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Oct 7, 2021 · The majority of Canadians live in parts of the country where air pollution exceeds new guidelines set by the World Health Organization, and this could damage their health, researchers say.
Dec 2, 2022 · London, Ontario is reported as having the best environmental conditions in the country with a median EQI of 70, followed by Guelph, Ontario (68.9). The lowest values belong to Edmonton (42.2) and Calgary (46.6). Halifax finds itself in the middle of the pack with an EQI median of 62.2.
Air pollution is deadly, and people living in cities are most affected. The health risk comes from harmful gases and fine particles in polluted air that penetrate deep into our lungs and pass into our bloodstreams, affecting our respiratory, cardiovascular and other body systems.
- Overview
- Table of contents
- Summary
- 1. Introduction
- 2. Methods
- 3. Results
- 4. Discussion
- 5. Conclusions
- 6. References
- Appendix A. Information on air emissions levels and sources associated with ambient concentrations of PM2.5, ozone and NO2 in Canada
(PDF format, 6.23MB, 56 pages)
Organization: Health Canada or
Published: by authority of the Minister of Health
Cat.: H144-51/2021E-PDF
ISBN: 978-0-660-37331-7
Pub.: 200423
•Summary
•1.0 Introduction
•2.0 Methods
•2.1 Pollutants included in the estimate
•2.2 Estimating population exposures to above-background air pollution
•2.3 Estimating premature deaths and nonfatal outcomes from air pollution
A large body of scientific evidence has accumulated over the past 25 years attributing a wide range of adverse health effects to ambient (outdoor) air pollution exposure. These effects range in severity from respiratory symptoms to the development of disease and premature death. Significant advances in the health and atmospheric sciences over the last two decades have also made it possible to estimate the number of deaths and illnesses associated with air pollution. In Canada and internationally, health impact assessments identify air pollution as one of the largest risk factors for premature death and disability.
In this report, air pollution is defined as pollutants that scientific studies have associated with wide-ranging health effects and to which the population is ubiquitously exposed in the outdoor environment. These pollutants include fine particulate matter (PM2.5), ground-level ozone, and nitrogen dioxide (NO2). This is an update to previous health impacts of air pollution reports published by Health Canada. It relies on data and scientific knowledge, including ambient air pollution exposure estimates and demographic data from 2014 to 2017. The approach for quantitatively estimating the population health impacts of air pollution is well established by international health science organizations. In alignment with established approaches, Health Canada estimated 1) exposures to ambient air pollution across Canada, 2) the associated adverse health impacts in the population and 3) the corresponding economic costs of these health impacts. This analysis accounts for national demographics, including population counts, age profiles and baseline health status. Health impacts are presented nationally, as well as by province and territory (using 2016 population data).
This report considers Canadians’ exposure to above-background levels. Above-background levels correspond to the difference between ambient concentrations and background concentrations. Background concentrations are equivalent to minimum ambient air pollution levels, such as those present in remote areas uninfluenced by human activity. The above-background air pollution is comprised mostly of human-source (anthropogenic) emissions, but it also includes emissions from natural events such as forest fires. Exposure to air pollutants in indoor environments was not considered. The focus on above-background air pollution is relevant to air quality management in Canada because policies and regulations to improve air quality generally target anthropogenic emissions. The national average exposure to above-background air pollution estimates were 4.3 µg/m3 for PM2.5, 7.2 ppb for NO2, 13.2 ppb for annual ozone and 14.4 ppb for summer ozone. These averages are population-weighted to account for the geographic distribution of the Canadian population.
Health Canada estimates that above-background air pollution, including air pollution from human sources in North America, contributes to 15,300 premature deaths per year in Canada. Footnote 1 This includes an estimated 6,600 premature deaths in Ontario, 4,000 in Quebec, 1,900 in British Columbia and 1,400 in Alberta. National morbidity or nonfatal health outcomes include 2.7 million asthma symptom days and 35 million acute respiratory symptom days per year, with the total economic cost of all health impacts attributable to air pollution for the year being $120 billion (2016 CAD). This is equivalent to approximately 6% of Canada’s 2016 real gross domestic product.
