Afp, Paris
Air quality is improving in countries under coronavirus quarantines, experts say, but it is far too early to speak of long-term change.

Images taken by by the US space agency Nasa in February showed the concentration of nitrogen dioxide (NO2) fell dramatically in Wuhan, China, the epicentre of the COVID-19 pandemic.

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.

The European Environment Agency (EEA) reports a similar change in Barcelona and Madrid, where Spanish authorities issued confinement orders in mid March.

In northern Italy, "average NO2 concentration levels have been almost halved on average," Peuch remarked.

As for other countries or regions that have told inhabitants to remain confined at home, notably Argentina, Bavaria, Belgium, California, France and Tunisia, specialists are poring over the data to see if the trend is similar.

Meanwhile, less NO2 does not necessarily mean purer air. Beijing experienced episodes of pollution owing to fine particles in February, Nasa's Earth Observatory reported.

The air in Paris was also rated as moderately polluted Friday owing to the presence of fine particles and NO2 even though the population had already been confined at home for three days.

Confinement measures protect in two ways, by reducing the risk of COVID-19 infection and by easing pollution from road traffic, according to a group of French doctors known as Air-Sante-climate.

It is nonetheless hard to know how much benefit the world's population will actually experience. According to the health experts, that will depend on how long the meaures will last.