Dramatic reductions have been made in several air pollutants in Ontario during the past three decades. Unfortunately, one major pollutant of concern, ground-level ozone, has increased steadily in the environment over the past 20 years. Significant human health effects are occurring at current concentrations.
The Ontario Medical Association stated in a June 2001 report that, "This review finds a worrying situation in recent trends in Ontario's air quality. We see:
- Increases in ozone levels
- No change in particulate levels
- A stalling of earlier progress in the reduction of the building blocks of smog: nitrogen oxides (NOx), sulphur dioxide (SO2) and volatile organic compounds (VOCs)."3
Nitrogen oxides (NOx) and volatile organic compounds (VOCs) are the main pollutants that cause the formation of ground-level ozone. Ministry of the Environment data for the Toronto area show that emissions of NOx from automobiles and heavy duty trucks account for approximately 50% of all local emissions (80% if off-road vehicles are included). Several other air pollutants of concern to human health are also increased by vehicle use related to urban sprawl, including fine particulates, volatile organic compounds, sulphur dioxide, and carbon monoxide, as well as carbon dioxide (which exacerbates the health effects of the other pollutants due to its role in causing global climate change).
The impact of urban sprawl on transportation and related air emissions, such as CO2, is shown below:4
Travel and Other Characteristics of Four Concentric Parts of the Toronto Region
Residential density (urbanized portion, persons/square km.)
Percentage of households owning one or more cars
Travel by car (km/person/day)
Total travel by motorized transport (km/person/day)
Estimated CO2 emissions resulting from travel (grams/person/day)
In recent studies, the U.S. Environmental Protection Agency has found that infill development and re-development of older suburbs could reduce vehicle kilometres travelled per capita by 39 to 52 percent (depending on the metropolitan area studied) compared to urban sprawl.5 Thus, the relationship between urban form, transportation emissions and air quality is clear, with urban sprawl being a major factor related to air pollution.