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Mercury (Hg) is a global atmospheric pollutant. In its oxidized form (HgII), it can readily deposit to ecosystems, where it may bioaccumulate and cause severe health effects. High HgII concentrations are reported in the free troposphere, but spatiotemporal data coverage is limited. Underestimation of HgII by commercially available measurement systems hinders quantification of Hg cycling and fate. During spring–summer 2021 and 2022, we measured elemental (Hg0) and oxidized Hg using a calibrated dual-channel system alongside trace gases, aerosol properties, and meteorology at the high-elevation Storm Peak Laboratory (SPL) above Steamboat Springs, Colorado. Oxidized Hg concentrations displayed diel and episodic behavior similar to previous work at SPL but were approximately 3 times higher in magnitude due to improved measurement accuracy. We identified 18 multi-day events of elevated HgII (mean enhancement of 36 pgm-3) that occurred in dry air (mean ± SD of relative humidity = 32 ± 16 %). Lagrangian particle dispersion model (HYSPLIT–STILT, Hybrid Single-Particle Lagrangian Integrated Trajectory–Stochastic Time-Inverted Lagrangian Transport) 10 d back trajectories showed that the majority of transport prior to events occurred in the low to middle free troposphere. Oxidized Hg was anticorrelated with Hg0 during events, with an average (± SD) slope of - 0.39 ± 0.14. We posit that event HgII resulted from upwind oxidation followed by deposition or cloud uptake during transport. Meanwhile, sulfur dioxide measurements verified that three upwind coal-fired power plants did not influence ambient Hg at SPL. Principal component analysis showed HgII consistently inversely related to Hg0 and generally not associated with combustion tracers, confirming oxidation in the clean, dry free troposphere as its primary origin. [ABSTRACT FROM AUTHOR]

Southern sea otters (Enhydra lutris nereis) are a federally listed threatened keystone species of the California kelp forest ecosystem and a sentinel species, indicating environmental health. Mercury (Hg) is a bioaccumulative neurotoxin that poses a threat to high trophic‐level species such as marine mammals. We quantified total Hg (THg) concentrations in fur, brain, and liver tissues of necropsied southern sea otters (n = 44) that stranded along the California coast from 2010 to 2019. THg concentrations differed significantly between fur and brain, and between liver and brain. Tissue type explained 64%, and sex explained only 3.3% of overall THg variability (0.48–46.1 μg/g dry weight). All individuals had liver Hg concentrations measuring well under the proposed lower‐limit low risk guideline for harp seals, Pagophilus groenlandicus. However, six sea otters exceeded the liver THg moderate risk threshold for terrestrial furbearers to which sea otters are closely related. These data represent baseline THg concentrations in fur, brain, and liver of the southern sea otter and build upon previous studies in various sea otter subspecies. Research on sea otter Hg tolerance and continued monitoring are needed to clarify potential health risks associated with the tissue concentrations observed in this study. [ABSTRACT FROM AUTHOR]

Mercury (Hg) is a global atmospheric pollutant. In its oxidized form (HgII), atmospheric Hg can readily deposit to ecosystems, where it may bioaccumulate and cause severe health effects. High HgII concentrations are reported in the free troposphere, but spatiotemporal data coverage is limited. Underestimation of HgII by commercially available measurement systems hinders quantification of Hg cycling and fate. During spring-summer 2021 and 2022, we measured elemental (Hg0) and oxidized Hg using a calibrated dual-channel system alongside trace gases, aerosol properties, and meteorology at the high-elevation Storm Peak Laboratory (SPL) above Steamboat Springs, Colorado. Oxidized Hg concentrations displayed temporal behavior similar to previous work at SPL, but were approximately three times higher in magnitude due to improved measurement accuracy. We identified 18 multi-day events of elevated HgII (mean enhancement: 36 pg m-3) that occurred in dry air (mean ± s.d. RH = 32 ± 16 %). Lagrangian particle dispersion model (HYSPLIT-STILT) 10-day back-trajectories showed that the majority of transport prior to events occurred in the low to mid-free troposphere. Oxidized Hg was anticorrelated with Hg0 during events, with an average (± s.d.) slope of -0.39 ± 0.14, suggestive of upwind oxidation followed by deposition during transport. Concurrent sulfur dioxide measurements verified that three upwind coal-fired power plants did not measurably contribute ambient Hg at SPL. Principal Components Analysis revealed HgII consistently inversely related with Hg0 and was generally not associated with combustion tracers, confirming oxidation in the clean, dry free troposphere as its primary origin. [ABSTRACT FROM AUTHOR]

