Abstract. The tundra plays a pivotal role in the Arctic mercury(Hg) cycle by storing atmospheric Hg deposition and shuttling it to theArctic Ocean. A recent study revealed that 70 % of the atmospheric Hgdeposition to the tundra occurs through gaseous elemental mercury (GEM or Hg(0))uptake by vegetation and soils. Processes controlling land–atmosphereexchange of Hg(0) in the Arctic tundra are central, but remainunderstudied. Here, we combine Hg stable isotope analysis of Hg(0) in theatmosphere, interstitial snow air, and soil pore air, with Hg(0) fluxmeasurements in a tundra ecosystem at Toolik Field Station in northernAlaska (USA). In the dark winter months, planetary boundary layer (PBL)conditions and Hg(0) concentrations were generally stable throughout the dayand small Hg(0) net deposition occurred. In spring, halogen-inducedatmospheric mercury depletion events (AMDEs) occurred, with the fastre-emission of Hg(0) after AMDEs resulting in net emission fluxes of Hg(0).During the short snow-free growing season in summer, vegetation uptake ofatmospheric Hg(0) enhanced atmospheric Hg(0) net deposition to the Arctictundra. At night, when PBL conditions were stable, ecosystem uptake ofatmospheric Hg(0) led to a depletion of atmospheric Hg(0). The night-timedecline of atmospheric Hg(0) was concomitant with a depletion of lighterHg(0) isotopes in the atmospheric Hg pool. The enrichment factor,ε202Hgvegetationuptake=-4.2 ‰ (±1.0 ‰) was consistentwith the preferential uptake of light Hg(0) isotopes by vegetation. Hg(0)flux measurements indicated a partial re-emission of Hg(0) during daytime,when solar radiation was strongest. Hg(0) concentrations in soil pore airwere depleted relative to atmospheric Hg(0) concentrations, concomitant withan enrichment of lighter Hg(0) isotopes in the soil pore air, ε202Hgsoilair-atmosphere=-1.00 ‰(±0.25 ‰) and E199Hgsoilair-atmosphere=0.07 ‰ (±0.04 ‰). Thesefirst Hg stable isotope measurements of Hg(0) in soil pore air areconsistent with the fractionation previously observed during Hg(0) oxidationby natural humic acids, suggesting abiotic oxidation as a cause for observedsoil Hg(0) uptake. The combination of Hg stable isotope fingerprints withHg(0) flux measurements and PBL stability assessment confirmed a dominantrole of Hg(0) uptake by vegetation in the terrestrial–atmosphere exchange ofHg(0) in the Arctic tundra.
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This content will become publicly available on October 12, 2024
Observed in-plume gaseous elemental mercury depletion suggests significant mercury scavenging by volcanic aerosols
Terrestrial volcanism is known to emit mercury (Hg) into the atmosphere. However, despite many years of investigation, its net impact on the atmospheric Hg budget remains insufficiently constrained, in part because the transformations of Hg in volcanic plumes as they age and mix with background air are poorly understood. Here we report the observation of complete gaseous elemental mercury (GEM) depletion events in dilute and moderately aged (∼3–7 hours) volcanic plumes from Piton de la Fournaise on Réunion Island. While it has been suggested that co-emitted bromine could, once photochemically activated, deplete GEM in a volcanic plume, we measured low bromine concentrations in both the gas- and particle-phase and observed complete GEM depletion even before sunrise, ruling out a leading role of bromine chemistry here. Instead, we hypothesize that the GEM depletions were mainly caused by gas–particle interactions with sulfate-rich volcanic particles (mostly of submicron size), abundantly present in the dilute plume. We consider heterogeneous GEM oxidation and GEM uptake by particles as plausible manifestations of such a process and derive empirical rate constants. By extrapolation, we estimate that volcanic aerosols may scavenge 210 Mg y−1 (67–480 Mg y−1) of Hg from the atmosphere globally, acting effectively as atmospheric mercury sink. While this estimate is subject to large uncertainties, it highlights that Hg transformations in aging volcanic plumes must be better understood to determine the net impact of volcanism on the atmospheric Hg budget and Hg deposition pathways.
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- Award ID(s):
- 1951514
- NSF-PAR ID:
- 10497890
- Publisher / Repository:
- Environmental Science: Atmospheres
- Date Published:
- Journal Name:
- Environmental Science: Atmospheres
- Volume:
- 3
- Issue:
- 10
- ISSN:
- 2634-3606
- Page Range / eLocation ID:
- 1418 to 1438
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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