COVID-19 restrictions cut downtown Toronto pollution levels by almost half, researchers find


Researchers at the University of Toronto have discovered a substantial reduction in pollution levels in the downtown core since the province announced measures to curb the the spread of COVID-19, including shuttering schools and non-essential businesses. 

"A pandemic is not a good thing," said Greg Evans, director of the Southern Ontario Centre for Atmospheric Aerosol Research (SOCAAR). 

"But seeing the change ... gives us a better understanding of the many factors that contribute to poor air quality." 

The SOCAAR team analyzed the concentration of dozens of pollutants from air pulled directly from a duct off College Street in downtown Toronto for 24 days before March 13 and 24 days after. 

The preliminary results provided to CBC News showed levels of nitrogen oxides and ultrafine particles, both indicative of vehicle pollution, have sharply decreased, a finding consistent with the reduction in traffic in the area. 

"Both of them have dropped by about half," said Evans. 

At this point, Evans says he isn't able to attach an exact percentage to the decrease because several factors affect the accuracy of that number, including the level of travel over March break and the onset of spring. 

Evans says the data his team compiled is more specific and detailed than pollution data from satellite imagery, which gives a big-picture view.

"We can get a picture of what's going on right now at a given location." 

It's too early to draw conclusions about the impact on carbon dioxide levels, according to Evans, because it's been in the air for so long — one molecule of carbon dioxide stays in the atmosphere for about 40 years, so a drop over just a few weeks "really doesn't make that much of a difference to overall levels." 

As he collects more data, though, Evans said he may be able to draw more conclusions.