Last reviewed 18 May 2020

Caroline Hand hopes that the lockdown has given us the impetus to maintain the current welcome drop in air pollution, in the third of our series of features on the relationship between the coronavirus and the environment.

From LA to Delhi, people are looking up at blue skies and breathing clean air: an unexpected consequence of the worldwide coronavirus lockdown. Within weeks of the introduction of restrictions, concentrations of pollutants in major cities had fallen by as much as 40%. Is a return to the former levels of pollution inevitable once economic activity resumes or will this episode demonstrate that cleaning up our air is within our reach if we are willing to take drastic action?

How has pollution affected COVID-19?

In every major city, people breathe air contaminated with a variety of pollutants, particularly nitrogen dioxide and particulates (including PM2.5).

Nitrogen dioxide, particulates and other pollutants have long been known to harm public health (particulates lodge in the lungs causing respiratory and cardiovascular disease, while nitrogen dioxide is an irritant which increases the severity of asthma and other respiratory diseases) but recent research suggests that, in the USA at least, they are also making people more susceptible to the coronavirus.

Researchers from Harvard University analysed data on PM2.5 levels and COVID-19 deaths from about 3000 US counties covering 98% of the US population. Counties that averaged just one microgram per cubic meter more PM2.5 in the air had a COVID-19 death rate that was 15% higher. This is because the particles penetrate deep into the body, promoting hypertension, heart disease, breathing trouble, and diabetes, all of which make people more susceptible to becoming severely ill with the virus. The particles also weaken the immune system, adding to the risk of getting COVID-19.

As of 24 April, the global death toll from COVID-19 was around 2,700,000. A grim statistic but well short of the 4.2 million lives which, according to the World Health Organization (WHO), are cut short by polluted air every year (not including the large number of deaths linked to indoor air pollution). Here in the UK, a 2016 report commissioned by the NHS estimated that outdoor air pollution is linked to 40,000 deaths annually, twice the current number of coronavirus fatalities. In India, more than a million people die each year as a result of air pollution.

Globally, the WHO estimates that 91% of the population lives in places where air quality falls below acceptable limits.

One of the most remarkable findings during the present crisis was made by Prof Marshall Burke of Stanford University. He used data from US Government sensors in four Chinese cities to measure levels of PM2.5, averaged the drop in pollution levels and calculated the subsequent effect in mortality, scaling this up to give an estimate for the whole of China. Taking a conservative approach, he assumed that there would be no additional deaths in people between 5–70 years old. The study concluded that two months of pollution reduction had saved the lives of between 1400 and 4000 children under 5, and between 51,700–73,000 people over 70.

Altogether, an estimated 20 times more lives were saved by the improvement in air quality than were lost to the virus. This, of course, does not take into account deaths caused by negative consequences of the lockdown such as lack of access to medical services, mental health problems, loss of income, etc.

Improvements across the world


As industrial activity ground to a halt in Hubei Province, the satellite images suddenly changed colour from yellow to blue, indicating a dramatic fall in nitrogen dioxide concentrations. At the same time, energy use fell by 25% leading to a significant drop in carbon dioxide (CO2) emissions.


Satellite images of northern Italy showed the same marked change as the lockdown took effect.


Residents of Indian cities were amazed to glimpse the distant peaks of the Himalayas, no longer obscured by the familiar fog of pollutants. India’s pollution comes from a variety of sources, including the burning of crop residues and dust from construction, as well as traffic, industry and domestic solid fuel burning. Levels of PM2.5 in Delhi during the lockdown plummeted to 20 micrograms per cubic metre, with a 20-day average of 35 — this is a quarter of the normal level.


Los Angeles, infamous for its high levels of atmospheric pollution, was suddenly transformed into one of the world’s cleanest cities as road traffic ground to a halt. Here, both nitrogen dioxide and particulates plummeted because both derive primarily from vehicles.

New York reported similar reductions in pollution: carbon monoxide emissions from vehicles fell by 50%, with CO2 emissions also reducing.


Statistics from the Mayor’s office indicate that levels of nitrogen dioxide at busy junctions may have fallen by 40%, with a 20% drop across the capital. As in the USA, this is due to the reduction in road traffic. Particulates have not fallen dramatically because much of this pollution derives from domestic wood burning.

Could we keep the benefits?

Would it be possible to restart the economy without returning our atmosphere to its former polluted state? Perhaps many of us can identify with Indian politician and author Shashi Tharoor, whose experience of the "blissful sight of blue skies and the joy of breathing clean air” highlights “what we are doing to ourselves the rest of the time”.

The lockdown experience has certainly revealed that dramatic improvements to air quality can be achieved in a matter of weeks and that most urban pollution is locally generated.

Sadly, in China, the pollution levels are already rising to pre-lockdown levels as manufacturing gets underway once more, and this pattern is likely to be followed across the world.

Western nations are already well-aware of the health consequences of poor air quality, hence the existing raft of measures such as ultra-low emission zones, vehicle emission standards and the drive towards electric vehicles. China, too, has cut its air pollution by an estimated 32% over the last six years, although levels remain high. Could some of the forthcoming stimulus to restart the economy be invested in clean technology and renewable energy? Unfortunately, the current plummeting of oil prices decreases the economic incentive to invest in greener alternatives. Electric vehicles are likely to remain beyond the reach of the average motorist, particularly if pump prices drop dramatically and average income falls in the predicted recession. Commentators fear that governments may favour fossil-fuel burning industries, which could be quickly restarted, alongside those sectors which have suffered the greatest job losses such as tourism and hospitality.

The world after coronavirus will be a very different place. To quote motor industry analyst David Leggett of GlobalData, “no-one knows what the role of transport will be when we come out of this, or how cities will work”.


The most realistic hope is that the lockdown experience will lead to a permanent, environmentally beneficial behaviour change, for example, a reduction in air travel and commuting. Hopefully more people will continue to work at home and make use of video conferencing, and walking and cycling every day which they have found to enjoy. As we emerge into a new world, people will have at least some power to decide what they value most and for many, this could be a healthy, clean environment for themselves and the vulnerable members of their community.