Toronto air quality currently ranks among the worst in the world. Here’s why.

A heat warning has been issued for Toronto, as humidex values approach 45. Rahim Ladhani reports.

The air quality in Toronto is currently ranked among the worst in the world, on top of a multi-day heatwave that’s gripping the city Monday.

According to IQAir, which tracks air quality data from across the globe, Toronto is the 30th most polluted city at time of writing.

Meanwhile, Environment Canada’s Air Quality Health Index (AQHI) lists the air in Toronto as a Level 5, or moderate risk.

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The national weather agency had warned that the hot and humid air brought on by the heatwave could produce “deteriorating” air quality, and meteorologist Geoff Coulson says that’s what we’re seeing here.

“We have, generally, a subsiding or sinking motion associated with the high-pressure system that’s affecting us, and that sinking air can create inversions in the atmosphere.”

Coulson explained that because the hot air is impeded from rising, pollutants are trapped in the lower levels of the atmosphere and affect air quality. He said while it’s unlikely wildfire smoke from Quebec and northern Ontario are having an impact on air quality right now, that could change later this week.

• READ MORE: Toronto enters another heat wave this week. Here is how hot it will get

“It looks like by Wednesday we could be seeing some enhanced levels of particulate matter 2.5 from the wildfires in northwestern Ontario,” he said.

Under a Level 5 AQHI, the general population does not need to modify usual outdoor activities unless they experience symptoms such as coughing or throat irritation. Those among the at risk population, such as seniors, pregnant women and infants, should consider reducing or rescheduling strenuous activities outdoors if experiencing symptoms.

Toronto is currently under a yellow-level heat warning, with temperatures above 30 C until Friday. Tuesday will be the hottest day with a high of 37 C, which will feel like 45 with the humidex.