Impact of Closing Canada’s Largest Point-Source of Mercury Emissions on Local Atmospheric Mercury Concentrations

Abstract

The Flin Flon, Manitoba copper smelter was Canada's largest point source of mercury emissions until its closure in 2010 after ~80 years of operation. The objective of this study was to understand the variables controlling the local ground-level air mercury concentrations before and after this major point source reduction. Total gaseous mercury (TGM) in air, mercury in precipitation, and other ancillary meteorological and air quality parameters were measured pre- and postsmelter closure, and mercury speciation measurements in air were collected postclosure. The results showed that TGM was significantly elevated during the time period when the smelter operated (4.1 ± 3.7 ng m(-3)), decreased only 20% during the year following its closure, and remained ~2-fold above background levels. Similar trends were observed for mercury concentrations in precipitation. Several lines of evidence indicated that while smelter stack emissions would occasionally mix down to the surface resulting in large spikes in TGM concentrations (up to 61 ng m(-3)), the largest contributor to elevated TGM concentrations before and after smelter closure was from surface-air fluxes from mercury-enriched soils and/or tailings. These findings highlight the ability of legacy mercury, deposited to local landscapes over decades from industrial activities, to significantly affect local air concentrations via emissions/re-emissions.

A Survey of Mercury in Air and Precipitation across Canada: Patterns and Trends

“…Therefore, it is expected that TGM concentrations will be fairly uniform at background sites that are far from emission sources, except at sites where other atmospheric processes dominate [9]. The mean TGM concentration of 3.75 ng·m observed at Flin Flon, MB, is a result of local emissions [19]. Overall, TGM concentrations and distributions at these Canadian sites are similar to previously reported data [8,9] where available, with small decreases at some sites observed over the long term (discussed further in Section 2.4).…”

“…While the latter two sites began measurements in the 1990s, the other three cover more recent periods and the lower concentrations may be partially due to decreases in TGM since the 1990s [25,26]. The highest TGM levels by far were observed at Flin Flon, due to local emissions from the copper smelter which was the largest point source of Hg in Canada before closure [19]. The sites that show the most variable TGM concentrations include Alert and Kuujjuarapik, which both experience episodes of rapid conversion of GEM to RGM and/or TPM 2.5 in the spring, known as atmospheric mercury depletion events (AMDEs) [27].…”

“…The atmospheric data are reported as TGM when measured by a Tekran 2537 instrument alone, and GEM, RGM and TPM 2.5 when using the Tekran 2537/1130/1135 system. These data incorporate and update previous measurements reported for some sites [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] and include speciated Hg measurements at several newer sites for the first time. The data were collected and analyzed as part of a Canadian mercury science assessment [23].…”

Total Gaseous Mercury Concentration Measurements at Fort McMurray, Alberta, Canada

“…Principal component analysis (PCA) was performed to identify correlations between parameters and serves as a means for reducing the number of parameters in the dataset into a handful of important factors. PCA was similarly applied in previous work where TGM concentrations were measured alongside a variety of ancillary variables to quantify relationships within the dataset and identify common factors that may influence TGM concentrations [19]. Three data subsets were established in order to better understand the factors affecting TGM and other air quality and meteorological parameters.…”

“…Most of these variables were chosen due to the fact they were measured at Patricia McInnes station. Solar radiation, snow depth, and RH measured at nearby stations were included due to associations with TGM concentration noted in previous work [19]; CO was included as a forest fire tracer as noted below. The data source of each parameter, as listed in Table 6, provides corresponding details on instrumentation; all public data has been quality controlled by the respective operator and provided as hourly averages from continuous instrumentation.…”