Historical (1850–2010) mercury stable isotope inventory from anthropogenic sources to the atmosphere

Mercury (Hg) stable isotopes provide a new tool to trace the biogeochemical cycle of Hg. An inventory of the isotopic composition of historical anthropogenic Hg emissions is important to understand sources and post-emission transformations of Hg. We build on existing global inventories of anthropogenic Hg emissions to the atmosphere to develop the first corresponding historical Hg isotope inventories for total Hg (THg) and three Hg species: gaseous elemental Hg (GEM), gaseous oxidized Hg (GOM) and particulate-bound Hg (PBM). We compile δ202Hg and Δ199Hg of major Hg emissions source materials. Where possible, δ202Hg and Δ199Hg values in emissions are corrected for the mass dependent Hg isotope fractionation during industrial processing. The framework and Hg isotope inventories can be updated and improved as new data become available. Simulated THg emissions from all sectors between 1850s and 2010s generally show an increasing trend (−1.1‰ to −0.7‰) for δ202Hg, and a stable trend (−0.02‰ to −0.04‰) for Δ199Hg. Δ200Hg are near-zero in source materials and therefore emissions. The δ202Hg trend generally reflects a shift of historically dominant Hg emissions from 19th century Hg mining and liquid Hg0 uses in Au/Ag refining to 20th century coal combustion and non-ferrous metal production. The historical δ202Hg and Δ199Hg curves of GEM closely follow those of THg. The δ202Hg curves of GOM and PBM show no trends. Δ199Hg values for both GOM and PBM decrease from the 1850s to 1950s by ∼0.1‰, and then gradually rebound towards the 2010s. Our updated δ202Hg values (−0.76 ± 0.11 ‰, 1SD, n=9) of bulk emissions from passively degassing volcanoes overlap with δ202Hg of present-day anthropogenic THg emissions.