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Volcanic eruptions are important natural sources of gases and aerosols to the environment. However, their impact on the global cycle of trace elements, including mercury (Hg), remains poorly understood. On 9 April 2021, La Soufrière volcano (13.33°N, 61.18°W) erupted in the Caribbean Sea. Ozone Monitoring Instrument (OMI) measurements of sulfur dioxide (SO 2) tracked the transport of volcanic SO 2 in the troposphere over long distances from the source, including to the western North Pacific ∼10 day after eruption. A spike in gaseous and particle-bound mercury concentrations along with a peak in aerosol back-scattering coefficient at Lulin Atmospheric Background Station (LABS, 23.47°N, 120.87°E; 2862 m AMSL) coincided with the volcanic plume transport on 19 April. The slope of gaseous elemental mercury vs. carbon monoxide concentrations during the event was 0.027, which is distinctly higher than for Southeast Asia biomass burning (slope = 0.005) and East Asia outflow (0.011) pollution sources. Arrival of the plume high above Taiwan was confirmed by significant changes in signature aerosol properties. Thus, with critical observational evidence, our study reported for the first time enhanced mercury levels ∼18000 km downwind from a volcano source, providing an important check on volcanic Hg emission strength. [Display omitted] • Long-range transport of La Soufrière volcano plume to western North Pacific. • First time volcanic Hg reported ∼18000 km downwind of eruption. • Significant changes in signature columnar aerosol optical properties were also observed. [ABSTRACT FROM AUTHOR]

Gas-particle partitioning of oxidized mercury (Hg) plays an important role in governing the speciation, transport and deposition of atmospheric Hg. Although studies on gas-particle partitioning of oxidized Hg have been conducted at some urban sites, comparable studies at remote mountain sites are still limited. This study analyzes multi-year (2014–2016) data of speciated atmospheric Hg concentrations from Lulin Atmospheric Background Station (LABS, 2862 m above sea level), Taiwan, to explore the factors that influence the gas-particle partitioning of atmospheric oxidized Hg. Mean concentrations (±S.D.) of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate-bound mercury (PBM) were 1.54 ± 0.34 ng m−3, 14.5 ± 26.5 pg m−3, and 5.0 ± 12.0 pg m−3, respectively. In addition, our results indicated that the partitioning of Hg(II) toward particles was favored in the upper free troposphere and/or lower stratosphere. Both temperature (T) and relative humidity (RH) were found to strongly affect the gas-particle partitioning of oxidized Hg. Significant negative correlations between the partitioning coefficient (K p) and T were obtained for all seasons, but peaked in summer. When RH<30%, K p decreased with increasing RH. However, K p and RH were positively correlated when RH>30%. Two empirical K p -T and K p -T-RH regression equations: log(1/ K p) = 15.0 – 3887.6(1/T) and log(1/ K p) = 17.92 – 4390.0(1/T) – 0.016RH were developed for free tropospheric air downwind of continental East Asia, which could be implemented in a chemical transport model to improve our understanding of the Hg biogeochemical cycle. [Display omitted] • Gas-particle partitioning of Hg(II) was characterized at a mountain site in East Asia. • Partitioning coefficient (K p) correlated with temperature negatively. • K p increased with increasing relative humidity (RH) when RH>30%. • However, K p decreased with increasing RH when RH<30%. • Partitioning of Hg(II) toward particles was favored in the upper free troposphere. [ABSTRACT FROM AUTHOR]

Gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), particulate-bound mercury (PBM), and the isotopic composition of total gaseous mercury (TGM = GEM + GOM) were measured at the Lulin Atmospheric Background Station (LABS), a mountain background site downwind of the East Asia continent, from February 2015 to January 2016. Mean (±S.D.) concentrations of GEM, GOM, and PBM were 1.54 ± 0.34 ng m−3, 14.0 ± 27.8 pg m−3, and 2.6 ± 3.7 pg m−3, respectively. Concentration-Weighted Trajectory (CWT) analysis indicated that East and coastal China were the main source regions of elevated GEM observed at LABS. Weekly integrated TGM showed significant variations in δ202Hg TGM (−0.42 to 0.41‰) and Δ199Hg TGM (−0.31 to −0.13‰). Both δ202Hg TGM and Δ199Hg TGM showed clear seasonal variations, but the seasonal pattern of δ202Hg TGM was different from that of Δ199Hg TGM. The lowest mean δ202Hg TGM was observed in spring (−0.15‰), while the lowest mean Δ199Hg TGM was observed in summer (−0.24‰). A significant positive correlation (R2 = 0.38, p < 0.01) existed between δ202Hg TGM and normalized difference vegetation index (NDVI), suggesting vegetation activity was an important factor controlling the seasonal variation of δ202Hg TGM. In contrast, air mass transport path, which influences the source region of TGM to LABS, was likely the driver for the seasonal variations of Δ199Hg TGM. Furthermore, results from the air mass classification showed distinguishable Δ199Hg TGM signature for different air mass source regions, with air masses from South China Sea and western Pacific Ocean being characterized by more negative Δ199Hg TGM (−0.25 ± 0.04‰). Results of this research demonstrated a clear difference in isotopic compositions of atmospheric Hg between continental and marine air masses. Image 1 • The first TGM isotope data reported from a mountain site downwind of East Asia. • Isotopic signature of TGM with air from open oceans had significant negative Δ199Hg. • Variability of δ202Hg TGM was attributed to vegetation activity. • Variation of Δ199Hg TGM was driven by air mass transport paths. [ABSTRACT FROM AUTHOR]

Concentrations of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particle-bound mercury (PBM) were measured at a suburban site in northern Taiwan between October 2017 and September 2018. Mean concentrations of GEM, GOM, and PBM were 2.61 ± 6.47 ng m−3, 12.1 ± 34.3 pg m−3, and 18.7 ± 86.8 pg m−3, respectively. On 35% of the days, elevated atmospheric mercury (Hg) concentration occurred between midnight and early morning when local wind direction shifted and came from sectors between SSW and S, indicating influence of local anthropogenic emission sources. As such, a diurnal pattern with nighttime peaks was observed for GEM, GOM, and PBM. However, elevated GOM values were also observed around noon on 87 occasions, coinciding with peak O 3 and solar radiation, suggesting additional contribution from in situ photochemical reactions. Seasonally, atmospheric Hg concentrations were higher in spring than in the other seasons. Besides the contribution from local emissions and the East Asian outflow, lower wind speed, cumulative rainfall, and days of rain in spring suggesting poor air dispersion and inefficient pollutant removal, hence leading to the accumulation of atmospheric Hg and thus higher concentrations. Two trans-boundary haze events from China were encountered during this study. Concentrations of GEM and PBM were enhanced on haze days, with particularly significant enhancement in PBM. Comparison of the maximum PBM values during these haze events to respective pre-event PBM values showed enhancements of 378% and 1438%, whereas enhancements of 100% and 147% were observed for GEM. GOM remained relatively low and stable during haze events, which could be due to the favored partitioning of GOM toward solid phase under high PM 2.5 concentrations and the lack of sunlight to fuel the photochemical production of GOM. Backward trajectories indicated that Hg emissions in east China likely contributed to the enhancements in atmospheric Hg concentrations measured at the suburban site in northern Taiwan during these two trans-boundary haze events. • Both local sources and regional transport contributed to the measured atmospheric Hg. • Two trans-boundary haze events from China were encountered. • Concentrations of GEM and PBM were enhanced on haze days, but GOM remained low. • Yangtze River Delta and east China were the Hg source regions for these haze events. [ABSTRACT FROM AUTHOR]