Smog Watch and Smog Advisory
How is smog measured?
The Ministry of Environment measures the air quality in Ontario using a rating scale called the Air Quality Index (AQI). The scale ranges from 0 to over 100 - the lower the AQI number, the better the air quality.
The AQI is based on six key air pollutants including: sulphur dioxide, ozone, nitrogen dioxide, carbon monoxide, total reduced sulphur and particulate matter. Each hour, the concentration of the six pollutants is measured at particular stations across Ontario. There are 11 monitoring stations across the GTA. Two of those stations are located in Peel - one in Brampton and one in Mississauga - and five are located in areas bordering Peel region.
The pollutant with the highest number at the given hour becomes the AQI.
An AQI value between 0-15 is considered very good, between 16-31 good and between 32-49 moderate.
An AQI of 50-99 is considered poor and over 100 is very poor. When the AQI is predicted to reach or exceed 50, a smog advisory is issued.
What is a smog watch?
The Ministry of Environment issues a smog watch when there is at least a 50 per cent probability that the AQI will reach or exceed 50 in the next three days.
What is a smog advisory?
The Ministry of Environment issues a smog advisory when there is a high probability that the AQI will reach or exceed 50 in the next 24 hours.
How do I know if there is a smog watch or a smog advisory?
Check the Ontario Ministry of Environment website for current air quality readings and forecasts.
Call the Ontario Ministry of Environment's Air Quality Index phone line for current air quality forecasts.
For English: call 1-800-387-7768 or 416-246-0411 in Toronto.
For French: call 1-800-221-8852
Join the Ontario Ministry of Environment's Smog Alert Network and you can receive an automatic e-mail when a smog watch or smog advisory is issued. You can also sign up for this service.