Public health measures shutting down workplaces and schools to fight the COVID-19 pandemic have led to a noticeable reduction in air pollution in multiple Canadian cities known for their traffic congestion, according to satellite images shared with CBC News.

Toronto, Edmonton, Calgary and Vancouver have seen drops in vehicle traffic over the last few days as physical distancing measures introduced to slow the spread of the novel coronavirus have kept Canadians closer to home.

Images from Descartes Labs of the major cities and surrounding areas show their average levels of atmospheric nitrogen dioxide (NO2)— a pollutant created by the burning of fossil fuels, such as gasoline — has plummeted compared to a year ago. The New Mexico-based geospatial analysis group shared the data with some news organizations, including CBC and the New York Times.

The composite images come from the European Space Agency's Sentinel 5P satellite and show averages over time.

"It seems pretty clear to us that things are slowing down in cities because of the outbreak," Tim Wallace, the head of creative at Descartes Labs, told CBC News.

Most NO2 emissions come from vehicles. The gas has a pungent odour and in high concentrations it can irritate the lungs and cause coughing, wheezing and difficulty breathing. Prolonged exposure has been linked to the development of asthma and other illnesses, according to the U.S. Environment Protection Agency.

Toronto

According to the traffic analysis firm Inrix, Toronto was the most congested city in Canada in 2019 and the 19th most congested in the world. Ontario's residents were asked by their provincial and federal governments to stay home in March — the clear reduction in NO2 levels since then shows that they've been listening. Other cities, including Oshawa, Brampton and Hamilton, have also seen declines. (You can move the slider on the images below to see the year over year differences.)

Edmonton and Calgary

Edmonton and Calgary both saw similar emission declines within their urban cores and along Hwy 2, the main artery that connects the two cities.

Vancouver

British Columbia has been outpacing the rest of Canada in the adoption of electric vehicles and the province is considered by some to have a robust "green culture." But even those on the West Coast might be breathing a bit easier lately as the city and its surrounding areas see less traffic.

Impact on greenhouse gas emissions?

Nitrogen dioxide should not be confused with greenhouse gases – but because it and carbon dioxide are both produced when fossil fuels are burned, there is a relationship between levels of NO2 and carbon dioxide emissions — the gas most associated with climate change.

"These are striking reminders of the impacts of the way that we are living now and our striking use of fossil fuels," said Michael Brauer, a professor in the School of Population and Public Health at the University of British Columbia.

Ryan Katz-Rosene, president of the Environmental Studies Association of Canada, said that the world should see a decline in greenhouse gas emissions as result of this pandemic.

And while the immediate concern should be the health and well-being of citizens, Katz-Rosene, an assistant professor of political studies at the University of Ottawa, said policymakers should use this time to consider how post-pandemic stimulus and recovery money could be directed at creating jobs in clean tech, encouraging companies to use less carbon-intensive technology and building greener transportation networks.

Two security guards walk through downtown Vancouver on Monday, March 23, 2020. (Ben Nelms/CBC)

"(We need to make) sure that we use the post-pandemic stimulus packages to work toward a just transition," he said.