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Air Quality

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Key Findings

  • Vehicular, rail and industrial emissions were identified as significant sources contributing to overall air quality conditions within the Study Area
  • Current annual emissions of exhaust contaminants and greenhouse gases (GHGs) were estimated for traffic and rail sources within the Ontario Line West, Ontario Line South, and Ontario Line North segments of the Study Area
  • Existing baseline air quality concentrations of critical contaminants and GHGs from representative ambient air quality monitoring stations were examined and compared against provincial and federal air quality thresholds. Most contaminants were found to be below their respective thresholds, with the exception of benzene and benzo(a)pyrene exceeding Provincial Ambient Air Quality Criteria (AAQC)


Ontario West

  • 42,880 tonnes of greenhouse gas (CO2e)
  • 50 tonnes of Nitrogen Oxides (NOX)
  • 243 tonnes of Carbon Monoxide (CO)
  • 0.259 tonnes of SO2
  • 8 tonnes of Particulate Matter (PM10 & PM2.5)

Ontario South

  • 47,672 tonnes of greenhouse gas (CO2e)
  • 45 tonnes of Nitrogen Oxides (NOX)
  • 239 tonnes of Carbon Monoxide (CO)
  • 0.262 tonnes of SO2
  • 13 tonnes of Particulate Matter (PM10 & PM2.5)

Ontario North

  • 11,816 tonnes of greenhouse gas (CO2e)
  • 18 tonnes of Nitrogen Oxides (NOX)
  • 64 tonnes of Carbon Monoxide (CO)
  • 0.086 tonnes of SO2
  • 5 tonnes of Particulate Matter (PM10 & PM2.5)


Spotlight Case

Traffic emission contributions were inventoried as part of the review of air quality ambient background levels and contributing factors to local air quality. Much of the Study Area is indicative of a typical “downtown” condition in terms of baseline emissions– with passenger vehicles contributing to contaminants and greenhouse gas emissions. The eastern and northern portion of the Study Area is indicative of a mixture of the same typical “downtown” traffic emissions and a more “residential” profile of traffic emissions. Emissions from traffic include contaminants produced from combustion, including carbon monoxide (CO), nitrogen oxides (NOX), sulphur dioxide (SO2), a range of volatile organic compounds, and fine particulates. The heavier the traffic, the higher the concentration of these parameters.

Image depicting traffic congestion and emmissions

Traffic Emission Contributions

Source: Getty Images (n.d.). https://www.utoronto.ca/sites/default/files/GettyImages-1085693600.jpg


Air quality was assessed in the Study Area, including examining vehicle exhaust and GHGs. The assessment was based on publicly available historical data from ambient air quality monitoring stations close to the Study Area Potential sources of contaminants examined included:

  • Vehicular emissions
  • Diesel rail emissions
  • Industrial emissions


Preliminary Potential Impacts & Mitigation Measures for Further Study


Potential Impacts

  • Air pollution as a result of construction vehicle emissions
  • Dust resulting from earthworks, demolition and construction

Potential Mitigation Measures

  • Contain (e.g., tarp) sources of dust such as soil stockpiles, as required
  • Use dust suppressants such as water, as required
  • Use equipment with low emissions, to the extent possible


  • No impacts to air quality are anticipated as a result of operations

Future Studies

  • Using the baseline information and identified preliminary impacts, a future impact assessment will be conducted


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