The mortality estimates reported in this assessment are based on risk information from epidemiological studies deemed to be the most relevant to Canada. The mortality endpoints include all-cause mortality Footnote 2 associated with long-term exposure to ambient PM2.5, and short-term exposure to NO2 and annual ozone, as well as respiratory mortality associated with long-term exposure to warm-season ozone. All risk information contributing to Health Canada’s mortality estimates was derived from Canadian cohort and time-series studies, with the exception of chronic exposure respiratory mortality associated with ozone that was derived from an American cohort. In the context of this analysis, short-term exposure is related to effects that occur a few days after an elevation in ambient air pollution (i.e. acute health effects), while long-term exposure refers to exposures averaged over the years preceding the development of disease or death (i.e. chronic health effects).
In addition to the effects of changes in air pollution exposure over time, population growth also influences the overall health burden of air pollution, leading to a greater number of exposed individuals and resulting in an overall net increase in premature deaths attributable to air pollution. These variations in population can be standardized by presenting the death rates per 100,000 population. The current estimate of 15,300 premature deaths is equivalent to 42 premature deaths per 100,000 Canadians. Health Canada estimated, in 2017, 14,400 premature deaths per year, and, in 2019, 14,600 premature deaths per year, which were equivalent to 41–42 deaths per 100,000 Canadians. Footnote 3
Air pollution is recognized globally as a major contributor to the development of disease and premature death and represents the largest environmental risk factor to human health (WHO 2016). Exposure to air pollution increases the risk of premature mortality from heart disease, stroke and lung cancer. Footnote 4 The health and atmospheric sciences have advanced significantly in the past two decades, making it possible to estimate the number of deaths and illnesses associated with air pollution. These values are estimated using information from the peer-reviewed scientific literature, which relates population-level pollution exposure (both short-term and long-term) to the risk of adverse health outcomes, including premature death and hospital visits. The quantitative relationship between exposure and increased risk of adverse health outcomes is referred to as the concentration-response function (CRF). Estimates of air pollution-attributable deaths and other adverse health outcomes have been developed globally and for many individual countries, including by Cohen et al. (2017), the Institute for Health Metrics and Evaluation (IHME) and the Health Effects Institute (HEI) (2018), and the World Health Organization (WHO) (2016).
According to the Global Burden of Disease (GBD) project, air pollution is the fifth leading mortality risk in the world and was responsible for 8.7% of deaths globally in 2017 (or 4.9 million premature deaths worldwide) (IHME and HEI 2019). Internationally, Canada is among the top 10 countries with the lowest national PM2.5 exposure levels (IHME and HEI 2019). According to the GBD analyses, air pollution ranks as the 11th largest risk factor overall for premature death and disability in Canada, and is the top environmental risk. Footnote 5
Estimates of air pollution-attributable mortality in Canada have previously been developed by Health Canada (2017, 2019), Stieb et al. (2015), the Canadian Medical Association (2008), and as part of the GBD project. Footnote 6 The previous edition of this report (Health Canada 2019) estimated that 14,600 premature deaths were associated with ambient air pollution exposure in 2015. In this context, air pollution is defined as pollutants that scientific studies have associated with wide-ranging health effects and to which the population is ubiquitously exposed. These pollutants include PM2.5, ground-level ozone, and NO2. While both sulphur dioxide and carbon monoxide are also ubiquitous in Canada and have also been associated with such effects in some studies, they appear to have far less important impact than the three pollutants listed above.
Estimates of air pollution-attributable fatal and nonfatal outcomes are expected to change over time as a result of our improving understanding of the relationship between exposure and risk and the spatial representation of air pollution exposure. For example, new scientific information may support or confirm the inclusion of additional causes of death associated with air pollution. In addition, new air pollution exposure data and modelling tools provide more accurate air pollution level estimates with improved spatial and temporal resolution for all regions of Canada. Changes in population health and demographics, including the aging population, will influence the number of health outcomes attributable to air pollution exposure.
