Uncertainties in Atmospheric Mercury Modeling for Policy Evaluation

Abstract

Mercury (Hg) contamination is an issue of a growing environmental and public health concern. Atmospheric chemistry transport models for Hg are a critical tool for understanding the sources, processes, and fate of Hg. Uncertainties in multiple aspects of atmospheric Hg models, however, limit their application for policy evaluation and for monitoring global trends in atmospheric Hg concentrations. This review aims to identify uncertainties in atmospheric Hg modeling that are relevant in the context of policy and for informing decision-making. We focus on specific requirements of the Minamata Convention on Mercury, a global treaty signed in 2013 to protect human health and the environment from Hg, to demonstrate how existing uncertainties in atmospheric Hg modeling can influence our ability to evaluate source-receptor relationships. Modeling studies of source attribution suggest that major uncertainties in atmospheric Hg modeling arise from anthropogenic emissions, biogeochemical cycling, and atmospheric chemistry. Uncertainties in these aspects of modeling are expected to increase under the Convention, with regulation of anthropogenic emissions, changes in atmospheric conditions, and legacy and natural Hg source contribution to the global biogeochemical cycle. These uncertainties can interact with one another and with the current Hg species measurement capability and pose challenges to effectively monitoring trends in atmospheric Hg. Developing additional means to attribute simulated atmospheric Hg trends and improve source-receptor relationships in atmospheric Hg models would improve our ability to evaluate the Convention's effectiveness.

Subtropical subsidence and surface deposition of oxidized mercury produced in the free troposphere

“…Uncertainties in mercury modeling and chemistry have been recently reviewed by Gustin et al (2015), Ariya et al (2015), and Kwon and Selin (2016). Here we briefly discuss uncertainties which are pertinent to our study: uncertainties in the assumption of Br as the sole oxidant of Hg(0), in reduction kinetics of Hg(II), and in the assumed speciation of Hg (0) and Hg(II) in anthropogenic emissions.…”

Chemical cycling and deposition of atmospheric mercury in polar regions: review of recent measurements and comparison with models

“…Deposition is partly offset by the revolatilization of a fraction of deposited mercury. Large uncertainties associated with the models arise as a result of our incomplete understanding of atmospheric processes (e.g., oxidation pathways, deposition, and re-emission) (Kwon and Selin, 2016). Atmospheric mercury reactivity is exacerbated in high latitudes and there is still much to be learned from polar regions in terms of atmospheric processes.…”

Linking science and policy to support the implementation of the Minamata Convention on Mercury

“…The use and interpretation of outcome indicators to measure effectiveness pose an ongoing scientific challenge. Despite extensive efforts to understand the Hg cycle, scientific uncertainties, and environmental variabilities limit the ability to link global changes in Hg emissions to environmental concentrations and exposures, and obscure the ability to attribute these changes to Minamata Convention-related implementation measures (Selin 2014b ; Kwon and Selin 2016 ; Obrist et al 2018 ). To address these uncertainties, there is a need to collect more empirical data on Hg emissions and concentrations over longer time periods and geographical areas, on environmental factors that affect atmospheric transport and biogeochemical cycling, and on the factors that drive changes in Hg bioaccumulation, biomagification, exposure, and toxicity.…”