Hamilton, a medium-sized city on the western shore of Lake Ontario, has long been associated with air quality challenges due to its steel production, industrial operations, and heavy traffic. The city's geography, divided by the Niagara Escarpment into the Lower City (encompassing downtown and industrial zones) and the Upper City, and its proximity to Lake Ontario further exacerbates these challenges. The Lower City's industrial activity and traffic emissions, combined with geographic constraints, often lead to trapped pollutants and deteriorating air quality.

To better understand the composition of PM2.5 in Hamilton, an 18-month air quality study was conducted from January 12, 2021 to July 16, 2022 using data collected by the ministry at its Hamilton Downtown AQHI air monitoring station. The study focused on identifying the components of PM2.5 in the Lower City and determining their potential sources. The findings revealed the following composition of PM2.5 mass in the Lower City:

  • secondary organic aerosols mainly related to long-range atmospheric transport of pollution (Type 1): 40%
  • particulate nitrate: 27%
  • particulate sulphate: 16%
  • primary traffic-related organic matter: 11%
  • traffic-related black carbon and steelmaking: 5%
  • secondary organic aerosols related to atmospheric processing of local emissions (Type 2): 1%

To distinguish local pollution sources from regional contributions, dispersion normalization techniques were employed, which involved analyzing pollutant responses to local weather conditions. The study showed that the main sources of fine particulate matter in the Lower City included local traffic, local industrial activities and sources outside of Hamilton or regional sources. Traffic related pollution was higher in winter, especially on weekdays. Seasonal patterns showed that sulphates peaked in summer, nitrates and traffic-related pollution were highest in winter, and local pollution levels were at their maximum in spring. During summer, PM2.5 levels were significantly impacted by wildfires and regional sources, while winter saw increased particulate nitrate levels due to local traffic emissions and cold weather conditions. Over time, local industrial and traffic pollution exhibited a clear pattern, peaking during weekday morning rush hours.

The study highlighted the dual nature of Hamilton's PM2.5 pollution sources. In summer, regional influences like wildfires played a dominant role in elevating PM2.5 concentrations. In contrast, winter air quality was significantly impacted by local emissions, particularly from traffic. These insights underscore the need for targeted strategies to address both local and regional pollution sources to improve Hamilton's air quality.

Additional information on Hamilton's air quality and related topics can be found in the journal publications listed below. Common findings in these studies include the long-term decrease in PM2.5 concentrations. Biomass burning and particulate sulphate contributions to ambient PM2.5 in Hamilton are also in decline while sources related to industry in Hamilton such as coal combustion/coking and steelmaking emissions have stable trends.

Learn more about what Ontario is doing to protect our air.