The Air Quality Ontario website of the Ontario Ministry of Environment and Climate Change states:
The contaminants that create smog are released during the combustion of fossil fuels in our vehicles, power plants, factory boilers and homes. They are also released by industrial processes, the evaporation of liquid fuels and the use of solvents and other volatile products such as oil-based paints. Smog-causing contaminants are released during forest fires, and emitted by natural sources such as: trees, bogs, and volcanic activity. Most of Ontario’s smog problems are caused by a combination of local emissions and pollutants carried by the wind from pollution sources in the United States. More than half of our smog problem comes from south of the border.
The Air Quality Index (AQI) for Ontario is an indicator of our air quality, based on pollutants that have adverse effects on human health and the environment. The pollutants are ozone, fine particulate matter, nitrogen dioxide, carbon monoxide, sulphur dioxide and total reduced sulphur compounds.
If the AQI falls below 32, the air quality is considered good or very good. An AQI reading between 32 and 49 indicates moderate air quality, and an AQI reading from 50 to 99 indicates poor air quality. A reading over 99 indicates very poor air quality.
The ministry utilizes a network of 40 air monitoring stations across Ontario to help predict impending smog problems. A Smog Watch is issued when there is a 50 per cent chance that elevated smog levels are forecast to occur within the next three days. A Smog Advisory is issued when there is a strong likelihood that elevated smog levels are forecast to occur within the next 24 hours, or it can be issued immediately if widespread, poor AQI readings occur, and weather conditions conducive to the persistence of such levels are expected to continue for several hours. Upon a change in the weather that results in cleaner air, the ministry issues an advisory termination notice.
The ministry issues a smog advisory immediately if widespread, poor AQI readings occur, and weather conditions conducive to the persistence of such levels are expected to continue for several hours.
Source: Ontario Ministry of Environment and Climate Change
Retrieved From: http://www.airqualityontario.com/press/faq.php#5
Air Quality Ontario reports the number of Smog Advisories and Smog Days between 2003 and November 22, 2014, for Ontario regions and cities.
The following chart shows the numbers for Ontario, Hamilton, Ottawa, Toronto and Niagara.
There are 40 Air Quality Ontario Ambient Air Monitoring Sites, and they provide online readings of air pollutant concentrations. There is one in the Niagara Region and it is located in St. Catharines. By clicking on the “retrieved from” link below, you can see the current readings at the St. Catharines site.
Source: Air Quality Ontario
Retrieved From: http://www.airqualityontario.com/history/station.php?stationid=27067
An annual status report of the Greenhouse Gas Inventory of Canada can be found on the World Health Organization website.
Source: World Health Organization
Retrieved From: https://unfccc.int/national_reports/annex_i_ghg_inventories/national_inventories_submissions/items/8108.php
The Air Quality in Ontario Report for 2011, issued by the Ontario Ministry of the Environment, states:
Overall, air quality has improved significantly over the past 10 years, especially for nitrogen dioxide (NO2), carbon monoxide (CO) and sulphur dioxide (SO2) – pollutants emitted by vehicles and industry, as well as fine particulate matter (PM2.5), which may be emitted directly or from other emissions such as SO2.
Ozone is a secondary pollutant formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight. Ozone annual means have increased by 7 per cent from 2002 to 2011, however, ozone summer means continue to show improvement and have decreased by 9 per cent over the same period.
Source: Air Quality in Ontario Report for 2011
Retrieved From: http://www.airqualityontario.com/downloads/AirQualityInOntarioReportAndAppendix2011.pdf