Daily weather events can influence atmospheric pollution, so the satellite pictures took a 20-day average and excluded readings where cloud cover reduced the quality of the data.
Data from the European Environment Agency (EEA) showed a similar trend over March 16-22. In Madrid, average nitrogen dioxide levels decreased by 56 per cent week-on-week after the Spanish government banned non-essential travel on March 14.
The EPHA said people living in polluted cities may be more at risk from COVID-19, because prolonged exposure to bad air can weaken the immune system, making it harder to fight infection.
“That connection is very likely,” Zoltan Massay-Kosubek, policy manager for clean air at EPHA, told Reuters. “But because the disease is new, it still has to be demonstrated.”
Air pollution can cause or exacerbate lung cancer, pulmonary disease and strokes. It causes around 400,000 premature deaths each year in Europe, EEA data show.
China also recorded a drop in nitrogen dioxide pollution in cities during February, when the government imposed lockdown measures to contain the raging epidemic.
In some regions of Poland, however, nitrogen dioxide levels remained relatively high during the period despite its lockdown, perhaps due to the prevalence of coal-based heating.
Countries that went into lockdown later – such as Britain, which did so on March 23 – look set for a pollution reprieve in coming weeks, EPHA said.
The environmental news comes as a senior British medical official said some lockdown measures may last six months.
“The important thing is this is a moving target,” Deputy Chief Medical Officer Jenny Harries said.
“If we do well it moves forward and comes down and we manage all our care through our health and care systems sensibly in a controlled way and that is what we are aiming for,” she told a news conference.
“This is not to say we would be in complete lockdown for six months but it means that as a nation we have to be really, really responsible and keep doing what we are all doing until we are sure that we can gradually start lifting various interventions.”
The human cost of the coronavirus continued to mount as death tolls came in from around Europe over the weekend.
Britain reported 19,522 confirmed cases of the disease and 1228 deaths, after an increase of 209 fatalities compared with the previous day, the Health Ministry said. The daily tally only accounts for those dying in hospital – the addition of data this week on deaths in retirement homes is likely to result in a big increase in registered fatalities.
Spain reported 838 new deaths in the previous 24 hours, its highest daily number yet.
But in a small glimmer of hope, the pace of increases in deaths slowed for a fourth day in Spain, deaths in Italy fell for a second day with 756 deaths reported, and new infections were rising more slowly in both countries.
In France, health authorities reported 292 new deaths on Sunday, up 13 per cent on the previous day and taking the total to 2606 since March 1.