Tempo-spatial patterns of PM 2.5 measured using a portable particulate monitor around a mine complex in Canada’s Arctic

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.