Sources and Transformation Mechanisms of Atmospheric Particulate Bound Mercury Revealed by Mercury Stable Isotopes

Abstract

This study examined the isotopic composition of particulate bound mercury (PBM) in 10 Chinese megacities and explored the associated sources and transformation mechanisms. PBM in these cities was characterized by negative δ202Hg (mean: −2.00 to −0.78‰), slightly negative to highly positive Δ199Hg (mean: −0.04 to 0.47‰), and slightly positive Δ200Hg (mean: 0.02 to 0.06‰) values. The positive PBM Δ199Hg signatures were likely caused by physiochemical reactions in aerosols. The Δ199Hg/Δ201Hg ratio varied from 0.94 to 1.39 in the cities and increased with the increase in the corresponding mean Δ199HgPBM value. We speculate that, in addition to the photoreduction of oxidized Hg, other transformation mechanisms in aerosols (e.g., isotope exchange, complexation, and oxidation, which express nuclear volume effects) also shape the Δ199HgPBM signatures in the present study. These processes are likely enhanced in the presence of strong gas-particle partitioning of gaseous oxidized Hg (GOM) and elevated levels of redox active metals (e.g., Fe), halides, and elemental carbon. Based on Δ200HgPBM data presented in this and previous studies, we estimate that large proportions (∼47 ± 22%) of PBM were sourced from the oxidation of gaseous elemental Hg followed by the partitioning of GOM onto aerosols globally, indicating the transformation of Hg(0) to PBM as an important sink of atmospheric Hg(0).

Stable Isotopes Reveal Photoreduction of Particle-Bound Mercury Driven by Water-Soluble Organic Carbon during Severe Haze

“…Most physical and chemical processes lead to MDF, but odd-MIF is mainly produced by photochemical reactions (e.g. photoreduction of aqueous Hg­(II), photodemethylation of methylmercury). − Even-MIF is mainly observed in atmospheric samples, and its mechanism may be attributed to atmospheric redox processes. − Previous studies have reported Hg isotopes of PBM in different regions (e.g., urban, rural, and coastal areas) ,− and seasonal even diurnal variation of odd-MIF ,, and indicate that the isotopic compositions of PBM emitted from primary sources would be modified during atmospheric transformation or transportation. However, the mechanism that drives Hg isotope variations of PBM is still poorly understood, especially during the transformations of PBM in severe haze events.…”

Mercury evidence from southern Pangea terrestrial sections for end-Permian global volcanic effects

“…3h, i ), in which terrestrial Hg inputs are limited, provide a promising reservoir for tracking atmospheric fluxes of Hg 23 . For the pelagic Gujo-Hachiman section, the negative or near-zero Δ 199 Hg values associated with Hg concentration peaks near the LPME, document elevated fluxes of isotopically light Hg because Δ 199 Hg becomes more positive during atmospheric transport 24 . Combustion of terrestrial organic-rich sediments (e.g., coal 27 ), which can lead to elevated Hg concentrations 28 with a negative MIF in marine deposits 29 , was the likely dominant source of Hg at a global scale 14 (Fig.…”

“…1 ). These positive excursions were likely due to photoreduction of Hg(II) during long-distance transport through the atmosphere 24 . Moreover, the sharp decrease of pyrite sulfur isotope (δ 34 S) values coinciding with the extinction interval in the Bunnerong core provides evidence for increasing atmospheric sulfate concentrations, which have been previously linked to aerosol production by the STLIP 32 .…”

“…Although Δ 199 Hg has been widely used to track Hg sources during the Permian–Triassic transition 14 , 16 , 18 , interpretation of Hg isotopes in sediments can be complicated. Several factors influence Δ 199 Hg: (1) the proportions of Hg sourced from the mantle (near-zero MIF 22 ) versus organic-rich sediments by sills and/or combustion of vegetation and soil by wildfires (negative MIF 23 ); (2) the magnitude of Hg fractionation during atmospheric transport, which ranges from 0.1 to 0.8‰ in the modern atmosphere 24 ; and (3) mixing of multiple Hg sources, including terrestrial runoff, atmospheric removal, and seawater loading, in terrestrial and nearshore facies 16 , 17 , 25 , 26 . In Permian–Triassic successions, Δ 199 Hg shows large variations in different settings, with near-zero values in deep-shelf to slope settings but negative excursions in continental, shallow-shelf, deep-basinal, and pelagic settings (Fig.…”

Atmospheric Mercury Isotope Shifts in Response to Mercury Emissions from Underground Coal Fires

“…Before PBM samples were collected onto the filters, multiple atmospheric processes [e.g., oxidation of GEM to GOM followed by adsorption onto particulates, direct uptake of GEM, and photoreduction of Hg(II) in particulates] might occur and alter the isotope compositions of initial PBM sourced from anthropogenic emissions. 67 These processes could produce significant MIF, but their net effect typically imparts the collected PBM with positive odd-MIF values and Δ 199 Hg/Δ 201 Hg slopes of ∼1.0 [diagnostic of the magnetic isotope effect (MIE)] but sometimes up to 1.6 [diagnostic of the nuclear volume effect (NVE)]. 67 In addition, significant correlations of Δ 200 Hg versus Δ 199 Hg and Δ 204 Hg versus Δ 200 Hg were also typically observed in atmospheric samples (Figures 3D−F and 4D−F).…”