Tempo-spatial patterns of PM_2.5 measured using a portable particulate monitor around a mine complex in Canada's...

Mining activities in Canada's pristine Arctic (e.g., driving on unpacked roads, blasts, rock grinding, diesel combustion, and garbage incineration) could add local sources of airborne fine particulate matter with a diameter of < 2.5 μm (PM_2.5) to their surrounding area. The increase in PM_2.5 above the background level around a mine represents a potential disturbance to caribou. To quantify the spatial distribution of the elevated PM_2.5, we investigated three different sampling schemes to measure PM_2.5 concentration using a portable monitor. We found that the best sampling scheme was to use the regional background PM_2.5 as the reference and analyze the anomaly of PM_2.5 measured at sites around the mine complex from the background level. The regional background PM_2.5 values were measured at the Daring Lake Tundra Research Station during 2018 and 2019. Our results indicated that the background PM_2.5 was not a low and constant value but varied with rain events, wind direction, and the impacts of forest fire smoke. After excluding periods affected by forest fires smokes, we found the background PM_2.5 was close to 0 μg m^-3 for the first few hours after rain, and then increased logistically with the time after rain (t_ar) to the maximum of 5 (or 10) μg m^-3 when the wind came from the north (or south) of the NW-SE axis. The NW-SE axis in western Canada divides the tundra north with few anthropogenic PM_2.5 sources from the forested south with many PM_2.5 sources from forest fire smokes and human activities. Analyses of PM_2.5 anomaly from the background (i.e., PM_2.5 measured at a site around the mining complex-the background level at the corresponding t_ar and wind direction) revealed that the zone of elevated PM_2.5 around the mine (Z_epm) expanded with t_ar. In the first few hours after rain, PM_2.5 was close to 0 everywhere except within meters of a source (e.g., a truck exhaust) in the downwind direction. During t_ar = 6 to 96 h, Z_epm expanded to 6.3 km in the downwind direction when the wind came from south of the NW-SE axis. A similar result was found in the downwind direction when the wind came from north of the NW-SE axis, with Z_epm = 4.4 km. In the upwind direction, the value of Z_epm was much smaller, being 0.7 km (or 1.0 km) when the wind came from the north (or south) of the NW-SE axis. For the period of t_ar between 96 and 192 hours, Z_epm further expanded to 21.2 km when the wind from the south of the NW-SE axis. The results from this study indicated that this reference paradigm that uses the regional background PM_2.5 as the reference in combination with a portable PM_2.5 monitor worked well for quantifying the tempo-spatial patterns of PM_2.5 at locations in remote and mostly pristine Arctic. However, their effectiveness for other regions needs further investigation.