Open AccessImproved Mechanistic Model of the Atmospheric Redox Chemistry of Mercury
Author(s) -
Viral Shah,
Daniel Jacob,
Colin P. Thackray,
Xuan Wang,
Elsie M. Sunderland,
Theodore S. Dibble,
Alfonso SaizLopez,
Ivan Černušák,
Vladimı́r Kellö,
Pedro J. Castro,
Rongrong Wu,
Chuji Wang
Publication year - 2021
Publication title -
environmental science and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.851
H-Index - 397
eISSN - 1520-5851
pISSN - 0013-936X
DOI - 10.1021/acs.est.1c03160
Subject(s) - photodissociation , chemistry , atmospheric chemistry , ozone , aqueous solution , troposphere , radical , deposition (geology) , mercury (programming language) , aerosol , redox , environmental chemistry , inorganic chemistry , photochemistry , meteorology , organic chemistry , paleontology , physics , sediment , computer science , biology , programming language
We present a new chemical mechanism for Hg 0 /Hg I /Hg II atmospheric cycling, including recent laboratory and computational data, and implement it in the GEOS-Chem global atmospheric chemistry model for comparison to observations. Our mechanism includes the oxidation of Hg 0 by Br and OH, subsequent oxidation of Hg I by ozone and radicals, respeciation of Hg II in aerosols and cloud droplets, and speciated Hg II photolysis in the gas and aqueous phases. The tropospheric Hg lifetime against deposition in the model is 5.5 months, consistent with observational constraints. The model reproduces the observed global surface Hg 0 concentrations and Hg II wet deposition fluxes. Br and OH make comparable contributions to global net oxidation of Hg 0 to Hg II . Ozone is the principal Hg I oxidant, enabling the efficient oxidation of Hg 0 to Hg II by OH. BrHg II OH and Hg II (OH) 2 , the initial Hg II products of Hg 0 oxidation, respeciate in aerosols and clouds to organic and inorganic complexes, and volatilize to photostable forms. Reduction of Hg II to Hg 0 takes place largely through photolysis of aqueous Hg II -organic complexes. 71% of model Hg II deposition is to the oceans. Major uncertainties for atmospheric Hg chemistry modeling include Br concentrations, stability and reactions of Hg I , and speciation and photoreduction of Hg II in aerosols and clouds.