2.1 Pollutants included in the estimate
This analysis of air pollution health impacts in Canada focuses on PM2.5, NO2, and ozone. Emissions from local, regional, national and international sources directly (primary emissions) and indirectly (secondary formation) contribute to the presence of these pollutants in the country’s ambient air. Fuel combustion, including from mobile (e.g. on-road vehicles and off-road equipment) and power generation (e.g. coal or natural gas) sources, directly releases particles and nitrogen oxides (NOx) into the air. In addition, combustion emits a suite of organic and inorganic compounds that contribute to secondary PM2.5 and ozone. Ozone is not emitted directly, but formed from precursors such as NOx and volatile organic compounds (VOCs) via secondary reactions in the atmosphere and reactions with sunlight. Health Canada and other international agencies have concluded that PM2.5, NO2 and ozone cause or are likely to cause premature mortality based on extensive evidence from epidemiological studies (e.g. Health Canada 2013, 2016; US EPA 2019). These three pollutants also account for the majority of population health impacts from air pollution. There is robust scientific evidence of health effects at very low concentrations of these pollutants, and no evidence of an exposure threshold in the population. In other words, any incremental increase in air pollutant concentration is associated with an increased risk of adverse health outcomes. General information on emissions and ambient concentrations of NO2, ozone, and PM2.5 in Canada as well as the associated adverse health effects are presented in Appendix A.
2.2 Estimating population exposures to above-background air pollution
The current analysis estimates the mortality and morbidity outcomes associated with ambient air pollution corresponding to above-background levels. While most of the above-background increment is linked to human source (anthropogenic) emissions originating from North America, natural emissions are also included, notably from wildfires. Health impacts associated with “background” pollutant concentrations (which include emissions from other natural sources and sources beyond North America) were not included. Footnote 7 This measurement of above-background air pollution is relevant to air quality management in Canada, as policies and regulations generally target anthropogenic emissions to improve air quality. High-resolution estimates of ambient concentrations of PM2.5, NO2, and ozone were used to estimate population-level exposures across Canada. These estimates, which are presented graphically in Figures 1–3, were generated using a combination of ground-level measurements, satellite data, geographic and land-use information, as well as computer model simulations. Background concentrations were then subtracted to obtain the exposure data included in this analysis. 2.2.1 Background concentrations of air pollution Background concentrations of PM2.5, NO2 and ozone were estimated in collaboration with Environment and Climate Change Canada (Judek et al. 2004). This complex initiative involved a combination of qualitative (i.e. expert judgment) and quantitative (i.e. data-driven) approaches to evaluate concentration measurements at rural and remote monitoring sites. Background concentrations were estimated using either one of the following methods: The data from rural and remote monitoring sites were separated into sectors of different air mass origin, and the background concentrations were selected as the monthly or annual average concentrations for the sectors containing no major anthropogenic sources; or Many years of rural and remote measurement data were plotted in a time series allowing a qualitative selection of the lowest values that are considered to be the most representative of background air masses. This resulted in annual average background concentrations for NO2 and PM2.5. A set of monthly-average background concentrations were derived for ozone, for which the ambient concentrations have a strongly seasonal cycle. These monthly averages were then combined into summer and annual average concentrations to be consistent with those used to quantify health risks. Regional differences in background concentrations are likely, but for the purposes of this analysis, a single background concentration was applied across Canada for each pollutant. Footnote 8 The estimated background concentrations for Canada are as follows: 1.8 micrograms per cubic metre (µg/m3) for PM2.5 (annual average). 0.15 parts per billion by volume (ppb) for NO2 (annual average). 26 ppb for annual ozone (annual average of daily 1-h maximum) and 28 ppb for summer ozone (May–September average of daily 1-h maximum). 