Identification of potential sources of elevated PM_2.5-Hg using mercury isotopes during haze events

Atmospheric mercury (Hg) pollution has become a serious problem in megacities. In this study, we applied Hg isotopes together with backward-trajectory receptor models to investigate the potential sources and transport of elevated PM_2.5-Hg during two haze events in autumn (Oct. and Nov. in 2014) and winter (Jan. in 2015). Results showed that the sources and transport patterns of PM_2.5-Hg during haze are complex for different seasons. In autumn, the dominant sources were local and/or regional anthropogenic emissions from northern China, whereas the long-range transport contribution of biomass burning originated from northeastern China in 2014 and eastern China in 2015. Notably, the biomass burning from northeastern China served as an important contribution to elevated PM_2.5-Hg in winter. Our data set also suggested that the Δ²⁰⁰Hg_PBM values may be due to heterogeneous photoreactions on the particles emitted by coal burning, smelting, and cement production, along with photooxidation from the upper troposphere, and could be used as a potential indicator of particle-bound mercury sources owing to its contribution to the exhibited variability. Hg isotopes, together with meteorological models, could be employed to trace the sources of particle-bound Hg in the atmosphere. This study provides a new way to explore the potential sources of atmospheric particulate mercury and its vectors during haze evolution.