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.

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"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.