Identifying regions that can constrain anthropogenic Hg emissions uncertainties through modelling

Abstract. Anthropogenic mercury (Hg) emissions are a major contributor to global Hg pollution. However, limitations in emission inventories and modeling approaches impede accurate quantification of Hg emissions and Hg ecosystem inputs, complicating the evaluation of mitigation policies. This study investigates how uncertainties in anthropogenic emissions, compared to chemistry and meteorology modeling uncertainties, affect model performance in model-observation comparisons, and explores strategies to evaluate emission uncertainties. We performed modeling experiments that incorporated four global anthropogenic emission inventories, which differ in Hg emissions by up to 630 Mg in Asia, 259 Mg in South America, and 252 Mg in Africa. Additionally, we employed two different chemical schemes and two meteorological datasets. Inventory differences were the primary driver of significant differences across modeled total gaseous mercury (TGM) concentrations in the Northern Hemisphere, resulting in ranges of up to 0.47 ng m⁻³ in China and 0.32 ng m⁻³ in India. These differences influenced Root Mean Square Error scores in TGM model–observation comparisons, ranging from 0.03 to 0.19 in Asia, 0.12 to 0.25 in the Arctic, and 0.02 to 0.14 in the USA in an annual mean. A signal-to-noise ratio (SNR) analysis identified regions such as the eastern U.S., Greenland, and Arctic Russia as valuable for constraining anthropogenic emissions. The existing limited Southern Hemisphere network offers limited constraints on emissions but provides possible insights into Hg chemistry. These findings highlight the need for an expanded monitoring network and more refined emission inventories to reduce uncertainties and improve the accuracy of global Hg policy evaluation.