2.2.2 Above-background air pollution To estimate the population health impacts attributable to above background air pollution, it is necessary to calculate the above-background air pollution increment. Air pollution levels are known to vary geographically and can be estimated using a combination of observed and simulated concentrations. Routine ground-level air pollution monitoring in Canada occurs at discrete monitoring stations across the country, which limits the geographic coverage of air pollution exposure estimates that rely solely on direct measurements. For this assessment, we relied on spatially resolved estimates of ambient air pollution levels (including both anthropogenic and natural sources, and non–North American contributions) for PM2.5, NO2 and ozone, produced through a combination of data sources, including ambient monitoring, as described below. In contrast, a single background concentration for each pollutant was developed and was assumed to apply across Canada (as described in the previous section). 2.2.3 Assignment of concentrations to populations Air pollution concentration estimates for NO2, PM2.5 and ozone were generated and mapped to the Canadian population (using the 2011 census, with population counts for 2016). Ambient concentrations were averaged over three years of available data (between 2014 and 2017) to ensure that results were not influenced by any interannual variations in concentrations. Abnormal weather patterns and air pollution events, including wildfires and stay-at-home orders, are possible causes of interannual variations (Griffin et al. 2020; Matz et al. 2020; Zangari et al. 2020). Air pollution concentrations were estimated for up to 293 census divisions (CDs). Footnote 9 Figures 1 to 3 present maps of population-weighted ambient air pollutant concentrations for annual average PM2.5, annual 1-h daily maximum ozone, summer 1-h daily maximum ozone (i.e. May–September), and annual average NO2. The data displayed in these maps represent the estimated distribution of ambient air concentrations from all natural and anthropogenic sources. Canadian background concentrations were then subtracted to estimate exposures to above-background ambient air pollution concentrations. The methods used to estimate air pollutant levels are detailed in the following subsections. 2.2.3.1 Fine particulate matter Annual average PM2.5 concentrations for 2015–2017 were derived from optimal estimation methods combining remote-sensing observations, chemical transport modelling and ground-based observations (van Donkelaar et al. 2015a). Aerosol optical depth (AOD) data were obtained from three satellite instruments: Multi-angle Imaging SpectroRadiometer (MISR), Moderate Resolution Imaging Spectroradiometer (MODIS), and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) (Boys et al. 2014; Crouse et al. 2015; Stieb et al. 2015; van Donkelaar et al. 2010, 2013, 2015a). AOD is a vertically integrated measurement of light extinction in the atmosphere, which is associated with aerosols. Factors such as the vertical distribution and composition of aerosols, as well as humidity and other meteorological conditions, can influence estimates of ground-level PM2.5 concentrations based on AOD measurements. To account for these factors, AOD values can be normalized or adjusted using output from chemical transport models and ground-based observations. For the current assessment, AOD data were combined with information obtained from the Goddard Earth Observing System chemical transport model (GEOS-Chem) and Canada’s National Air Pollution Surveillance (NAPS) network (ground-based air pollutant monitoring) to provide final national estimates of PM2.5 levels (van Donkelaar et al. 2015b). The annual average PM2.5 concentration estimates were generated as a gridded surface with a spatial resolution of approximately 1 km × 1 km. The grid cell values were then converted to a point dataset and merged with a dataset representing postal code areas. The nearest point was assigned to each postal code. The postal code results were then combined with dissemination area (DA) population data to calculate population-weighted concentrations for each CD. Figure 1 shows the distribution of annual average PM2.5 concentrations for the years 2015 to 2017. The national population-weighted average ambient PM2.5 concentration is 6.1 µg/m3 during the period of interest. As expected, higher PM2.5 concentrations are observed in many of the more populous CDs, such as those in the Lower Fraser Valley of British Columbia, the Calgary–Edmonton Corridor in Alberta, and along the Windsor–Quebec City Corridor in Ontario and Quebec (Figure 1). Figure 1. Three-year population-weighted average of daily PM2.5 concentrations across Canadian census divisions – 2015–2017 (includes air pollution from all sources) 2.2.3.2 Ozone Estimates of both the (1) annual ozone average and (2) summer ozone average (May–September) were derived from daily 1-h maximum concentrations for 2014, 2015 and 2017. Data for 2016 were not available owing to operational considerations for the underlying model. These estimates were produced by Environment and Climate Change Canada using objective analysis, an interpolation technique that weighs and combines modelled ozone forecasts with observations of ozone (Robichaud and Ménard 2014; Kalnay 2003). The model