emissions from factory

Every summer, air pollution becomes a particular concern for municipalities across Ontario. Hot, smoggy air can be disruptive to outdoor activities and make life even more challenging for people who suffer from respiratory illnesses. While communities around the province do produce their own airborne emissions, our neighbours to the south end up exacerbating the problem.

The burning of fossil fuels in power plants, factories, homes, and vehicles is a major cause of air pollution. Those activities happen on both sides of the border, but unfortunately for us here in Ontario, American pollution doesn’t remain within American borders. From May through to September, prevailing winds from the United States run in a northeast direction, causing polluted air from the Ohio Valley, the Cleveland area, and the Detroit area to travel across southern Ontario, as well as southern Quebec and the Maritimes.

Within Ontario, a few cities’ meteorological and geographical locations make them especially vulnerable for polluted air.


In 2011, the World Health Organization released a massive compilation of air quality statistics for nearly 1,100 cities in 91 countries. In that report, the city of Sarnia was ranked as the worst city for air quality in Canada, having the most particulate matter per cubic metre of air. Coal-fired plants in the Ohio Valley and the Detroit area are partially to blame, as their emissions drift across the border and contribute to Sarnia’s poor numbers. Sarnia itself, however, is an industry-rich city. In 2007, Ecojustice Canada released a report that highlighted the fact that there are 62 large industrial facilities located within 25 kilometres of Sarnia (an area dubbed “Chemical Valley”), which emitted more than 131,000 tonnes of air pollution in 2005.


Another city notorious for poor air quality is Windsor, largely because of its climate and its proximity to Detroit. In a 2013 report that used data from 2011, the Ontario Environment Ministry noted that Windsor had the highest number of smog advisory days with eight. Windsor was also among the worst cities in the province for fine particulate matter, which can be especially detrimental to humans because it can penetrate deeper into the body’s airways. Those high particulate levels are the combined result of pollution from the United States, local industrial emissions, and truck traffic making its way around the region and across the border.


The city of Hamilton averages five smog advisories a year. Those advisories are issued when air quality is poor because of ground-level ozone and particulate matter. It’s not surprising that Hamilton needs to declare a few smog days each summer because the city, like so many others in Ontario, lies in the path of pollutant-laced air moving north from the Ohio Valley during the warmer summer months. In addition, Hamilton has a number of industrial facilities and several major highways running through it, and those elements add to the total air pollution.


Even though London does not have active industrial operations on the scale of Sarnia or Hamilton, its air quality can take a hit. Once again, its geographic location puts it in the path of moving currents of polluted air originating from the United States, but a wide range of local, small sources also contribute to air emissions, including vehicles, lawnmowers, and solvents used in homes and small industries. Moreover, high electricity use in the warmer months means a spike in air pollutants as local gas- and coal-fired plants meet the demand for power.


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