GTA Clean Air Council

What is a SMOG WATCH?

The Air Quality Ontario issues a Smog Watch based on the Air Quality Index (AQI). The AQI is a numerical rating scale for outdoor air quality in Ontario. The scale ranges from 0 to 100+ and takes into account six key pollutants. These are:

GOOD
Outdoor air quality is considered to be GOOD with no known health effects for the majority of the population as long as the AQI value remains below 32.

MODERATE
Once the AQI value rises to between 32 and 49, the Ontario Ministry of the Environment considers outdoor air quality to be MODERATE. Very sensitive people may experience adverse health effects at times of moderate air quality.

POOR
Poor outdoor air quality is reached when the AQI value is in the range of 50-99. At this level, the Ministry of the Environment advises that the most sensitive people and animals may face adverse health effects. Damage to vegetation and property may also occur.

VERY POOR
When Ontario’s air quality deteriorates to VERY POOR, an AQI value of 100 or higher has been reached. A large number of people, animals, vegetation and property may be adversely affected.

A SMOG WATCH is issued by the Ministry of the Environment when there is at least a 50% probability that smog conditions will occur within the next three days. The key reason behind issuing a smog watch is to warn people with breathing difficulties to avoid or minimize their exposure. Providing the public with advice as to what steps can be taken to reduce smog emissions is also important.