Shifting Hotspots of Mercury Emissions from Global Coal-Fired Power Units during 1990–2020 and the Role of Overseas Investments

Coal-fired power plants (CFPPs) are the second-largest source of anthropogenic mercury (Hg) emissions worldwide. However, unit-based, long-term Hg emission inventories have been largely limited to China, leaving global CFPP emissions poorly characterized. In addition, Hg emissions associated with overseas coal-fired power plant (OCP) investments remain insufficiently understood. Here, we developed a unit-based Hg emission inventory for 12,474 CFPPs worldwide, including 754 OCPs, covering the period 1990–2020, to elucidate the spatiotemporal evolution of Hg emissions and their driving factors. Our results show that global Hg emissions from CFPPs increased steadily from 232.3 Mg in 1990 to a peak of 310.0 Mg in 2012, followed by a decline to 275.4 Mg in 2020. Over this period, emissions decreased markedly in the Global North but increased in the Global South, leading to a pronounced southward shift in emission hotspots. Although total Hg emissions from OCPs remained relatively stable, their spatial distribution also exhibited a clear southward migration. Notably, Hg emissions from OCPs in the 7.5°N–32.5°N latitudinal band increased by a factor of 327, from 0.02 Mg in 1990 to 5.7 Mg in 2020. Our findings suggest that emission hotspots will progressively shift from currently dominant regions such as China and India toward more southerly regions, highlighting the urgent need for the deployment of advanced mitigation technologies in these areas.