Characterization of air quality and sources of fine particulate matter (PM2.5) in the City of Calgary, Canada
Graphical abstract
Introduction
There has been growing awareness and public health concerns about the state of air quality in urban areas. Urban air pollution is generally caused by a wide variety of emission sources including traffic, industry, commercial/residential fuel combustion and is comprised of a complex mixture of gaseous and particulate air contaminants such as nitrogen dioxide (NO2), sulfur dioxide (SO2), fine particulate matter (PM2.5), and ground-level ozone (O3). Epidemiological studies suggest potential associations between short- and long-term exposure to criteria air pollutants and increased morbidity, mortality and hospital admissions for cardiovascular and pulmonary diseases, stroke, as well as decreased life expectancy (Burnett et al., 1999, Burnett et al., 2004, Ruidavets et al., 2005, Pope et al., 2014, Weichenthal et al., 2014, Zanobetti et al., 2014). High concentrations of these pollutants can also contribute to acid deposition, photochemical smog and reduced atmospheric visibility (Cooper and Alley, 2002, Cheung et al., 2005). This has led the Canadian Council of Ministers of the Environment (CCME) to the establishment of health-based air quality standards i.e., Canadian Ambient Air Quality Standards (CAAQS) as a driver for air quality management across the country with an objective to guide work towards better understanding and, where necessary, controlling air emissions in populated urban areas. The new CAAQS for PM2.5 for the year 2015 (annual: 10 μg/m3, 24 h: 28 μg/m3) and 2020 (annual: 8.8 μg/m3, 24 h: 27 μg/m3) (CCME, 2012) replaced the former 24 h Canada-Wide Standard (CWS) of 30 μg/m3 established in 2000 (CCME, 2000).
The City of Calgary is the largest urban area and most populous city (area 825 km2, population 1,246,337, Municipal census, 2017) in the oil and natural gas-rich province of Alberta and third-largest municipality in Canada (Statistics Canada, 2016). It is located about 300 km south of Alberta's capital Edmonton in a valley at the foothills approximately 80 km east of the front ranges of the Canadian Rockies. The city anchors the south end of the Calgary-Edmonton Corridor, which is home to 2.7 million people. Alberta has well-established conventional oil and gas extraction, refining and upgrading activities in addition to unconventional oil sands development in the northeast area of the province. Calgary is located within the southern edge of oil and gas extraction activities (Supplemental Information-SI, Fig. S1a). Because of its diversified economy including oil and gas, film and television industries, transportation and logistics, technology, manufacturing, retail, and tourism sectors, Calgary plays a key role in supporting economic growth of Alberta and Canada.
Evaluation of long-term air monitoring data and characterization of ambient PM2.5 can aid in improving the understanding of the state of air quality and sources of particle pollution in urban areas. In our recent study (Bari and Kindzierski, 2016a), we observed more than 40 (80) exceedances of the 24 h PM2.5 CWS of 30 μg/m3 (1 h Alberta Ambient Air Quality Guideline of 80 μg/m3), respectively over a 17-year period (1998–2014) in Calgary. In addition, the highest 3-year average (2010–2012) of 24 h concentrations was recorded in downtown Calgary among Canadian urban areas. In another study conducted for the time period 2010–2012 in six Alberta airsheds including South Saskatchewan Air Zone where Calgary is located (Fig. S1b), the Government of Alberta (Alberta Environment and Parks-AEP, 2015) reported that air monitoring stations at Calgary central and Calgary northwest had annual PM2.5 metric values of 7.5 μg/m3 (in 2013) and 8.5 μg/m3 (3-year average). The study assigned Calgary to an orange management level for PM2.5 based on four-color coded air quality management thresholds for 2015 (Table S1), suggesting that PM2.5 concentrations were approaching the new CAAQS and proactive planning and/or action may be needed to prevent exceedances. It was therefore of interest to undertake an exploratory study to evaluate PM2.5 levels and to identify different emission sources that affect PM2.5 levels in Calgary.
