## 1 Introduction  
The Ring of Fire area is located in Ontario's Far North in the James Bay Lowlands which is dominated by northern peatlands and a globally significant carbon store [1]. Large mineral deposits have been discovered in this near-pristine area including the Black Thor chromite deposit, estimated as at least 220 million tonnes of chromite, and the Eagle's Nest nickel-copper deposit. Both deposits are being considered for further development [2, 3]. It is, however, environmentally and logistically challenging to conduct mining and ore-processing activities in this sensitive ecosystem [4].  
Particulate matter and trace elements can be emitted from mining activities, such as drilling, blasting, hailing, collection, and transportation [5]. Fine particulate matter (PM\({}_{2.5}\)) refers to particles with an aerodynamic diameter less than 2.5 micrometers. PM\({}_{2.5}\) can penetrate deep into the respiratory system due to its small size. Major components of PM\({}_{2.5}\) in southern Ontario are typically nitrate, sulphate, elemental carbon, organic matter, and particle-bound water. Higher nitrate levels are common in cold months whereas sulphate is usually more elevated during warm months [6]. PM\({}_{2.5}\) also contains trace levels of elements [6; 7], which are emitted to the environment naturally or are released from various industrial activities (e.g., mining, smelting, and combustion) [8]. Exposure to PM\({}_{2.5}\) is associated with various health effects, including asthma, cardiovascular and lung disease, and premature death [9; 10; 11; 12; 13; 14]. Some heavy metals are associated with health risks and categorized as human carcinogens [15; 16; 17]. The International Agency for Research on Cancer classified outdoor air pollution and particulate matter as carcinogenic to humans based on evidence of carcinogenicity in humans and experimental animals [18]. Trace elements in PM\({}_{2.5}\) are further subject to atmospheric deposition that can lead to build-up in soils and surface waters. They are also transported over long distances by air from source regions to remote areas due to their persistence in the environment [19].  
PM\({}_{2.5}\) and trace elements are routinely monitored in populated southern Ontario to assess long-term trends and their associations with changing emissions by using continuous and integrated methods [6; 20; 21]. However, no air quality data were available in the Ring of Fire area. Baseline air monitoring is needed to fill the data gap and can be used to assess impacts of potential mining development on ambient levels of PM\({}_{2.5}\) and trace elements, and to help characterize associated emissions. The long-term air monitoring stations usually have direct power supply and are easily accessible to perform routine instrument maintenance. Air instruments for PM\({}_{2.5}\) and trace elements are housed in a temperature-controlled shelter or on a roof-top [6; 20; 21; 22]. However, air monitoring in the near-pristine Far North encountered logistical challenges since there is neither direct power supply nor all-season roads to access the monitoring site. Furthermore, ambient temperatures can drop below \(-30\)\({}^{\circ}\)C in winter months. Lack of the power supply and the harsh environment greatly limited selection of air monitoring instruments to be deployed in the field. The Ring of Fire area is accessible by winter roads during cold months and by helicopter flights, which poses constraints on regular site visits. The main objectives of this study were: (1) to establish an air monitoring platform on peatlands in the Ring of Fire area, (2) to assess field performance of battery-powered air instrumentation in the harsh environment of Ontario's Far North, especially during the colder winter months, (3) to measure and report on baseline levels of PM\({}_{2.5}\) and trace elements downwind of the proposed Eagle's Nest mine site, and (4) to compare air measurements to Ontario's Ambient Air Quality Criteria (AAQC) to determine the potential human health implications.