Modeling of Mercury Deposition in India: Evaluating Emission Inventories and Anthropogenic Impacts

Abstract

Mercury (Hg), a ubiquitous atmospheric trace metal posing serious health risks, originates from natural and anthropogenic sources. India, the world’s second-largest Hg emitter and a signatory to the Minamata Convention, is committed to reducing emissions. However, critical gaps exist in our understanding of the spatial and temporal distribution of Hg across the vast Indian subcontinent due to limited observational data. This study addresses this gap by employing the GEOS-Chem model with various emission inventories (UNEP2010, WHET, EDGAR, STREETS, UNEP2015) to simulate Hg variability across the Asian domain, with a specific focus on India from 2013 to 2017. Model performance was evaluated using ground-based GMOS observations and literature data. Emission inventory performance varied across stations. Hence, we employed ensemble results from all inventories. The maximum relative bias for TGM and GEM concentrations is about ± 20%, indicating simulations with sufficient accuracy. Hg wet deposition fluxes are highest over the Western Ghats and the Himalayan foothills due to higher rainfall. During the monsoon, the Hg wet deposition flux is about 65.4% of the annual wet deposition flux. Moreover, westerly winds cause higher wet deposition in summer over northern and eastern India. Hg Dry Deposition flux accounts for 72-74% of total deposition over India. Hg dry deposition fluxes are higher over eastern India, which correlates strongly with the leaf area index. Excluding Indian anthropogenic emissions from the model simulations resulted in a substantial decrease (21.9% and 33.5%) in wet and dry Hg deposition fluxes, highlighting the dominant role of human activities in Hg pollution in India.