Ambient air mercury species (TGM, RGM, GEM) concentration study during mid-winter～mid-spring season at a traffic site
Abstract
The main purpose of this study was to monitor ambient air mercury species (TGM, RGM, GEM) of Hung-Kuang traffic area at sampling site during mid-winter～mid-spring season. In addition, four-stage gold amalgamation and denuder samplers were used to collect the ambient air mercury species concentrations, respectively. Moreover, cold-vapor atomic fluorescence spectrometry (CVAFS) was directly used to detect the mercury TGM and RGM concentrations in this study.
The result indicated that: 1). The average ratio for RGM concentrations out of the total gaseous mercury concentration was about 1.65% at the traffic sampling site. 2) The average TGM concentration values obtained in this study were 6630 (pg/m3 ) which is second to China average 9800 (pg/m3 ) when compared with the other countries during year 2010～2013. In addition, Canada showed the average lowest RGM concentrations when Compared the other world areas during year of 2014～2015. The average RGM concentrations ratios for this study (average 91.8 pg/m3) to Canada were about 73.4 during years of 2014～2015. 3) The results indicated that the correlation coefficients among total gaseous mercury (TGM), reaction gaseous mercury (RGM), gaseous element mercury GEM and meteorological conditions such as temperature and wind speed were low correlated related during mid-winter～mid-spring season at this traffic sampling site. 4) Statistical method (MannWhitney U statistical) results revealed that there were significant differences in the mean concentrations values for the ambient air TGM, RGM and TGM were the Hung-Kuang sampling periods at this traffic sampling site
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Introduction
Mercury (Hg) is a trace element distributed throughout the earth's atmosphere, biosphere, and geosphere [1, 2].
Atmospheric Hg consists of three different physical and chemical forms, including gaseous elemental Hg (GEM), reactive gaseous Hg (RGM), and particulate Hg (Hgp) [3].Atmospheric mercury speciation is very important in the determination of the mercury atmospheric residence time. Atmospheric mercury species can be transformed back and forth between two oxidation states (elemental and divalent) [4] and elemental mercury is believed to have a longer residence time of about 1 year [5] compared to the divalent mercury (several hours to several weeks).
Recent studies reported RGM may represent 1–3% of total gaseous Hg (TGM) at rural continental sites [6,7, 8]. Because RGM is highly reactive and rapidly scavenged by moist particles and surfaces, it can fall off quickly with distance from their primary sources (e.g., incinerators, non-metal smelters and power plants) [9].RGM concentrations are likely to be highly variable and related to point sources, meteorological conditions and oxidant levels in the air [10].
The dominant form of mercury in the atmosphere is identified as a gaseous elemental mercury (GEM: e.g., 98%) that is characterized by high stability, low solubility, high volatility, etc. [11]. Gaseous element mercury (GEM) collection and analysis is quite not easy. Including some potential oxidants include HO, O3, HO2, N2O5, O (1D and 3 P), NO2, Cl2, and Br2[12, 13].
Mercury in ocean waters is present as elemental mercury (Hg0), monomethyl mercury (MeHg), dimethyl mercury (Me2Hg), aqueous divalent mercury (Hg II), colloidal mercury, and particulate mercury [14]. Among Hg(p) is associated with airborne particles, such as dust, soot, sea-salt aerosols, ice crystal or is likely produced by adsorption of RGM species (eg, HgCl2) onto atmospheric particles [15].
Conclusion
The major conclusions for this study are as follows:
1) The average ratio for RGM concentrations out of the total gaseous mercury concentration was about 1.65% at the traffic sampling site.
2) The average TGM concentration values obtained in this study were 6630 (pg/m3 ) which is second to China average 9800 (pg/m3 ) when compared with the other countries during year 2010～2013. In addition, Canada showed the average lowest RGM concentrations when Compared the other world areas during year of 2014～2015. The average RGM concentrations ratios for this study (average 91.8 pg/m3) to Canada were about 73.4 during years of 2014～2015.
3) The results indicated that the correlation coefficients among total gaseous mercury (TGM), reaction gaseous mercury (RGM), gaseous element mercury GEM and meteorological conditions such as temperature and wind speed were low correlated related during mid-winter～mid-spring season at this traffic sampling site.
4) Statistical method (Mann-Whitney U statistical) results revealed that there were significant differences in the mean concentrations values for the ambient air TGM, RGM and TGM were the Hung-Kuang sampling periods at this traffic sampling site.