Supplementary material to "Mercury isotopic compositions in fine particles and offshore surface seawater in a coastal area of East China: Implication for Hg sources and atmospheric transformations"

Isotopic compositions of Mercury (Hg) in atmospheric particles (HgPM) are probably the mixed results of emission sources and atmospheric processes. Here, we present Hg isotopic compositions in daily fine particles (PM2.5) collected from an industrial site (Chunxiao - CX) and a nearby mountain site (Daimeishan - DMS) in a coastal area of East China, and in surface seawater close to the industrial area, to reveal the influence of anthropogenic emission sources and atmospheric transformations on Hg isotopes. The PM2.5 samples displayed a significant spatial difference in delta Hg-202. For the CX site, the negative delta Hg-202 values are similar to those of source materials, and the HgPM contents were well correlated with chemical tracers, indicating the dominant contributions of local industrial activities to HgPM2.5, whereas the observed positive delta Hg-202 at the DMS site was likely associated with regional emissions and extended atmospheric processes during transport. The Delta Hg-199 values in PM2.5 from the CX and DMS sites were comparably positive. The unity slope of Delta Hg-199 versus Delta Hg-201 over all data suggests that the odd mass independent fractionation (MIF) of HgPM2.5 was primarily induced by the photoreduction of Hg2+ in aerosols. The positive Delta Hg-200 values with a minor spatial difference were probably associated with the photooxidation of Hg-0, which is generally enhanced in the coastal environment. Total Hg in offshore surface seawater was characterized by negative delta Hg-202 and near-zero Delta Hg-199 and Delta Hg-200 values, which are indistinguishable from Hg isotopes of source materials. Overall, the PM2.5 collected from industrial areas had comparable delta Hg-202 values but more positive Delta Hg-199 and Delta Hg-200 as compared to surface seawater. The results indicate that atmospheric transformations would induce the significant fractionation of Hg isotopes and obscure the Hg isotopic signatures of anthropogenic emissions.