Mercury Speciation at a Coastal Site in the Northern Gulf of Mexico: Results from the Grand Bay Intensive Studies in Summer 2010 and Spring 2011

Abstract

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 O 3 , SO 2 , CO, NO, NO Y , 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 ) were observed on a few days in each study and were usually associated with either elevated O 3 (>50 ppbv), BrO, and solar radiation or elevated SO 2 (>a few ppbv) but lower O 3 (~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 ( 7 Be) 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.

Overview of receptor-based source apportionment studies for speciated atmospheric mercury

“…The Canadian sites are located in Point Petre and Egbert, Ontario (Blanchard et al, 2002); CAMNet stations (Temme et al, 2007), Toronto (Cheng et al, 2009), northwestern Ontario (Cheng et al, 2012); Kejimkujik National Park (Cheng et al, 2013a); Flin Flon, Manitoba (Eckley et al, 2013); Fort McMurray, Alberta (Parsons et al, 2013); and Windsor, Ontario (Xu et al, 2014). The US sites included south Florida (Graney et al, 2004); Detroit, Michigan (Lynam and Keeler, 2006;Liu et al, 2007); Mount Bachelor, Oregon (Swartzendruber et al, 2006); Athens, Ohio (Gao, 2007); Rochester, New York (Huang et al, 2010); and Grand Bay, Mississippi (Ren et al, 2014). Most of the studies identified a factor/component that was representative of combustion sources (e.g., coal combustion, vehicular, industrial, biomass burning, and waste incineration emissions) regardless of whether the studies were conducted in urban, rural, or coastal locations.…”

“…This component included strong positive component loadings on GOM, O 3 , temperature and wind speed, and negative loadings on relative humidity (Lynam and Keeler, 2006). Other studies also extracted a component representative of GEM oxidation with similar pollutant or meteorological parameter loadings; however, the component did not explain the most variance with percentages ranging from 11 to 27 % (Li et al, 2008;Huang et al, 2010;Cheng et al, 2012Cheng et al, , 2013aRen et al, 2014;Xu et al, 2014). GEM oxidation was also inferred from a PCA component containing GOM, BrO and O 3 (Ren et al, 2014).…”

“…Other studies also extracted a component representative of GEM oxidation with similar pollutant or meteorological parameter loadings; however, the component did not explain the most variance with percentages ranging from 11 to 27 % (Li et al, 2008;Huang et al, 2010;Cheng et al, 2012Cheng et al, , 2013aRen et al, 2014;Xu et al, 2014). GEM oxidation was also inferred from a PCA component containing GOM, BrO and O 3 (Ren et al, 2014). Although BrO and O 3 are potential oxidants of GEM, it is unclear from this component whether the oxidation reaction was dominated by BrO or O 3 and occurring in the gas, liquid, and/or solid phase.…”

Airborne Vertical Profiling of Mercury Speciation near Tullahoma, TN, USA

“…The system was operated according to National Atmospheric Deposition Program Atmospheric's (NADP) Mercury Network (AMNet) protocol [31], except a shorter sample/analysis period (2.5 min) was used. The system was located next to a hangar where the aircraft parked.…”

Meteorological Modeling Using the WRF-ARW Model for Grand Bay Intensive Studies of Atmospheric Mercury

“…The Great Lakes region has been one focus of study [2][3][4], while mercury pollution in the Gulf of Mexico region has also drawn increasing attention in recent years [5]. The observed atmospheric wet deposition flux of mercury in the Gulf of Mexico region is higher than that in any other region in the United States [6][7][8]. This is at least partly due to the relatively high rainfall rates in the region, as well as the higher prevalence of tall convective thunderstorms, resulting in the increased scavenging of free tropospheric mercury [9].…”