High levels of smog occur more often in summer, especially on sunny, hot and humid days. In Ontario, the Ministry of the Environment (MOE) reports daily on the Air Quality Index (AQI).
MOE website http://www.airqualityontario.com.
The AQI is a real-time measure of the quality of the air. It is rated as follows:
| 0-15 (very good) | no known harmful effects |
| 16-31 (good) | no known harmful effects; slight odour |
| 32-49 (moderate) | odour; respiratory irritation in sensitive people during vigorous exercise |
| 50-99 (poor) | odours; increased symptoms in those with cardiorespiratory diseases |
| 100+ (very poor) | increasing or serious symptoms for those with cardiorespiratory diseases. |
See Weather for more on the seasons in Mississauga
