2016 Highlights

Overall, air quality in Ontario has improved significantly over the past 10 years due to substantial decrease in harmful pollutants such as nitrogen dioxide, sulphur dioxide and carbon monoxide that are emitted by vehicles and industry.

There has also been a significant decrease in fine particulate matter which is emitted directly into the atmosphere as a by-product of fuel combustion or formed indirectly in the atmosphere through a series of complex chemical reactions. Fine particulate matter includes aerosols, smoke, fumes, dust, fly ash and pollen, and can have various negative health effects, especially on the respiratory system.

The continued decrease in these pollutants is due in part to Ontario’s air quality initiatives such as:

  • The phase-out and banning of coal-fired generating stations. The ban not only helped reduce the number of harmful contaminants entering the air, but it was also one of the largest greenhouse gas reduction initiatives in North America.
  • Nitrogen oxides and sulphur dioxide emissions cap and trade regulations, (O. Reg. 397/01 and O. Reg. 194/05)
  • Setting new and updated air standards through the local air quality regulation (O. Reg. 419/05)
  • Regulating industrial emissions through the site-specific standard and technical standard compliance options under O. Reg. 419/05
  • Establishing emissions controls at Ontario smelters through site-specific standards under O. Reg. 419/05
  • Drive Clean testing of vehicle emissions
Trends in Ambient Air Concentrations and Air Emissions, 2007-2016

NO2 is the concentration measured and NOx is the emission estimated.
Ozone is a secondary pollutant. It is not directly emitted and only formed when NOx and VOCs react in the presence of sunlight; therefore emission trends are not available.

Trends in Volatile Organic Compounds, 2007-2016
m-, p-xylene53%
1,3 butadiene50%


This annual report, the 46th in a series, summarizes the state of ambient air quality in Ontario during 2016 and examines 10-year trends. It reports on the measured levels of six common air pollutants: nitrogen dioxide (NO2), fine particulate matter (PM2.5), ground-level ozone (O3), carbon monoxide (CO), sulphur dioxide (SO2) and total reduced sulphur (TRS) compounds, and how Ontario is performing compared to the province’s Ambient Air Quality Criteria (AAQC). The ambient air monitoring sites featured in this report are generally representative of regional air quality which is less influenced by local and industrial sources of air contaminants. This report also provides an overview of the Air Quality Health Index (AQHI) and Air Quality Alert programs in Ontario, plus the monitoring of select volatile organic compounds (VOCs) in the province. Annual statistics, as well as 10-year trends of ambient air quality data are provided in the attached Appendix.

An AAQC is a desirable concentration of a contaminant in air, based on protection against adverse effects on health or the environment. The term “ambient” is used to reflect general air quality independent of location or source of a contaminant. AAQCs are most commonly used in environmental assessments, special studies using ambient air monitoring data, assessment of general air quality in a community and annual reporting on air quality across the province. AAQCs are set with different averaging times appropriate for the effect they are intended to protect against. The effects may be health, vegetation, soiling, visibility, corrosion or other effects. AAQCs may be changed from time to time based on new science.

Contaminant1-hour AAQC8-hour AAQC24-hour AAQCAnnual AAQC
NO2200 ppbn/a100 ppbn/a
PM2.5n/an/a28 µg/m3footnote 1n/a
O380 ppbn/an/an/a
SO2250 ppbn/a100 ppb20 ppb
CO30 ppm13 ppmn/an/a

ppb – parts (of contaminant) per billion (parts of air) – by volume.
µg/m3 – micrograms (of contaminant) per cubic metre (of air) – by weight.
ppm – parts (of contaminant) per million (parts of air) – by volume.

Ontario continues to benefit from one of the most comprehensive air monitoring systems in North America, comprised of 39 monitoring sites across the province that undergo regularly scheduled maintenance and strict data quality assurance and quality control (QA/QC) procedures to ensure a high standard of data quality and data completeness. The data, which are collected continuously at these sites, are used to determine the current state of ambient air quality and are reported every hour on the ministry’s web site.