Pollution has dropped in major US cities as America shuts down to halt the spread of the coronavirus.

Satellite images show nitrogen dioxide (NO2) concentrations from 10 March to 22 March, 2020 compared to the same period last year.

NO2, represented by the colour density on the maps, is shown to be in remarkably lower concentrations this month over New York, Los Angeles, Chicago, Denver, Detroit and Houston.

The analyses of NO2 emissions were provided to The Independent by Descartes Labs, a geospatial analysis group. The images, using the European Space Agency’s Sentinel-5P satellite data, represent weighted mean NO2 concentrations.

Millions of Americans have been ordered to stay home in the hope of slowing the​ Covid-19 outbreak. There has been a surge in recent days, leading to 43,500 confirmed cases and 541 deaths.

The 40m residents of California were ordered to stay home last week after increasing restrictions on movement and non-essential businesses being ordered to close.

Governor Andrew Cuomo told New York residents to stay home and ordered the close of all non-essential businesses on Sunday.

Chicago, which also has noticeably lower levels of NO2, and the rest of the state of Illinois is under a stay-at-home order, beginning this week. 

The US and Canada have closed their borders to non-essential travel.

Nitrogen dioxide levels in the atmosphere in part come from cars, trucks, buses and power plants, according to the Environmental Protection Agency.

The air pollutant forms when fossil fuels like coal, oil, gas or diesel are burned at high temperatures. Along with other nitrogen oxides, NO2 contributes to particle pollution in the air.

It can cause a range of health issues, according to the American Lung Association, including increased inflammation of airways; cough and wheezing and reduced lung function. The group also points to new research which warns NO2 to be the likely cause of asthma in children.

Fei Liu, an air quality researcher at NASA’s Goddard Space Flight Center, told CNN: “This is the first time I have seen such a dramatic drop-off over such a wide area for a specific event. I am not surprised because many cities nationwide have taken measures to minimize the spread of the virus.”

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