Combustion of fossil fuels and biofuels during energy intensive production processes emits pollutants into the atmosphere [1], which threatens human and ecological health ^[2][3][4][5][2,3,4,5]. However, atmospheric emissions from industrial facilities were once considered a symbol of economic growth, and their effects were not considered harmful until late in the last century [6]. In recent decades, stringent standards were developed around the world to protect human and environmental health ^[7][8][7,8]. In 1970, the Clean Air Act was established in the United States due to growing concerns over air pollution impacts. Even though current legislation in the United States has saved millions of lives, many premature deaths still occur because of breathing polluted air, principally in marginalized sectors such as poor Black or Latino communities [9]. In Canada, the Canadian Environmental Protection Act, 1999 provided legislative authority to protect human and environmental health but was highly criticized for its lack of scientific basis and is currently being amended ^[10][11][12][10,11,12]. In 2006, the Canadian government published a Notice of Intent to regulate air emissions, and one year later, the Clean Air Regulatory Agenda was published to establish a framework on emissions reduction targets and enforceable regulations [13].

In Canada, all companies and organizations that emit certain substances into air, water or land and meet specific threshold requirements must report annual emissions to the federal National Pollutant Release Inventory (NPRI) ^[14][15][14,15]. The NPRI is a registry of annual estimations of emissions and disposal to the environment and was created with the purpose of making pollution data accessible to the Canadian public ^[14][16][14,16]. Due to the threat that some of the releases may pose to human and environmental health, this information was then published on the Environment and Climate Change Canada (ECCC) website [17]. The creation of the NPRI program resulted in a decrease in overall emissions ^[15][18][15,18], although the toxicity of the releases did not decrease [15]. The decrease in overall emissions may have been a direct result of increased public awareness and public pressure, which is the intent of the NPRI program. However, there may have been other reasons, such as improvements in equipment and technology or improvements in industry practices and activities. ECCC requires that releases above reporting thresholds, shown in Table 1 for the period 2020 to 2021, must be reported to the NPRI program [19]. These thresholds are the lower limit trigger for reporting annual emissions; however, there are no regulations for exceedances.

Desirable concentrations of ambient air pollutants, including fine particles (PM_2.5), ozone (O₃), sulphur dioxide (SO₂), and nitrogen dioxide (NO₂), are specified in the Canadian Ambient Air Quality Standards (CAAQS), a national guideline that considers an averaging period to report the concentration of the pollutant in µg/m³ or ppb [20], not compatible with the units reported by NPRI. While there are few onstudies comparing thresholds in units of tonnes per year, onea recent study relates 10-year NPRI industrial air emissions to childhood-onset asthma in Quebec characterizing ‘major emitters’ those industries, for which its PM_2.5 or SO₂ annual emissions exceeded 100 tonnes [5]. Emissions reported through the NPRI program and science-based estimation tools are combined to generate the Air Pollutant Emission Inventory (APEI), which reports air emissions for 17 pollutants since 1990 ^[21][22][21,22]. ECCC recommended thresholds for annual releases (in tonnes) only for total particulate matter (TPM) and SO₂ in the Code of Practice for the Management of Air Emissions from Pulp and Paper Facilities (CPMAEPPF) [23]. These limits are divided into two categories for both pollutants depending on the processes occurring in the facilities (chemical or mechanical) and should be calculated by considering the annual production of each mill. For chemical facilities, emission limits are 2 kg and 4 kg/tonne of production for TPM and SO₂, respectively; for mechanical facilities, those emission limits are 0.5 kg and 1.5 kg/tonne of production for TPM and SO₂, respectively.

