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Pandemic Lockdown Gives Preview of Attainable Air Quality

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Take a look at these videos of Italy and China made with data from the Copernicus Sentinel-5P satellite data during the recent lockdown period. Striking isn’t it how rapidly and markedly the harmful compounds polluting our atmosphere drop off when humanity grinds to a halt. It also serves to highlight just how much our industrialized areas contribute to air pollution problems.

Air pollution from nitrogen dioxide emissions is declining over Italy according to Copernicus Sentinel-5P satellite data from Jan. 1-Mar. 11, 2020

A drop in nitrogen dioxide emissions correlated to the nationwide quarantine in China in January 2020. Two months later the emissions are increasing.

How is air pollution looking in a locked-down world?

These data highlight the drop in nitrogen dioxide (NO2) levels, but industry and the movement of people around the world also pumps out other environment-damaging gasses, such as sulphur dioxide (SO2) and ozone (O3), and harmful particulates. Here too the picture is likely to be similar.

Prof William Collins, Professor of Meteorology at University of Reading, said “A large amount of the air pollution we breathe comes from traffic. With many countries on lockdown the levels of traffic pollution have plummeted. Satellites have picked up very large decreases in levels of NO2 (primarily from diesels) in all industrial regions of the world. We expect fine particulate matter (PM) has similarly reduced.”

As you can see from the simulations above, Wuhan in China (one of the most polluted cities in one of the most polluted countries) and northern Italy (one of the most polluted areas in Europe) saw vast drops in air pollution, a scenario echoed elsewhere. In London and the suburbs, NO2 and particulates measured at roadside monitoring stations are noticeably lower for the time of year.

Might improved air quality translate to air pollution-related mortality reductions?

Air pollution is attributed to the deaths of seven million people globally each year, 4.2 million of those from ambient (outdoor) air pollution. It also contributes to poor health, causing or exacerbating conditions such as asthma and cardiovascular disease, and has been linked to cancers, adverse birth outcomes and even cognitive issues.

Prof Anna Hansell, Professor in Environmental Epidemiology at the University of Leicester, commented “The Committee on Medical Effects of Air Pollutants have reviewed evidence on PM2.5 (fine particulates) and NO2 in the past two years. It found that each annual average 10 microgram/m3 increase in PM2.5 is associated with an increase of 6% in mortality and each 10 microgram/m3 increase in annual average NO2 with an increase of 2.3% in mortality.”

People may be exposed to harmful ambient air pollution by a number of means. This may be through their line of work, the areas in which they live or even the methods of exercise or commuting they adopt. Cycling, running or walking in traffic-filled streets inevitably exposes people to more pollutants than sitting in an air-conditioned car or walking in the countryside for example. Lockdown has not only reduced industrial emissions but also traffic emissions – good news for those living in congested areas. Whilst many of us are no longer commuting (on foot or by vehicle), for those able to get out into the fresh air for some exercise, it means cleaner air to breath too.

Whilst it is nigh on impossible to avoid the growing figures of sad deaths that have been caused by COVID-19, what about those deaths avoided by the linked reduction of air pollution?

Prof Collins continued “Big reductions in exposure to pollutants will also have come because people are no longer walking on the streets. It is too early to say whether these improvements will offset any of the mortality from COVID-19, or other health problems due to be confined indoors.”

Prof Hansell added “Sadly we may not see reductions in air pollution translated into direct drops in mortality. In fact, it will be very difficult to interpret mortality trends in 2020-2021 – there will be an increase in numbers of deaths due to COVID-19 but also impacts of financial hardship and stress (we know that poverty increases risk and severity of chronic diseases and also death rates), adverse impacts of isolation of the elderly (impacting on their health in various ways) and impact of restrictions on access to healthcare for non-COVID-19 diseases. The latter three are likely to have knock-on effects on mortality for several years after the pandemic. On the plus side there should be reduced transmission of various infections at least in 2020-21 from social distancing, leading to reductions in deaths from infectious disease such as non-COVID-19 pneumonia (currently 25-30,000 deaths per year in England).

Considering the high levels of pollution in Wuhan and Northern Italy, two of the areas worst hit by COVID-19, some have suggested that the two things are linked. Could living in an area with poor air quality have put residents at higher risk of contracting respiratory infections and worsen clinical signs? “It is interesting to speculate whether air pollution in Wuhan and Italy areas may have had an impact on susceptibility to the virus, either directly affecting infection rates or indirectly affecting severity (via contributions to increased heart and lung disease that put you at greater risk of severe COVID-19 disease) – it’s an area that needs further research” concluded Prof Hansell.

Lasting lessons for the future?

Whilst the current reductions in air pollution stem from enforced measures, it provides us with a snapshot of the air quality that can be achieved when the burden of anthropogenic activity is removed. Whilst no-one is suggesting that this is a permanent solution to our air quality woes, it does provide scientists with insightful data on the effects of reduced emissions.

Prof Alastair Lewis, Professor of Atmospheric Chemistry, National Centre for Atmospheric Science, University of York, commented “The temporary reductions in emissions being seen at the moment provide us with some unique insight into what might be possible for future air quality in cities. The large reductions being seen in transport emissions of NOx allow us to evaluate how the atmosphere will respond to a future electrified fleet that will no longer emit this pollutant. The chemistry of the atmosphere is complex with many contributing sources, and this “clean” period is likely to help in inform what air quality standards might be feasible for secondary pollutants such as PM2.5 and ozone in the future.”

Looking to the future, Prof Jonathan Grigg, Professor of Paediatric Respiratory and Environmental Medicine, Queen Mary University of London (QMUL), concluded “During the pandemic, staying indoors and reduced road emissions will protect vulnerable people from the adverse effects of air pollution. When the pandemic is over it should be possible to assess this using routinely collected NHS data. I hope that after the lock down has ended, we can move into a cleaner breathed environment, and one where we are more aware about protecting vulnerable people from respiratory virus infections.”