led ozone forecast was provided by the Global Environmental Multiscale - Modelling Air quality and Chemistry (GEM-MACH) system, Environment and Climate Change Canada’s operational regional air quality forecast model (e.g. Makar et al. 2018; Moran et al. 2010; Whaley et al. 2018). Ozone measurements were obtained from the Canadian Air and Precipitation Monitoring Network (CAPMoN) and the Canadian NAPS network. In objective analysis, the optimal combination of modelled and observed values improves the coverage and accuracy of air pollution patterns (Robichaud et al. 2016). Objective analysis leads to better estimates of ambient ozone concentrations in areas lacking monitoring data compared to standard interpolation techniques (such as spatial kriging). Estimates for Canada are available for 2014, 2015 and 2017, on a grid point surface with a horizontal resolution of 10 km x 10 km. The grid point estimates were then interpolated to CD polygons (using a normalized conservative approach). All grid points within and bordering CD polygons were included, wholly or partially, to estimate the average ozone concentration values by CD. Figure 2 (top panel) shows the distribution of the annual average of daily 1-h maximum ozone concentrations for the years 2014, 2015 and 2017. The distribution of summer-average daily 1-h maximum ozone is similar (Figure 2–bottom panel). Higher ozone concentrations are observed in the Lower Fraser Valley of British Columbia, in southern Alberta and along the Windsor–Quebec City Corridor, including many of the more populous CDs in Canada. As environmental and meteorological conditions in warmer months promote the formation of ozone, higher concentrations are also observed in the summer: The national population-weighted average ambient concentrations are 39.2 ppb for annual ozone and 42.4 ppb for summer ozone. Figure 2. Three-year population-weighted annual (top panel) and summer (bottom panel) average of the daily 1-h maximum ozone concentrations across Canadian census divisions – 2014, 2015 and 2017 (includes air pollution from all sources) 2.2.3.3 Nitrogen dioxide Annual average NO2 concentrations were estimated using a national land-use regression (LUR) model for 2015–2017 (Larkin and Hystad 2020). The LUR model predictors included three-year annual average NO2 concentrations for 2015, 2016, and 2017 using NO2 vertical column densities (NASA Earth Observations database Footnote 10) from the Ozone Monitoring Instrument (OMI), as well as land use and meteorological descriptors (e.g. Boersma et al. 2011; Hystad et al. 2011; Lamsal et al. 2008). In addition to the OMI data, the model predictors were population density, railways, temperature, industrial use, highways and expressways, and the normalized difference vegetation index (NDVI). The NO2 estimates were developed on a high-resolution grid (30 m) in order to best capture the fine spatial gradients in NO2 concentrations. The LUR model performance was assessed by comparing predicted and observed NO2 concentrations. Observations corresponded with the three-year annual average NO2 data from the NAPS network for 2015, 2016, and 2017 (180 monitoring stations). A coefficient of determination (R2) of 0.68 was reported between the NO2 model results and the corresponding NAPS data (Larkin and Hystad 2020). In this analysis, the 2015–2017 annual average NO2 estimates were derived for dissemination block (DB) centroids (or nearest valid location). Estimates were available for 486,676 DBs (2016 Census). DB estimates ranged from 0 to 20 ppb, with a mean of 5.4 ppb. The DB results were used to calculate population-weighted concentrations for each CD. Figure 3 shows the distribution of annual average NO2 concentrations, averaged over 2015 to 2017. The national population-weighted average ambient concentration is 7.4 ppb for NO2. As is the case for PM2.5 and ozone, higher NO2 concentrations were observed in southwestern British Columbia, around the Calgary–Edmonton Corridor in Alberta, in southern Saskatchewan, and along the Windsor–Quebec City Corridor in Ontario and Quebec. Figure 3. Three-year population-weighted average of daily NO2 concentrations across Canadian census divisions – 2015–2017 (includes air pollution from all sources)
2.3 Estimating premature deaths and nonfatal outcomes from air pollution
