Recent Advances in Atmospheric Chemistry of Mercury

Abstract

Mercury is one of the most toxic metals and has global importance due to the biomagnification and bioaccumulation of organomercury via the aquatic food web. The physical and chemical transformations of various mercury species in the atmosphere strongly influence their composition, phase, transport characteristics and deposition rate to the ground. Modeling efforts to evaluate the mercury cycling in the environment require an accurate understanding of atmospheric mercury chemistry. We focus this article on recent studies (since 2015) on improving our understanding of the atmospheric chemistry of mercury. We discuss recent advances in (i) determining the dominant atmospheric oxidant of elemental mercury (Hg 0 ); (ii) understanding the oxidation reactions of Hg 0 by halogen atoms and by nitrate radical (NO 3 ); (iii) the aqueous reduction of oxidized mercury compounds (Hg II ); and (iv) the heterogeneous reactions of Hg on atmospherically-relevant surfaces. The need for future research to improve understanding of the fate and transformation of mercury in the atmosphere is also discussed.

Photodissociation Mechanisms of Major Mercury(II) Species in the Atmospheric Chemical Cycle of Mercury

“…Even though earlier schemes considered oxidation by O 3 as the main pathway in the atmosphere, it was later reported that this reaction is irrelevant in the atmosphere as the gas‐phase reaction is too slow . Since then, the reaction with very reactive bromine atoms is widely assumed to command Hg oxidation globally even though they are present at a low concentration only . The radical produced, HgBr, is an intermediate that can then thermally dissociate back to Hg 0 or be further oxidized by atmospheric radicals such as OH, Br, I, Cl, NO 2 , HO 2 , BrO, IO, and ClO, to form stable Hg II compounds …”

Is oxidation of atmospheric mercury controlled by different mechanisms in the polluted continental boundary layer vs. remote marine boundary layer?

“…These large uncertainties in atmospheric mercury oxidation are related not only to the rate constants of related reactions, but also to the chemical pathways themselves (Si and Ariya 2018). While early modeling of GEM oxidation in the troposphere accounted for a high impact of photochemical smog by considering ozone (O 3 ) and hydroxyl radical (OH) as major GEM oxidants (Seigneur et al 1994, Lin andPongprueksa 2007), more recent modeling studies indicate a major role for the bromine atom (Br) in GEM oxidation on a global scale, and particularly in the marine boundary layer and free troposphere (Lin et al 2004, Holmes et al 2006, 2010.…”

Correction: Recent Advances in Atmospheric Chemistry of Mercury

“…The published paper [1] has been updated to remove instances of copied text from other publications [2][3][4][5][6]. Changes have been made throughout the paper, with the most significant alterations made in Sections 2.1, 2.4, 3.1, 3.2, 3.3, and 4.…”

“…Ref. [1] is a review article that was invited for the journal Atmosphere. The author Lin Si took the lead in writing the article, although this is the first time she has undertaken writing a review paper.…”

“…This Correction was deemed necessary to avoid the impression that the text presented in [1] was the original work of the authors. The Editorial Office accepts that the authors did not intend to misrepresent the work, however, the original wording did not make it sufficiently clear that a number of passages were direct quotations.…”