Total airborne mercury (TAM) and carbon monoxide (CO) were measured in 22 pollution transport “events” at Mt. Bachelor Observatory (MBO), USA (2.8km asl) between March 2004 and September 2005. Submicron particulate scattering (, ozone (, and nitrogen oxides ( were also measured and enhancement ratios for each chemical and aerosol species with CO were calculated. Events were categorized based on their source regions, which were determined by a combination of back trajectories, satellite fire detections, chemical and aerosol enhancement ratios, and meteorology. The mean values for each source region are: East Asian industrial (, events, 236h), Pacific Northwest U.S. (PNW) biomass burning (, events, 173h), and Alaska biomass burning (, events, 96h). The means from Asian long-range transport (ALRT) and biomass burning events are combined with previous estimates of CO emissions from Chinese anthropogenic, global biomass burning, and global boreal biomass sources in order to estimate the emissions of gaseous elemental mercury (GEM) from these sources. The GEM emissions that we calculate here are: Chinese anthropogenic (), global biomass burning , and global boreal biomass burning , with errors estimated from propagating the uncertainty in the mean enhancement ratios and CO emissions. A comparison of our results with published mercury (Hg) emissions inventories reveals that the Chinese GEM emissions from this study are higher by about a factor of two, while our estimate for global biomass burning is consistent with previous studies. [Copyright &y& Elsevier]

Abstract: Emissions inventories indicate that Asian Hg sources are more than 50% of the global anthropogenic total. However, few measurements have been made to verify these large emissions. In this paper, we report on measurements of mercury from two sites during spring 2004 which received Asian outflow: Hedo Station, Okinawa (HSO), Japan and the Mt. Bachelor Observatory (MBO) in central Oregon, USA. At both sites, export of atmospheric mercury from China and East Asia was verified by the observations and meteorological data. The mean Hg0 concentration we observed at HSO was 2.04ngm−3, which is significantly higher than the global background. Measurements of reactive gaseous mercury and particulate mercury at HSO found relatively little outflow of these compounds from Asia, generally less than 3% of the total mercury. By examining the correlation of Hg0 to carbon monoxide during outflow events, we have derived an enhancement ratio, which should reflect the ratio of these compounds in the source region. During outflow from Asia, the mean Hg0/CO molar enhancement ratio we observed at HSO was 6.2×10−7, which is nearly twice the expected ratio based on emissions estimates from China. During one episode of long-range transport from Asia to the MBO, we found a very similar ratio of Hg0/CO to that observed at HSO and a similar ratio was also reported by Friedli et al. (2004, Journal of Geophysical Research 109, D19 S25) downwind of Shanghai. Thus the ratio of Hg0/CO appears to be a good tracer of Asian industrial outflow. Using the Hg0/CO ratio and a recent inventory for CO emissions, we calculate Hg0 emissions from Asia of 1460 metric tonsyear−1, which is nearly two times the value in the Pacyna et al. (2003, Global mercury emissions. Presented at Long-Range Transport Workshop, Ann Arbor, MI, September 2003) inventory. Several hypotheses are proposed to explain this discrepancy, including an underestimation of the Chinese industrial Hg0 emissions, natural sources, significant re-emissions of previously deposited Hg and/or a higher ratio of Hg0/total Hg in the outflow from Asia than in the emission inventory. [Copyright &y& Elsevier]