectively. The geometric means ofGEM / CO correlation slopes for mainland China, South Asia, and CentralAsia were 240 ± 119, 278 ± 164, 315 ± 289 pg m ppm,respectively. These values were the first reported correlation slopes ofGEM / CO, GEM / CO, and GEM / CH in four important source regions ofAsia, not including the GEM / CO ratios in mainland China. The correlation slopes ofGEM / CO, GEM / CO, and GEM / CH in Asia were relatively higher thanthose observed in Europe, North America, and South Africa, which mayhighlight GEM emissions from non-ferrous smelting, large-scale and artisanalmercury and gold production, natural sources, and historically depositedmercury (re-emission) in Asia. Using the observed GEM / CO and GEM / COslopes, and the recently reported emission inventories of CO and CO,the annual GEM emissions in mainland China, South Asia, the IndochinesePeninsula, and Central Asia were estimated to be in the ranges of1071–1187, 340–470, 125, and 54–90 t, respectively. The estimatedquantity of GEM emissions from the GEM / CH correlation slopes issignificantly larger, which may be due to the larger uncertainties inCH emissions in Asia as well as insufficient observations ofGEM / CH correlation slopes, therefore leading to an overestimate of GEMemissions. Our estimates of GEM emissions in the four Asian regions weresignificantly higher (3–4 times) than the anthropogenic GEM emissionsreported in recent studies. This discrepancy could come from a combinationof reasons including underestimates of anthropogenic and natural GEMemissions; large uncertainties related to CO, CO, and CHemission inventories; and inherent limitations of the correlation slopemethod.