Air quality is improving in countries under coronavirus quarantines, experts say, but it is far too early to speak of long-term change.
Images by the U.S. space agency NASA are clear, in February the concentration of nitrogen dioxide (NO2) fell dramatically in Wuhan, China, the epicentre of the COVID-19 pandemic, passing from an indicator that was red/orange to blue.
NO2 is mainly produced by vehicles, industrial sites and thermal power stations.
As China moves past the peak of its crisis, however, recent images by the European Space Agency (ESA) show a resurgence in NO2 emissions.
A striking reduction has also been observed by the ESA in northern Italy, which has been locked down to fight a spread of the novel coronavirus, which causes COVID-19.