Air pollution has decreased in urban areas across Europe during lockdowns to combat the coronavirus, new satellite images showed on Monday, but campaigners warned city-dwellers were still more vulnerable to the epidemic.

Cities including Brussels, Paris, Madrid, Milan and Frankfurt showed a reduction in average levels of noxious nitrogen dioxide between March 5 and March 25 compared with the same period last year, according to the Sentinel-5 satellite images.

That coincides with lockdowns in many European countries which have curbed road transport the largest source of nitrogen oxides and slowed output at gas-emitting factories.