Insights into urban concentrations and variability of NO₂, O₃, and PM_2.5 from the study of winter air pollution in Toronto (SWAPIT).

Authors

Selene Kutarna, Ralf M Staebler, Cristian Mihele, Yushan Su, Cheol-Heon Jeong, Greg Evans, Elisabeth Galarneau

Published in

Journal of the Air & Waste Management Association (1995). Pages 1-15. Nov 02, 2026. Epub Nov 02, 2026.

Abstract

The Study of Winter Air Pollution in Toronto (SWAPIT) was a research collaboration led by Environment and Climate Change Canada (ECCC) with the aim of understanding the composition, sources, and spatial variation of winter air pollution in Toronto. Air‑quality and wind data collected during a six-week period from January to March 2024 from eight continuous monitoring sites (SWAPIT and Partners) across Toronto was used to gain a better understanding of the concentrations and variability of nitrogen dioxide (NO₂), ozone (O₃), and fine particulate matter (PM_2.5). NO₂ was detected at higher concentrations under calm winds, indicating a stronger dependence on local sources, while O₃ was elevated at higher wind speeds consistent with regional transport. PM_2.5 showed features of both local and regional influence. The highest short-term health risks assessed by the Air Quality Health Index (AQHI) were dominated by NO₂ over the SWAPIT period and an examination of the historical National Air Pollution Surveillance (NAPS) data set showed that median city-wide AQHI values have decreased faster in summer than in winter, producing greater values in winter since 2013. The publicly reported community AQHI value for Toronto, calculated from data from four NAPS stations, was not always representative of values at other Toronto sampling sites, which showed maximum deviations of over 2 AQHI units above and below the community values during the study period. Semi-quantitative evaluation of observations relative to Canadian Ambient Air Quality Standards (CAAQS) and World Health Organization (WHO) Air Quality Guidelines suggested that all three pollutants continue to pose concerns in Toronto. This is consistent with recent health‑impact analyses that estimate over 1,200 premature deaths in the City of Toronto due to air pollution each year, and supports continued efforts to understand air‑pollution sources and impacts in Toronto and other urban areas.Implications: This study used air quality and wind data collected during a six-week period from eight continuous monitoring sites across Toronto to gain a better understanding of the differences between winter and summer air quality. Short-term health risks as assessed by the Air Quality Health Index (AQHI) were dominated by NO₂ over the winter study period and an examination of the long-term NAPS data set from 1997 onward showed that median AQHI values have decreased at almost twice the rate in summer as in winter, leading to greater values in winter since 2013. These results support continued efforts to understand air‑pollution sources and impacts in Toronto and other urban areas.

PMID:
42970662
Bibliographic data and abstract were imported from PubMed on 03 Nov 2026.

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