Currently, mixtures of air pollutants are considered a management challenge due to the interaction between the chemical and physical components of substances that can increase potential toxicity of emissions ^[6][24][6,24]. While air pollutants exist naturally in the atmosphere from wildfires, volcanic eruptions and biological decomposition, these acid and particulate emissions are relatively small quantities on average and rarely pose threats to human or ecological health ^[4][25][4,25]. Anthropogenic emissions, mainly from industrial activities and fossil fuel combustion, produce the majority of hazardous air pollutants ^{[2][6][24][25][26][27]}[2,6,24,25,26,27]. Pulp and paper (P&P) industries emit large amounts of atmospheric pollutants and greenhouse gases ^[1][28][1,28], although there are few onstudies that quantify the spectrum of emissions [29]. Numerous studies have been conducted on water pollution impacts from wastewater effluent due to P&P mills ^{[8][30][31][32][33][34][35]}[8,30,31,32,33,34,35], but there have been comparatively few onstudies to evaluate the contribution of the industry to the concentrations of hazardous air emissions [36]. Air pollution from P&P mills is mainly caused by the production of various volatile sulfur compounds (from sulfite pulping process), odour emissions (from reduced sulfur), SO₂, and nitrogen oxides (NO_x) ^[37][38][37,38]. Stack emissions can also contain carbon monoxide (CO) [24]. Biomass combustion can increase the emissions of particulate matter (PM) and of gaseous and semi volatile organic compounds (VOCs) ^[24][29][24,29]. Exposure to these pollutants can affect human health, causing cancer or lung diseases ^[9][39][40][9,39,40], and may result in depression or psychological problems [2]. Exposure to particulates is associated with an increased risk of mortality from stroke, heart, or pulmonary disease, among others ^[6][41][42][6,41,42]. One method of reducing human health and environmental impacts of air pollutants is via continuous atmospheric monitoring of pollutant concentrations. Modeling exposures to these concentrations supports epidemiological onstudies to evaluate health risks and the development of management strategies and relevant health interventions ^[15][18][15,18].

In Canada, there are currently 102 pulp, paper, board, and/or tissue mills in operation or which have been temporarily closed [43]. However, few studies have been quantified their compliance with emission standardss based on our literature review. One of the most controversial mills in Atlantic Canada is the Northern Pulp mill in Pictou, Nova Scotia (NS), where locals have long been concerned about health issues and unpleasant odours [44]. While managers of the facility report the best practices with respect to regulatory compliance [45], environmental monitoring revealed emission exceedances and locals remain concerned about impacts to human health ^{[29][46][47][48][49][50]}[29,46,47,48,49,50]. Currently, Nova Scotia does not legislate requirements for emitters to assess human health risks from emissions [50]. Hoffman et al. (2017) also revealed that sediment and water samples, specifically dioxins and furans and metals, from Boat Harbour (a tidal estuary designed to receive wastewater effluent from the mill) were above both the Canadian Sediment Quality Guidelines and Canadian Water Quality Guidelines [50]. However, ambient air pollution concentrations in nearby communities were below the Canadian Council of Minister of the Environment guideline limits. Hoffman et al. [49] found discordance between levels of pollution reported by the mill on NPRI, identifying Total Reduced Sulfur (TRS) to be three times higher in comparison to other Canadian Kraft mills, revealing that the main pollutants from the NP mill were sulfur odours and PM.

The current limitations of air pollution monitoring (for example.g., the NPRI is a self-reported estimated inventory) and the absence of upper air emissions thresholds entangles the identification of harmful releases into the environment. It wasThis study, focused on the air emissions from the P&P industry in Atlantic Canada, compares annual releases among different facilities, identifies the main limitations of the existent reporting tools, and recommends how to improve environmental and human protection regarding air quality. The analysis includes air emissions by nine pulp and/or paper mills for 17 years using publicly available data from NPRI [51] and for 30 years using data from the APEI inventory. The seven pollutants studied were CO, NO_x, TPM, PM_2.5, PM₁₀, SO₂, and VOCs, as these air pollutants are widely reported by industrial facilities as mandated by ECCC for the NPRI inventory and are known to increase risk to human health ^[14][17][14,17].