In general, 24 h PM2.5 chemical speciation data has been widely used in multivariate receptor models to identify and distinguish different emission sources in urban areas. Due to cost, however many monitoring organizations do not have the capabilities and financial resources to routinely monitor for PM2.5 chemical species. Environment and Climate Change Canada (ECCC) only performs PM2.5 speciation monitoring in selected major urban centers of Canada (e.g., Edmonton, Toronto, Vancouver, Montreal) (ECCC, 2017a, Bari and Kindzierski, 2016b). In Alberta local airshed monitoring organizations work collaboratively with Alberta Environment and Parks to operate air quality monitoring networks and monitoring stations in cities, small towns and rural areas and measure real-time concentrations of gaseous pollutants and PM2.5. Due to lack of PM2.5 speciation data, numerous studies have been carried out worldwide to characterize sources of ambient fine particulate matter, nanoparticles, particle size distribution using real-time concentrations of gaseous pollutants data (e.g., Yue et al., 2008, Thimmaiah et al., 2009, Hellebust et al., 2010, Sun et al., 2014, Khan et al., 2015, Al-Dabbous and Kumar, 2015, Sowlat et al., 2016). Using only real-time gaseous pollutant data in receptor models may provide a limited number of source factors and may not be able to identify some specific sources (e.g., road dust, secondary organic aerosol, biogenic). In addition, this approach may also not be able to distinguish different industry-related sources (e.g., metallurgy, refinery, cement kiln) that can be important sources in urban areas of Alberta. However, the approach can offer useful preliminary information highlighting potential major emission source types that affect air quality at a receptor location in urban areas. In our recent studies (Bari and Kindzierski, 2017a, Bari and Kindzierski, 2017b), we used the positive matrix factorization (PMF) model to investigate PM2.5 sources in the third largest urban area (Red Deer) and a small rural community (Hinton) in Alberta using gaseous pollutant data. In this exploratory study, we characterized air quality and investigated emission sources that affect PM2.5 levels in the largest city of Alberta – Calgary using real-time continuous air monitoring data.
Section snippets
Study areas
As part of ECCC's National Air Pollution Surveillance (NAPS) initiatives, the Calgary Region Airshed Zone Society (CRAZ, http://www.craz.ca) has been responsible for regional air quality monitoring and providing results to Alberta Environment and Parks. The CRAZ airshed boundaries include the cities of Calgary and Airdrie, the Municipal Districts of Rocky View, Bighorn and Foothills, Willow Creek, Vulcan and Wheatland Counties, the Improvement Districts of Kananaskis and Banff, and the Town of
Levels of criteria air pollutants
Table 1 shows descriptive statistics of hourly concentrations of criteria air pollutants at Calgary central and Calgary northwest stations over the study period 2014–2016 (monthly profiles of hourly concentrations are presented in Fig. S4). The overall means and median concentrations of PM2.5 were similar at both Calgary central (arithmetic mean: 7.7 μg/m3, median: 6.0 μg/m3) and Calgary northwest (arithmetic mean: 7.5 μg/m3, median: 6.0 μg/m3). Elevated hourly 98th percentile concentrations of
Conclusion
An exploratory study of air quality and sources of PM2.5 concentrations was undertaken in the City of Calgary, Alberta for the period 2014 to 2016. Summer PM2.5 concentrations were relatively higher compared to other seasons. The 3-year averages of the annual average 24 h PM2.5 concentrations (8.1–8.9 μg/m3) were below the 2015 annual CAAQS value of 10 μg/m3. Observed summertime 24 h exceedances of the 2015 CAAQS at Calgary stations were primarily due to the influence of wildfire smoke
Acknowledgement
The authors gratefully acknowledge Alberta Environment and Parks for the provision of air quality and meteorological data, and the United States NOAA Air Resources Laboratory for the provision of the HYSPLIT model used for this investigation. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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