Abstract
During two intensive studies in summer 2010 and spring 2011, measurements of mercury species including gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate-bound mercury (PBM), trace chemical species including O3, SO2, CO, NO, NOY, and black carbon, and meteorological parameters were made at an Atmospheric Mercury Network (AMNet) site at the Grand Bay National Estuarine Research Reserve (NERR) in Moss Point, Mississippi. Surface measurements indicate that the mean mercury concentrations were 1.42 ± 0.12 ng∙m−3 for GEM, 5.4 ± 10.2 pg∙m−3 for GOM, and 3.1 ± 1.9 pg∙m−3 for PBM during the summer 2010 intensive and 1.53 ± 0.11 ng∙m−3 for GEM, 5.3 ± 10.2 pg∙m−3 for GOM, and 5.7 ± 6.2 pg∙m−3 for PBM during the spring 2011 intensive. Elevated daytime GOM levels (>20 pg∙m−3) were observed on a few days in each study and were usually associated with either elevated O3 (>50 ppbv), BrO, and solar radiation or elevated SO2 (>a few ppbv) but lower O3 (~20–40 ppbv). This behavior suggests two potential sources of GOM: photochemical oxidation of GEM and direct emissions of GOM from nearby local sources. Lack of correlation between GOM and Beryllium-7 (7Be) suggests little influence on surface GOM from downward mixing of GOM from the upper troposphere. These data were analyzed using the HYSPLIT back trajectory model and principal component analysis in order to develop source-receptor relationships for mercury species in this coastal environment. Trajectory frequency analysis shows that high GOM events were generally associated with high frequencies of the trajectories passing through the areas with high mercury emissions, while low GOM levels were largely associated the trajectories passing through relatively clean areas. Principal component analysis also reveals two main factors: direct emission and photochemical processes that were clustered with high GOM and PBM. This study indicates that the receptor site, which is located in a coastal environment of the Gulf of Mexico, experienced impacts from mercury sources that are both local and regional in nature.
Highlights
Mercury (Hg) is a ubiquitous and toxic pollutant in the environment
We found that the decrease of gaseous elemental mercury (GEM) we observed occurred typically in the morning before sunrise when relative humidity was typically the highest of the day, which is consistent with observations of [12] and [14], but different from the afternoon events observed by [16]
This is consistent with two possible processes that could lead to elevated gaseous oxidized mercury (GOM) levels: (1) photochemical conversion of GEM under conditions when ozone levels are high during the midday, and (2) direct emissions of GOM from local emission sources in which high SO2 levels were present
Summary
Mercury (Hg) is a ubiquitous and toxic pollutant in the environment. It exists in several distinct chemical and physical forms that dictate to a large degree, the ultimate impact of Hg on the environment. The release of mercury compounds to the atmosphere, followed by their transport and deposition, often constitutes the main pathway for the global dispersion of mercury and the dominant loading mechanism of new mercury to water bodies and watersheds [1,2,3,4]. Human activities, such as smelting and coal burning, have significantly increased mercury levels in the atmosphere, surface soils, fresh waters, and oceans [2,5,6]. Human exposure to mercury is primarily from the consumption of contaminated fish and other aquatic organisms [5,8,9]
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