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Taking Beijing-Tianjin-Hebei (BTH) with severe atmospheric mercury (Hg) and PM 2.5 pollution as a typical region, this study clarified the characteristics and transboundary transport of atmospheric Particulate Bound Mercury (PBM 2.5) affected by the East Asian monsoon. Five sampling sites were conducted in rural, suburban, urban, industrial, and coastal areas of BTH from northwest to southeast along the East Asian monsoon direction. PBM 2.5 showed increasing concentrations from northwest to southeast and negative δ202Hg values, indicating significant contributions from anthropogenic sources. However, the mean Δ199Hg values of PBM 2.5 at the five sites were significantly positive, probably triggered by the photoreduction of Hg(II) during long-range transport driven by the East Asian monsoon. Apart from local anthropogenic emissions as the primary sources, the transboundary transport of PBM 2.5 , driven by west and northwest air masses originating in Central Asia and Russia, contributed significantly to the PBM 2.5 pollution of BTH. Moreover, these air masses reaching BTH would carry elevated PBM 2.5 concentrations further transported to the ocean by the East Asian monsoon. In contrast, the southeast air masses transported from the ocean by the East Asian monsoon in summer diluted inland PBM 2.5 pollution. This study provides insight into the atmospheric Hg circulation affected by the East Asian monsoon. [Display omitted] • Anthropogenic sources affected the PBM 2.5 in BTH, identified by Hg and N isotopes. • East Asian monsoon-driven transport contributed significantly to atmospheric PBM 2.5. • Photoreduction of Hg2+ during long-range transport led to elevated Δ199Hg of PBM 2.5. • The northwest monsoon from the inland intensified atmospheric PBM 2.5 pollution. • The southeast monsoon from the ocean alleviated atmospheric PBM 2.5 pollution. [ABSTRACT FROM AUTHOR]