Comparison of Atmospheric Mercury Speciation at a Coastal and an Urban Site in Southeastern Texas, USA

Abstract

Sixteen months of continuous measurements and the analysis of atmospheric mercury (gaseous elemental mercury GEM, gaseous oxidized mercury GOM, and particulate bound mercury PBM) under urban and coastal settings were conducted in Southeastern Texas. At the urban site, the GEM mean mixing ratio was 185 ppqv, 5%–10% higher than the Northern Hemisphere GEM background level. GOM and PBM mixing ratios were as much as six times higher than their background level. The coastal site GEM mean mixing ratio was 165 ppqv, higher than other coastal sites located in the Northern Hemisphere. GOM and PBM mean mixing ratios at the coastal site were 0.75 ppqv and 0.58 ppqv. The urban site had a higher frequency of high mercury events (>300 ppqv) compared to the coastal site. The diurnal patterns were found for both sites: In the urban environment, GEM accumulated to the maximum mixing ratio just after sunrise and decreased to the minimum mixing ratio in late afternoon. In the coastal environment, GEM decreased at night reaching its minimum mixing ratio before sunrise. The relationship between atmospheric mercury species and meteorological parameters was investigated. An examination of the relationship between atmospheric mercury species and key trace gases was conducted as well, showing that the concurrence of GEM, CO2, CO, CH4, and SO2 maximum mixing ratios was notable and provided evidence they may originate from the same emission source. The coastal site was at times influenced by polluted air from urban Houston and the cleaner Gulf of Mexico marine air at other times.

Spatial and Temporal Trends of Gaseous Elemental Mercury over a Highly Impacted Coastal Environment (Northern Adriatic, Italy)

“…In this urban site, no relevant sources of contamination are known, thus GEM could largely be carried from contaminated areas by wind during the diurnal sea breeze. The influence of sea breezes on atmospheric GEM levels in urban areas is well documented [17,25,61,64]. The wind rose chart shows that when GEM is high (up to an hourly mean value of 8 ng m -3 ) with winds prevalently blowing from W and NW, in the direction of the highly contaminated Fossalon plain, it (GEM) could reach the city of Trieste via the seawater surface of the Gulf (Figure 5).…”

“…The occurrence of events of high atmospheric GEM levels is usually associated with conditions of stagnant air and low atmospheric mixing as shown in Figure 4 [17,59].…”

“…In this urban site, no relevant sources of contamination are known, thus GEM could largely be carried from contaminated areas by wind during the diurnal sea breeze. The influence of sea breezes on atmospheric GEM levels in urban areas is well documented [17,25,61,64].…”

“…Mercury occurs in the atmosphere in three different forms, operationally identified as gaseous elemental Hg (GEM), reactive gaseous Hg (RGM) and particulate bound Hg (PBM) [15]. GEM usually accounts for more than 98% of the total pool [16,17], so its concentrations can be considered indicative of total gaseous Hg levels [18]. This form is very stable in the atmosphere where it can persist for 0.5-2 years [19] and undergo long-range transport before being removed through depositions, thus impacting remote areas such as the Arctic [20].…”

Gaseous Elemental Mercury Concentrations along the Northern Gulf of Mexico Using Passive Air Sampling, with a Comparison to Active Sampling

“…Previous studies have shown that coastal sites can be influenced by both polluted air from urban environments and cleaner Gulf of Mexico marine air [17,39]. In our study, GEM concentrations varied GEM levels tend to be higher in the winter due in part to the uptake of Hg by plants during the growing season which generally extends from spring through early fall [5], but also due to shifts in prevailing winds which are generally from the south (arriving from the GoM) in the summer and from the north (over terrestrial areas with point sources) in the winter (Figure A2) [16,17].…”