The European Union's space agency satellites have detected a reduction in the pollutant nitrogen dioxide, a byproduct of diesel motors and other human activity, in northern Italy as the coronavirus leads to shutdowns.

The agency's Copernicus Atmosphere Monitoring Service reported on Tuesday that with the "abrupt changes in activity levels" in northern Italy, it has tracked a "reduction trend" of nitrogen dioxide, or NO2, for the last four to five weeks.

So far, Italy has been the hardest-hit country in Europe by the new coronavirus, and the government has implemented a wide lockdown, encouraging its 62 million people to stay home unless it's absolutely necessary to go out.

Similar drops in pollutants were detected in China after the government there implemented widespread shutdowns to try and slow the spread of COVID-19.

NO2 is a short-lived pollutant, staying in the atmosphere generally less than a day before being deposited or reacting with other gases, meaning it remains fairly close to where it was emitted, the agency said.

Most emissions are generated by human activities such as traffic, energy production, residential heating and industry.

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"It is quite remarkable that a signal of decreasing activity levels could be detected," said Vincent-Henri Peuch, the director of the Copernicus Atmosphere Monitoring Service.

"This shows the extent of the measures taken by Italy."