Identification of potential regional sources of atmospheric total gaseous mercury in Windsor, Ontario, Canada using hybrid receptor modeling

Abstract

Windsor (Ontario, Canada) experiences trans-boundary air pollution as it is located on the border immediately downwind of industrialized regions of the United States of America. A study was conducted in 2007 to identify the potential regional sources of total gaseous mercury (TGM) and investigate the effects of regional sources and other factors on seasonal variability of TGM concentrations in Windsor. <br><br> TGM concentration was measured at the University of Windsor campus using a Tekran® 2537A Hg vapour analyzer. An annual mean of 2.02±1.63 ng/m<sup>3</sup> was observed in 2007. The average TGM concentration was high in the summer (2.48±2.68 ng/m<sup>3</sup>) and winter (2.17±2.01 ng/m<sup>3</sup>), compared to spring (1.88±0.78 ng/m<sup>3</sup>) and fall (1.76±0.58 ng/m<sup>3</sup>). Hybrid receptor modeling potential source contribution function (PSCF) was used by incorporating 72-h backward trajectories and measurements of TGM in Windsor. The results of PSCF were analyzed in conjunction with the Hg emissions inventory of North America (by state/province) to identify regions affecting Windsor. In addition to annual modeling, seasonal PSCF modeling was also conducted. The potential source region was identified between 24–61° N and 51–143° W. Annual PSCF modeling identified major sources southwest of Windsor, stretching from Ohio to Texas. The emissions inventory also supported the findings, as Hg emissions were high in those regions. Results of seasonal PSCF modeling were analyzed to find the combined effects of regional sources, meteorological conditions, and surface re-emissions, on seasonal variability of Hg concentrations. It was found that the summer and winter highs of atmospheric Hg can be attributed to areas where large numbers of coal fired power plants are located in the USA. Weak atmospheric dispersion due to low winds and high re-emission from surfaces due to higher temperatures also contributed to high concentrations in the summer. In the winter, the atmospheric removal of Hg was slow, but strong winds led to more dispersion, resulting in lower concentrations than the summer. Future studies could use smaller grid sizes and refined emission inventories, for more accurate analysis of source-receptor relationship of atmospheric Hg

Concentration-weighted trajectory approach to identifying potential sources of speciated atmospheric mercury at an urban coastal site in Nova Scotia, Canada

“…Average GOM concentrations in the spring were statistically higher than those in other seasons. The GEM trend at Dartmouth was partly consistent with other urban sites, where higher average GEM concentrations were typically observed in spring or summer (Liu et al, 2010;Xu and Akhtar, 2010;Nair et al, 2012). This was attributed to enhanced GEM emissions from surfaces during warmer months and regional source emissions (e.g.…”

“…This was attributed to enhanced GEM emissions from surfaces during warmer months and regional source emissions (e.g. increased electricity generation) (Liu et al, 2010;Xu and Akhtar, 2010). Seasonal patterns for PBM at Dartmouth were consistent with most of the urban locations in Table 1.…”

“…These observations were typically attributed to major sources of Hg surrounding the urban sites, such as coal-fired power plants and industrial facilities. However, not all urban sites were located near combustion and industrial sources; therefore in these cases, the sources were attributed to regional and long-range transport of Hg emissions and local vehicular emissions and surface emissions (Lynam and Keeler, 2006;Cheng et al, 2009;Xu and Akhtar, 2010).…”

“…In Canada, these measurements have taken place at two urban locations: Toronto and Windsor (Xu and Akhtar, 2010). A common trend among urban sites is the higher average gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and fine particle-bound mercury (PBM) concentrations compared to rural and remote sites (Ebinghaus et al, 2010).…”

“…When the results are plotted on a map, these models illustrate potential source areas affecting a receptor site. There are several variations of TSMs that have been applied to speciated atmospheric Hg studies: Potential Source Contribution Function (PSCF) (Han et al, 2005(Han et al, , 2007Abbott et al, 2008;Choi et al, 2008;Xu and Akhtar, 2010;Fu et al, 2011), Gridded Frequency Distributions (GFD) (Weiss-Penzias et al, 2011;Gustin et al, 2012), Concentration Fields Analysis (Rutter et al, 2009) or Concentration-Weighted Trajectory (CWT), and Residence Time Weighted Concentration (RTWC) (Han et al, 2007). They all involve counting the frequency of back trajectory segment endpoints in grid cells that make up the geographical domain of interest for the receptor site.…”