Most polluted global major city ranking on July 17, 2026

At 9:00 a.m., Toronto's AQI (Air Quality Index) rating ranked fifth worldwide at 172.

AQI 0-50 Good, 51-100 Moderate, 101-150 Unhealthy for sensitive groups, 151-200 Unhealthy, 201-300 Very unhealthy, 301+ Hazardous

Air Quality Index (AQI) is a system that combines pollutant concentration figures into a single number. The number usually weighs up to six key pollutants (PM2.5, PM10, carbon monoxide, sulfur dioxide, nitrogen dioxide and ground level ozone), as both the American and Chinese systems do, according to IQAir. AQI calculates the health risk for each pollutant at a given time, and the overall AQI number is dictated by the "riskiest" pollutant with the highest AQI number.
Source: iqair