In:
Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 117, No. 49 ( 2020-12-08), p. 30949-30956
Abstract:
Mercury (Hg), a global contaminant, is emitted mainly in its elemental form Hg 0 to the atmosphere where it is oxidized to reactive Hg II compounds, which efficiently deposit to surface ecosystems. Therefore, the chemical cycling between the elemental and oxidized Hg forms in the atmosphere determines the scale and geographical pattern of global Hg deposition. Recent advances in the photochemistry of gas-phase oxidized Hg I and Hg II species postulate their photodissociation back to Hg 0 as a crucial step in the atmospheric Hg redox cycle. However, the significance of these photodissociation mechanisms on atmospheric Hg chemistry, lifetime, and surface deposition remains uncertain. Here we implement a comprehensive and quantitative mechanism of the photochemical and thermal atmospheric reactions between Hg 0 , Hg I , and Hg II species in a global model and evaluate the results against atmospheric Hg observations. We find that the photochemistry of Hg I and Hg II leads to insufficient Hg oxidation globally. The combined efficient photoreduction of Hg I and Hg II to Hg 0 competes with thermal oxidation of Hg 0 , resulting in a large model overestimation of 99% of measured Hg 0 and underestimation of 51% of oxidized Hg and ∼66% of Hg II wet deposition. This in turn leads to a significant increase in the calculated global atmospheric Hg lifetime of 20 mo, which is unrealistically longer than the 3–6-mo range based on observed atmospheric Hg variability. These results show that the Hg I and Hg II photoreduction processes largely offset the efficiency of bromine-initiated Hg 0 oxidation and reveal missing Hg oxidation processes in the troposphere.
Type of Medium:
Online Resource
ISSN:
0027-8424
,
1091-6490
DOI:
10.1073/pnas.1922486117
Language:
English
Publisher:
Proceedings of the National Academy of Sciences
Publication Date:
2020
detail.hit.zdb_id:
209104-5
detail.hit.zdb_id:
1461794-8
SSG:
11
SSG:
12
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