This analysis used Health Canada’s Air Quality Benefits Assessment Tool (AQBAT) version 3.0 (Judek et al. 2019; Xu and Stieb Footnote 11) to link population-level above-background air pollution exposure to health outcomes. The AQBAT model estimates the number of premature deaths and other health outcomes associated with specified changes in air pollution concentrations across geographic units (i.e. CDs) in Canada. Outcomes can then be aggregated to provincial, territorial and national health impact estimates, as was done here. Health effect information for the three air pollutants is included in the form of CRFs. A CRF represents the excess health risk for a given endpoint, such as asthma symptoms, chronic bronchitis, and mortality, that follows a unit increase in ambient pollutant concentration. For example, an increase in PM2.5 chronic exposure of 10 µg/m3 leads to a corresponding 10% increase in the risk of premature mortality from nonaccidental causes. A CRF is a statistically derived estimate, from a single study or a meta-analysis of multiple studies. Health endpoints (related to acute or chronic exposure), the associated CRFs and the applicable population group(s) (e.g. age-specific groups) are predefined in AQBAT. In the context of this analysis, short-term exposure contributes to effects that occur within a few days of an increase in ambient air pollution (acute health effects), while long-term exposure refers to exposures averaged over the years preceding the development of disease or death (chronic health effects). Pollutant-specific CRFs for individual adverse health outcomes are drawn from the health science literature and are the consensus selection of a panel of Health Canada experts. They are therefore Health Canada-endorsed values. Table 1 presents the pollutants and their associated health effects considered by this analysis. Previous studies (e.g. Crouse et al. 2012; Judek et al. 2019; Shin et al. 2013; Stieb et al. 2015) contain background information on the CRF estimates used in this analysis (i.e. references to the scientific literature upon which the risk estimates are based) and the analysis undertaken to produce the estimates within AQBAT. This information is also summarized in Appendix B. Health outcomes were considered to have no threshold for effect (i.e. effects were assumed to occur at all levels of exposure), which is consistent with Health Canada’s conclusions upon evaluation of the overall literature on each of these pollutants (Health Canada 2013, 2016).
Table 5 presents the health impact and economic value results for mortality endpoints associated with PM2.5, ozone and NO2 air pollution for national, provincial and territorial geographies. Metrics in Table 5 include the count of incidences and normalized values per 100,000 population. The latter metric allows for comparisons of health impact estimates among geographic regions of different population sizes. All results represent the health impacts attributable to above-background concentrations, as outlined in the Methods section. The Canadian values presented herein have not previously been published.
Overall, the total mortality attributable to above-background air pollution in Canada was estimated to be 15,300 premature deaths per year, based on population data for 2016 and air pollutant concentrations from 2014 to 2017. Footnote 16 More specifically, the following population health impacts of PM2.5, ozone and NO2 were estimated: Footnote 17
•Chronic exposure to PM2.5 air pollution contributed to 8.0% of all-cause nonaccidental mortality among Canadians over 25 years of age, equivalent to 10,000 deaths per year or 27 deaths per 100,000 population.
•Acute exposure to NO2 air pollution contributed to 0.9% of all-cause nonaccidental mortality among Canadians of all ages, equivalent to 1,300 deaths per year or 4 deaths per 100,000 population.
•Acute exposure to ozone was associated with 2.7% of all-cause nonaccidental mortality among Canadians of all ages, equivalent to 2,800 deaths per year or 8 deaths per 100,000 population. This estimate was derived using the annual average of daily 1-h maximum ozone concentrations.
•Chronic exposure to ozone was associated with 10% of respiratory-related mortality among Canadians over 30 years of age, equivalent to 1,300 deaths per year or 4 deaths per 100,000 population. This estimate was derived using the summer average of daily 1-h maximum ozone concentrations.
Health Canada estimates that 15,300 deaths per year are attributable to ambient air pollution in Canada, corresponding to 42 deaths per 100,000 population in 2016. The total monetary value of health outcomes associated with air pollution is approximately $120 billion per year (2016 CAD), a figure equivalent to 6% of Canada’s total real gross domestic product in 2016. Footnote 18 These estimates reflect the contribution from human sources of emissions in North America to Canada’s ambient concentrations of NO2, ozone, and PM2.5, as well as contributions from irregular natural events such as forest fires. In this analysis, air pollution data from 2015 to 2017 were used for NO2 and PM2.5, and from 2014, 2015 and 2017 for ozone. Uniform Canadian background concentrations were subtracted from these three-year average exposure surfaces to estimate the above‑background component of ambient air pollution. This approach was taken because this component, which includes anthropogenic emissions, is generally the subject of air quality management measures. Although Canada’s air pollution levels are low compared to those of other developed nations, Footnote 19 recent Canadian studies indicate that air pollution increases the risk of mortality even at low ambient concentrations (Crouse et al. 2015; Pinault et. al. 2017; Pappin et al. 2019).
