Abstract
Abstract. Atmospheric chemistry and transport of mercury play a key role in the global mercury cycle. However, there are still considerable knowledge gaps concerning the fate of mercury in the atmosphere. This is the second part of a model intercomparison study investigating the impact of atmospheric chemistry and emissions on mercury in the atmosphere. While the first study focused on ground-based observations of mercury concentration and deposition, here we investigate the vertical and interhemispheric distribution and speciation of mercury from the planetary boundary layer to the lower stratosphere. So far, there have been few model studies investigating the vertical distribution of mercury, mostly focusing on single aircraft campaigns. Here, we present a first comprehensive analysis based on various aircraft observations in Europe, North America, and on intercontinental flights. The investigated models proved to be able to reproduce the distribution of total and elemental mercury concentrations in the troposphere including interhemispheric trends. One key aspect of the study is the investigation of mercury oxidation in the troposphere. We found that different chemistry schemes were better at reproducing observed oxidized mercury patterns depending on altitude. High concentrations of oxidized mercury in the upper troposphere could be reproduced with oxidation by bromine while elevated concentrations in the lower troposphere were better reproduced by OH and ozone chemistry. However, the results were not always conclusive as the physical and chemical parameterizations in the chemistry transport models also proved to have a substantial impact on model results.
Highlights
At the time of publication the Minamata Convention has 128 signatories and has been ratified by 55 countries
Inside the planetary boundary layer (PBL), oxidized mercury (OM) concentrations are very low and mostly between 20 and 100 pg m−3 in Europe and North America, even in source regions with high anthropogenic emissions (Xu et al, 2016; Weigelt et al, 2016; 2013; Gay et al, 2013; Tørseth et al, 2012; Prestbo and Gay, 2009; Weiss-Penzias et al, 2015)
In China, particulate bound mercury (PBM) concentrations up to 1000 pg m3 and gaseous oxidized mercury (GOM) concentrations up to 100 pg m3 have been observed, but no aircraft observations in the PBL and the lower free troposphere (LFT) are available for this region : (Fu et al, 2015, 2016; Sprovieri et al, 2016)
Summary
At the time of publication the Minamata Convention has 128 signatories and has been ratified by 55 countries. The state of mercury contamination is typically determined by measurement of the relevant mercury species (e.g., total mercury (TM) in the atmosphere, methylmercury in fish). In order to understand the sources of mercury pollution and to predict the impact of various possible measures for mercury emission reduction it is necessary to apply complex chemistry transport models. The main question is how elemental mercury emitted from anthropogenic, natural, and legacy sources is oxidized. This includes the relative importance of oxidizing reaction partners and the relevance of reduction pathways of oxidized mercury under environmental conditions. Once we understand the redox processes of atmospheric mercury, is it possible to determine the range of mercury transport and the fate of mercury emitted in the past and the future
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