Abstract
Abstract. Receptor-based source apportionment studies of speciated atmospheric mercury are not only concerned with source contributions but also with the influence of transport, transformation, and deposition processes on speciated atmospheric mercury concentrations at receptor locations. Previous studies applied multivariate receptor models including principal components analysis and positive matrix factorization, and back trajectory receptor models including potential source contribution function, gridded frequency distributions, and concentration–back trajectory models. Combustion sources (e.g., coal combustion, biomass burning, and vehicular, industrial and waste incineration emissions), crustal/soil dust, and chemical and physical processes, such as gaseous elemental mercury (GEM) oxidation reactions, boundary layer mixing, and GEM flux from surfaces were inferred from the multivariate studies, which were predominantly conducted at receptor sites in Canada and the US. Back trajectory receptor models revealed potential impacts of large industrial areas such as the Ohio River valley in the US and throughout China, metal smelters, mercury evasion from the ocean and the Great Lakes, and free troposphere transport on receptor measurements. Input data and model parameters specific to atmospheric mercury receptor models are summarized and model strengths and weaknesses are also discussed. Multivariate models are suitable for receptor locations with intensive air monitoring because they require long-term collocated and simultaneous measurements of speciated atmospheric Hg and ancillary pollutants. The multivariate models provide more insight about the types of Hg emission sources and Hg processes that could affect speciated atmospheric Hg at a receptor location, whereas back trajectory receptor models are mainly ideal for identifying potential regional Hg source locations impacting elevated Hg concentrations. Interpretation of the multivariate model output to sources can be subjective and challenging when speciated atmospheric Hg is not correlated with ancillary pollutants and when source emissions profiles and knowledge of Hg chemistry are incomplete. The majority of back trajectory receptor models have not accounted for Hg transformation and deposition processes and could not distinguish between upwind and downwind sources effectively. Ensemble trajectories should be generated to take into account the trajectory uncertainties where possible. One area of improvement that applies to all the receptor models reviewed in this study is the greater focus on evaluating the accuracy of the models at identifying potential speciated atmospheric mercury sources, source locations, and chemical and physical processes in the atmosphere. In addition to receptor model improvements, the data quality of speciated atmospheric Hg plays an equally important part in producing accurate receptor model results.
Highlights
Gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particle-bound mercury (PBM) are the three forms of mercury that are found in the atmosphere
This paper provides a review of the major receptor-based methods used in the source apportionment of speciated atmospheric mercury, including a summary of the input data and model parameters used in receptor modeling of speciated atmospheric mercury and findings that may advance our understanding of mercury behavior in the atmosphere
Among the seven factors extracted from the Potsdam site, GEM was found in trace concentrations in one factor containing Se and S, which are characteristic of nickel smelting
Summary
Gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particle-bound mercury (PBM) are the three forms of mercury that are found in the atmosphere. One type of study is chemical transport modeling, which predicts speciated atmospheric Hg concentrations on regional and global scales based on the knowledge of source emissions, atmospheric dispersion and transport, and chemical and physical atmospheric processes. An alternative approach to studying source–receptor relationships is receptorbased methods In this type of study, receptor measurements (e.g., air concentrations, precipitation concentrations, or wet deposition) and back trajectory modeling are used separately and together to predict pollution sources and estimate the contributions of the sources to receptor measurements (Belis et al, 2013). Receptor-based methods do not require comprehensive knowledge of source emissions and mercury behavior in the atmosphere; they are less complicated than chemical transport models. The review is focused on five major receptor-based methodologies: principal components analysis, positive matrix factorization, potential source contribution function, gridded frequency distribution, and concentration–back trajectory models
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