Emerging investigator series: investigation of mercury emission sources using Hg isotopic compositions of atmospheric mercury at the Cape Hedo Atmosphere and Aerosol Monitoring Station (CHAAMS), Japan

Abstract

This study conducted mercury (Hg) isotopic analysis, which has been expected as a new indicator for understanding the behavior of atmospheric Hg. The dominant atmospheric Hg species, namely gaseous elemental mercury (GEM, Hg⁰), were collected at the Cape Hedo Atmosphere and Aerosol Monitoring Station (CHAAMS) in Okinawa, Japan, for evaluating possible source(s) and transformation process(es) of Hg. The Hg isotopic compositions of GEM samples showed that the mass-dependent fractionation (MDF) of δ²⁰²Hg and the mass-independent fractionation (MIF) of Δ¹⁹⁹Hg ranged from −2.15‰ to 0.79‰ and from −0.32‰ to 0.00‰, respectively. The results were classified into two groups: (1) negative δ²⁰²Hg and near-zero Δ¹⁹⁹Hg in summer and (2) near-zero δ²⁰²Hg and negative Δ¹⁹⁹Hg in the other season. According to the NOAA Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, the dominant air masses traveled from East Asia during winter and South and East Asia during summer. However, the air masses also traveled from mainland Japan and rotated around Okinawa before reaching CHAAMS. In contrast, clear positive correlations between δ²⁰²Hg values and CO and PM_2.5 concentrations were observed during summer. A small peak of O_x concentration was observed at three atmospheric monitoring stations, namely Nago, Naha, and Miyako Island during summer. Since Miyako Island is located ∼370 km southwest of CHAAMS, the main emission source of GEM transported to CHAAMS was not from mainland Okinawa but traveled from the southwest during summer.