Ambient air total gaseous mercury concentrations in the vicinity of coal-fired power plants in Alberta, Canada

The Lake Wabamun area, in Alberta, is unique within Canada as there are four coal-fired power plants within a 500 km² area. Continuous monitoring of ambient total gaseous mercury (TGM) concentrations in the Lake Wabamun area was undertaken at two sites, Genesee and Meadows. The data were analyzed in order to characterise the effect of the coal-fired power plants on the regional TGM. Mean concentrations of 1.57 ng/m³ for Genesee and 1.50 ng/m³ for Meadows were comparable to other Canadian sites. Maximum concentrations of 9.50 ng/m³ and 4.43 ng/m³ were comparable to maxima recorded at Canadian sites influenced by anthropogenic sources. The Genesee site was directly affected by the coal-fired power plants with the occurrence of northwest winds, and this was evident by episodes of elevated TGM, NO_x and SO₂ concentrations. NO_x/TGM and SO₂/TGM ratios of 21.71 and 19.98 µg/ng, respectively, were characteristic of the episodic events from the northwest wind direction. AERMOD modeling predicted that coal-fired power plant TGM emissions under normal operating conditions can influence hourly ground-level concentrations by 0.46-1.19 ng/m³_. The effect of changes in coal-fired power plant electricity production on the ambient TGM concentrations was also investigated, and was useful in describing some of the episodes.