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 (PM_2.5) 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 PM_2.5 samples displayed a significant spatial difference in δ²⁰²Hg. For the CX site, the negative δ²⁰²Hg 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 Hg, whereas the observed positive δ²⁰²Hg at the DMS site was likely associated with regional emissions and extended atmospheric processes during transport. The Δ¹⁹⁹Hg values in PM_2.5 from the CX and DMS sites were comparably positive. The unity slope of Δ¹⁹⁹Hg versus Δ²⁰¹Hg over all data suggests that the odd mass independent fractionation (MIF) of Hg was primarily induced by the photoreduction of Hg²⁺ in aerosols. The positive Δ²⁰⁰Hg values with a minor spatial difference were probably associated with the photooxidation of Hg0, which is generally enhanced in the coastal environment. Total Hg in offshore surface seawater was characterized by negative δ²⁰²Hg and near-zero Δ¹⁹⁹Hg and Δ²⁰⁰Hg values, which are indistinguishable from Hg isotopes of source materials. Overall, the PM_2.5 collected from industrial areas had comparable δ²⁰²Hg values but more positive Δ¹⁹⁹Hg and Δ²⁰⁰Hg 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.