## 3 Results and Discussion  
The RM Young wind monitor was in operation from June 2015 to 2018 to measure hourly wind speed and wind direction. By removing calm winds (i.e., wind speeds of 1 m/s or less), wind roses at the air station showed that the predominant winds were from north/south in spring (Figure 2A), north/southwest in summer (Figure 2B), and northwest/southwest in fall (Figure 2C) and winter (Figure 2D). When winds came from the northwest, the air monitoring station was downwind of the proposed Eagle's Nest mine site (Figure 1); therefore, long-term air monitoring at this location could shed light on the impacts of the proposed mining activities on ambient levels of air pollutants and the characteristics of air-related emissions. As indicated earlier, the RM Young and Vaisala WXT 520 instruments were co-located from September 2016 to February 2018 to test and compare their suitability for remote deployments. The concurrent measurements indicated nearly identical wind directions, i.e., mostly originating from the northwest and southwest directions (Figure 2E,F). Both instruments worked well in cold temperatures except that the Vaisala device recorded a few hours of \"0\" values for wind speed and direction when temperatures were close to the freezing point or a few degrees below it. It is believed that these abnormal readings were likely related to freezing raining and/or ice accumulated on the top of the Vaisala device. Measurements of hourly temperature and relative humidity were conducted concurrently using the Met One and Vaisala WXT520 instruments. Data comparison showed that temperatures were fairly comparable between the two instruments and linearly correlated (slope 0.98, intercept \(-\)1.1, and R\({}^{2}\) 0.99). However, the Met One device recorded temperatures a few degrees higher than the Vaisala sensor on a few occasions. Comparison to the meteorological measurements collected by Environment and Climate Change Canada at Lansdowne House (52\({}^{\circ}\)11'44'' N 87\({}^{\circ}\)56'3'' W) suggests that temperatures were overestimated by the Met One device during those occasional events. Measurements from the Vaisala instrument showed that ambient temperatures ranged from \(-\)38 to 31 \({}^{\circ}\)C from September 2016 to February 2018. The low temperatures provided a good opportunity to test the off-grid air monitoring equipment. Overall, all meteorological instruments deployed at the air monitoring station worked well in collecting hourly data even in cold temperatures. Similarly, RH measurements by the two instruments were comparable and linearly correlated (slope 1.0, intercept 2.6, and R\({}^{2}\) 0.97). Since there are limited meteorological measurements in this remote location, concurrent measurements using different instruments are valuable to validate the data and evaluate the field performance of these instruments. A total of 46 air samples collected in 2015-2018 were analyzed for PM\({}_{2.5}\) mass and trace elements. Table 1 summarizes statistics for 24 h concentrations of PM\({}_{2.5}\) and eight individual trace elements (Mn, Fe, As, Se, Sb, La, Ce, and Pb). A complete list for all target elements and concentrations in individual samples can be found in Table S1 of the Supplementary Materials. PM\({}_{2.5}\) was found above the MDL in 63% of the samples, ranging from 0.75 to 19 \(\mathrm{\SIUnitSymbolMicro m}\)/\(\mathrm{m}^{3}\), with an average of 3.0 \(\mathrm{\SIUnitSymbolMicro g}\)/\(\mathrm{m}^{3}\) and a median of 2.2 \(\mathrm{\SIUnitSymbolMicro g}\)/\(\mathrm{m}^{3}\). PM\({}_{2.5}\) was monitored hourly at the ministry's Air Quality Health Index (AQHI) air monitoring stations in southern Ontario that include both urban and rural locations [34]. The average PM\({}_{2.5}\) concentration for samples collected at the Ring of Fire station was lower than those observed at the AQHI stations in southern Ontario (Figure 3). PM\({}_{2.5}\) measurements generally reflected regional background levels in this near-pristine area with fewer contributions from primary emissions.