Air quality improves in quarantined areas

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

Images by US space agency Nasa are clear. Last month, the concentration of nitrogen dioxide (NO2) fell dramatically in Wuhan, China, the first 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.

But as China moves past the peak of its crisis, 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 was locked down to fight the spread of the coronavirus.

The European Environment Agency reports a similar change in Barcelona and Madrid, where the authorities issued confinement orders in the middle of this month.

"NO2 is a short-lived pollutant, with a lifetime in the atmosphere of about one day," Dr Vincent-Henri Peuch of the European Union earth surveillance programme Copernicus told Agence France-Presse.

"As a result, this pollutant stays near the emissions sources and can be used as a proxy of the intensity of activity in different sectors."

Noting the change in China, air quality researcher Fei Liu at Nasa's Goddard Space Flight Centre said: "This is the first time I have seen such a dramatic drop-off over such a wide area for a specific event."

Dr Peuch said that in northern Italy, "average NO2 concentration levels have been almost halved on average". The pollutant can provoke serious inflammation of the respiratory system.

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

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

Dr Peuch said the concentration of polluting matter can vary with the weather, noting: "Some emissions sources, like energy production and residential use of energy, are likely not to be decreasing markedly when more people have to stay at home." The concentration of so-called PM2.5 and PM10 particles and carbon monoxide are "also expected to be reducing over time".

Air pollution causes around 8.8 million premature deaths each year, according to a recent study.

Fine particles irritate the eyes and throat and inhibit breathing. In extreme cases, the elderly and those who suffer from asthma risk death if not properly treated. In the longer term, air pollution can cause chronic respiratory or cardiac problems or lung cancer.

Confinement measures thus 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.

AGENCE FRANCE-PRESSE