The provincial results (Table 5) indicate that Ontario and Quebec see the heaviest health impacts from air pollution, both in terms of mortality count and premature deaths per 100,000 population. This is not unexpected, as approximately 63% of the total Canadian population resides in these two provinces. Further, some of the highest air pollution levels in Canada are found in the southern regions of Ontario and Quebec, which include the highly populated and industrialized Windsor-Quebec City Corridor (encompassing the Greater Toronto and Hamilton Area and Greater Montreal). On the CD level (Tables D1 to D3, Appendix D), results show that higher rates of premature deaths are not correlated solely with higher population; they reflect a combination of environmental factors, age distribution and demographic characteristics, including higher pollution levels and baseline incidence rates. For example, an analysis of health impacts associated with PM2.5 from wildfire smoke in Canada (Matz et al. 2020) indicated that between 2013 and 2018, the 10 CDs with the greatest average wildfire-PM2.5 exposures (45–70% of the total exposure to PM2.5) were all located in British Columbia. Five of those CDs were identified in Table D2 (CDs with the highest rates of premature death per 100,000). Wildfire activity was also common in Alberta, Saskatchewan and Manitoba in 2014, 2015 and 2017 (Matz et al. 2020). In addition, baseline incidence rates integrate various health and demographic variables, notably age distribution. Generally, CDs with older populations will have higher baseline incidence rates and consequently will be associated with higher rates of health outcomes for a given air pollution increment. Notwithstanding the exact causes used for calculating baseline incidence rates across all Canadian CDs, it was observed that several of the CDs with the highest premature death rates are associated with relatively elevated baseline incidence rates (Table D2, Appendix D). Thus, in a given CD, higher rates of health outcomes per 100,000 population represents the integration of several factors that influence the risks associated with exposure to air pollution.
Compared to previous analyses by Health Canada (see Table 7), the mortality health burden of air pollution in Canada for 2016 represents a slight increase in absolute terms: 14,400 in 2011 and 14,600 in 2015 (Health Canada 2017, 2019). The change in the number of premature deaths between analyses should be interpreted in consideration of: 1) estimates of exposure to air pollution across Canada; 2) estimates of the risk of health effects from exposure to air pollutants; and 3) demographic data, including population counts, age profiles and baseline health status. As presented in Table 7, the population-weighted average exposures to air pollution (above-background) in this analysis generally decreased from the previous reports for PM2.5 and summer ozone, whereas a slight increase was estimated for annual ozone. Although the national average estimates are comparable, regional variability can also influence the results. There was an estimated 1.8 ppb‑increase in NO2 exposure since the last analysis.
The variation in NO2 exposure estimates is possibly related in part to modifications in the LUR modelling since the 2014–2016 analysis (Health Canada 2019). Overall, the predictability of the 2014-2016 model reached an R2 of 0.73, compared to 0.68 for the 2015–2017 version. Two important changes include an update to the remote-sensing data Footnote 20 and the use of monitoring data from a near-road monitoring site. Notably, the new model integrates data from a new NAPS station located in downtown Vancouver (station 100141) that were characterized by higher NO2 concentrations than those measured at other monitoring stations. A mean annual average of 22.0 ppb was recorded at this station, over 3 ppb higher than the station with the next highest average (18.7 ppb), also located in downtown Vancouver, and more than 6 ppb higher than the stations with the highest concentrations in other provinces. The inclusion of locations with higher levels of air pollution increased model error. Footnote 21 However, this also increased model generalizability by capturing a unique combination of dense emission sources that are sparsely represented in the NAPS air monitoring network. Thus, while variations in air pollution exposure estimates across analyses can effectively reflect increases or decreases in ambient concentrations, methodological modifications also contribute to variability over time. The recent changes in LUR modelling for NO2 are considered incremental and necessary improvements.
