## 4 Conclusions  
An off-grid air monitoring station was established in a remote and near-pristine location in Ontario's Far North to monitor regional background levels of PM\({}_{2.5}\) and trace elements using a system powered by batteries and recharged with solar and wind power. The shelter was built on a solid permafrost layer approximately 9 feet below the ground level and did not experience any shifting of its position due to the freeze-thaw cycles. The six batteries provided enough power to run air and meteorological instrumentation even in cold winter conditions. However, the batteries were incapable of fully charging after four winters in the field and were replaced as part of the station maintenance. The PQ100 samplers ran well year-round except for a few samples that collected an air volume that was less than the target of 24 m\({}^{3}\). In these instances, the samplers stopped in the middle of a sampling event during the winter, presumably due to less sunlight and consequently less battery power. A power monitor is recommended to better manage the power supply especially during winter months when daytime is short and temperatures are low. A total of 46 air samples and hourly meteorological data were collected from 2015 to 2018. The data collected in 2015-2018 are representative of baseline levels of PM\({}_{2.5}\) and trace elements in this region. These measurements can be used to assess the impacts of  
Figure 7: CPF plots for PM\({}_{2.5}\), As, Se, Pb, Sb, Mn, La, and Ce. In each circular plot, directions centered on the receptor site are sorted into 36 equal arc segments with 10\({}^{\circ}\) each segment, and the solid line represents probabilities of potential sources to the receptor site. The 0\({}^{\circ}\) refers to the north. mining activities on ambient air quality should the proposed development occur. The dominant winds were found to be from the northwest and southwest indicating that the air monitoring station was generally located downwind of the proposed Eagle's Nest mine site and is thus suitable for assessing the potential impacts of the proposed mining activities on regional air quality. PM\({}_{2.5}\) concentrations were generally lower than measurements at AQHI monitoring stations in southern Ontario, suggesting minimal influence of local primary emissions. The maximum 24 h PM\({}_{2.5}\) concentration was 19 \(\upmu\)g/m\({}^{3}\), which was attributable to wildfire emissions in northern Ontario. Levels of trace elements were quite low and only 8 out of the 31 quantified elements were detected in 25% or more of the samples. Concentrations were lower than those observed at stations in southern Ontario during 2015-2018. The monitoring data were further compared against calculated 24 h AAQCs to assess health implications of air pollutants. No target elements were found to exceed these calculated 24 h AAQCs (in ng/m\({}^{3}\)) for the PM\({}_{2.5}\) fraction in any of the air samples. Ambient levels of As, Se, Pb, and Sb were highly correlated, suggesting common emission sources of these elements likely from long-range transport of coal combustion emissions. Similarly, good correlation between Mn and Fe suggests common sources, likely associated with iron and steel industries and coal combustion. The potential sources of PM\({}_{2.5}\) and seven elements appeared fairly similar with potential sources from southwestern and southern directions. No potential sources were identified from the proposed Eagle's Nest mine site. Given little local emission sources in Ontario's Far North, these pollutants are attributable to long-range atmospheric transport from the south. Measurements from 2015 to 2018 showed that the air instruments and meteorological sensors worked well in the harsh environment of Ontario's Far North. Field experience gained over the course of this monitoring campaign can help future air monitoring efforts in other similarly challenging environments.