Graphic detail | Blue skies turn grey

Air pollution is returning to pre-covid levels

This bodes ill for respiratory health

COVID-19 IS NOT all bad, as any city-dweller who stepped outside this year will have seen. The virus has killed hundreds of thousands of people and decimated economies around the world. But as GDP has fallen so has air pollution. This spring marked the first time in decades that residents of Jalandhar in northern India were able to see the snow-capped Himalayan mountains, 160km (100 miles) away.

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One particularly common pollutant is nitrogen dioxide (NO2). The World Health Organisation (WHO) reckons that NO2 levels above 40 micrograms in every cubic metre of air (40µg/m3) are harmful to people. In Delhi, one of the world's most polluted big cities, NO2 fell sharply after the city imposed its lockdown, from 46µg/m3 in March to 17µg/m3 in early April. Similarly, NO2 levels in London fell from 36µg/m3 in March to 24µg/m3 two weeks later.

Air-pollution levels do not depend on human activity alone—weather conditions such as wind speed, rainfall and humidity matter, too. The Centre for Research on Energy and Clean Air (CREA), a think-tank, has produced a model which takes these factors into account to gauge the impact covid-19 has had on air-pollution levels in 12 big cities around the world. They found that NO2 levels fell by about 27% ten days after governments issued stay-at-home orders, compared with the same period in 2017-19. Levels of particulate matter less than 2.5 micrometres wide (PM2.5), which are also harmful to health, declined by an average of about 5% in a group of 12 big cities in which data are readily available.

The health benefits of cleaner air are profound. The WHO reckons that about 90% of the world’s population live in places where air quality falls short of its standards. They estimate that 4.2m people died prematurely from diseases related to air pollution, such as respiratory-tract infections and lung cancer, in 2016 alone, including 290,000 children. Millions more suffer from chronic health problems.

The CREA estimates that improved air quality since the covid-19 pandemic began has saved about 15,000 lives in 12 big cities. In Delhi, around 4,600 people have escaped death due to air pollution—roughly as many as are known to have died from covid-19, although the disease’s true tally is probably higher and still rising.

As people return from summer holidays in the northern hemisphere and economies begin to recover, air pollution is nearing pre-pandemic levels. Although people are still wary of using public transport, they appear to have fewer reservations about driving cars themselves—data from TomTom, a location-tech firm, show that congestion in big cities has just about returned to pre-covid levels. This increase in pollution will be deadly, especially to those who suffer from severe asthma, who are also vulnerable to covid-19.

Sources: Centre for Research on Energy and Clean Air; TomTom;The Economist

This article appeared in the Graphic detail section of the print edition under the headline "Blue skies turn grey"

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