Air pollution is recognized globally as a leading risk factor for premature mortality based on an established database of international epidemiological studies and toxicological investigations. Comprehensive risk assessments performed by Health Canada (2013, 2016) have concluded that, based on extensive research and assessment, exposures to PM2.5, NO2, and ozone have been found to exert the largest population health impacts in Canada.
The current analysis provides estimates of mortality, morbidity and economic costs associated with the above‑background component of ambient air pollutant levels in Canada, which corresponds to air pollution that is targeted by air quality management measures. Health Canada estimates that in 2016, 15,300 premature deaths in Canada could be attributed to air pollution from PM2.5, NO2, and ozone. Nonfatal health outcomes attributable to air pollution include 35 million acute respiratory symptoms days, 2.7 million asthma symptom days and 8,100 emergency room visits. The total economic value of adverse air pollution health impacts is estimated to be $120 billion per year (2016 CAD), equivalent to 6% of total real gross domestic product in 2016. Although air pollution affects the health of Canadians in all regions of the country, the largest impacts are seen in the most populous provinces and those with the largest sources of emissions: Ontario, Quebec, British Columbia and Alberta.
While all three pollutants considered here exert impacts, exposure to PM2.5 represents the majority of the estimated mortality burden (65%), with ozone and NO2 accounting for 26% and 8%, respectively. Regarding nonfatal outcomes, both ozone and PM2.5 are associated with health impacts. This is not the case for NO2 because, while considered to be causally associated with several important respiratory effects, there are currently no CRFs in AQBAT for NO2 and morbidity outcomes.
This estimate of 15,300 deaths per year is equivalent to 42 per 100,000 Canadians and is consistent with previous analyses. The higher number of exposed individuals in 2016 compared to previous years of analysis (owing to population increase) leads to an overall higher mortality count. It is estimated that Canadians are currently exposed, on average, to lower air pollution levels for PM2.5 and summer ozone compared to exposure periods that informed previous analyses. In contrast, this assessment uses overall higher concentrations for annual ozone, while NO2 exposure estimates do not suggest any clear directional change. The normalized value per 100,000 population provides a more objective picture of the health burden and suggests that per capita air pollution-related health risks in Canada have remained consistent over the last decade. While Canadians benefit from relatively good air quality, air pollution continues to have impacts on population health.
The data and methods (e.g. background concentrations, CRFs) used in the current analysis, the most comprehensive analysis available, incorporate the most up-to-date science, data and knowledge on the health effects of air pollution in Canada compared with previous Canadian estimates. Nonetheless, evidence suggests that air pollution may be associated with additional adverse health outcomes that were not considered here. Further, there are air pollutants other than NO2, PM2.5 and ozone that are responsible for adverse health effects. As a result, the quantitative estimates of population health outcomes in this analysis are assumed to underestimate the adverse health impacts of air pollution in Canada.
Changes in health impact estimates are to be expected following each update by Health Canada. Variations or discrepancies between estimates may occur owing to changes in data or methods to assess population exposure to air pollutants, changes in concentration-response relationships, changes in the baseline rates of adverse outcomes in Canada, or changes in population demographics. AQBAT is periodically updated as new evidence is evaluated for inclusion in the model. For example, recent studies have reported a supralinear CRF between exposure to ambient PM2.5 and premature mortality, which would increase count estimates for Canada if it were included in AQBAT for health burden analyses. Evaluation of the relative risks and CRFs at low levels of air pollution, which is particularly relevant for Canada, is also an active area of research (Shaffer et al. 2019). Sensitivity analyses, such as the one discussed above, were conducted to explore the influence of different factors. Finally, there is the possibility of re-estimating the health impacts for years included in Health Canada analyses to ensure that estimates are based on internally consistent methods and data.
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Extensive scientific studies indicate that there are significant health and environmental effects associated with exposure to the air pollutants considered in the current assessment, namely fine particulate matter (PM2.5), ground-level ozone, and nitrogen dioxide (NO2). These pollutants are notably responsible for the formation of smog. This append...
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