Air Pollution, Covid, and what we can do to change it

Covid-19 is a respiratory disease. The suggestion that our polluted modern air contributed to severity of the pandemic, on the face of it, sounds plausible.

According to the WHO outdoor air pollution kills approximately 4.2 million people every year. These deaths are caused by ‘increased mortality from stroke, heart disease, chronic obstructive pulmonary disease, lung cancer and acute respiratory infections.’ Covid is an acute respiratory infection – therefore our polluted cities are bound to be a factor.

As an aside, to put this into context, at time of writing, the world death toll for covid has not yet passed 1.5million. If we could save 4.2million lives a year as well as making a serious dent in that 1.5million who have died from the acute respiratory infection that is covid – what are we waiting for?

Some more concrete figures to base our decision upon? As of this autumn 2020 the evidence is becoming a lot clearer.

Recently this excellent paper was published on the topic of ambient (ie outdoor) air pollution and covid. It serves not only as a great study into the link between air pollution and covid outcomes in the UK but also as a summary of evidence so far.

The Pollutants they Looked at Were:

  • Particulate Matter
  • Nitrogen Oxide
  • Nitrogen Dioxide
  • Ozone

Particulate Matter
They sound like something out of Star Trek right? But they’re real and we breathe them every day. They are usually classified as PM2.5 (particulate matter smaller than 2.5μm) and PM10 (particulate matter smaller than 10μm). For the lay people among you (me included) – a μm is really really small…

PM2.5 is particles from soot, tobacco smoke, smog etc as well as biological hazards like virusses and cat allergens.

PM10 means larger particles like mold spores, ash, cement dust, oil smoke and some bacteria.

This wikipedia quote says it best: Overall, ambient particulate matter ranks as the sixth leading risk factor for premature death globally.

Nitrogen Dioxide

Nitrogen Dioxide is formed when Oxygen in the air combines with Nitrogen from fuel combustion (ie cars etc).

-Nitrogen Dioxide reacts with other particles to form PM2.5s (see above)
-It is also dangerous in and of itself in high concentrations. There is a strong association with worsening symptoms of asthma as well as less well established associations with other non-respiratory conditions such as heart disease, diabetes and all cause mortality.
-It reacts with VOCs (volatile organic compounds) to make ozone. Ozone has some really nasty health risks damaging your lung tissue.

Nitrogen Monoxide

Although less harmful in itself than Nitrogen Dioxide, it is a precursor to Nitrogen Dioxide. ie it reacts with other substances to make Nitrogen Dioxide.

Interestingly Nitrogen Monoxide can react during the night with Ozone to make Nitrogen Dioxide AND oxygen. So it is what is called a ‘scavenger’ of Ozone.

It is worth noting that Nitrogen Monoxide also contributes to acid rain and ozone layer depletion (and hence to manmade climate change). So it’s better to have less of it around.


Again wikipedia says it best:
Hundreds of studies suggest that ozone is harmful to people at levels currently found in urban areas. Ozone has been shown to affect the respiratory, cardiovascular and central nervous system. Early death and problems in reproductive health and development are also shown to be associated with ozone exposure.

The more you look into ozone the more horror stories you’ll find. As stated above, the pollution in urban areas comes from a reaction between volatile organic compounds and Nitrogen Dioxide.


So the study I referred to at the start of this article looked at the relationship between the quantity of particles (detailed above!) in a locality and the covid cases/outcomes of people living there.

The data sets they looked at were from the UK – the ONS (office of national statistics in the UK) and the EEA (European Environmental Agency). They used local authority data as well as UK Biobank data. (UK BioBank is a UK government initiative tracking a large number of individuals for health/environmental factors vs outcomes)

They made an effort to take some confounding variables out of the equation such as income, population density and median age of the localities they looked at. In other words, by the time they’d crunched the numbers, hopefully these factors didn’t skew the relationship we are looking at. (ie pollution <-> covid outcomes)

What the researchers found was a strong relationship between higher levels of both Nitrogen Dioxide and Nitrogen Monoxide and worse covid outcomes (ie both case numbers and deaths).

Interestingy, they didn’t see any relationship with PM2.5 and PM10 and covid until they looked at the BioBank data which is much more precise in terms of location (ie they had access to the location of participants’ homes rather than just the local authority data just giving them a town location). Then suddenly there was a relationship between particulate matter and covid outcomes.

The implication here is that if you live next to a factory or a busy road or people are pumping out smog from wood fires etc then it matters that you actually live next to it. Just living in the same county wouldn’t make any difference. Whereas with Nitrogen Oxides (dioxide or monoxide) the problem is more diffuse over a large area.

Ozone was more complicated – it showed a negative relationship – ie the higher the levels of ozone, the better your covid outcome. Yes you did just read that right. Sadly this doesn’t mean ozone is some miracle cure… They tried to explain this by the fact that Nitrogen Monoxide is a scavenger of Ozone.

Remember I said Nitrogen Monoxide reacts with ozone to make nitrogen dioxide and oxygen? Well the moment you have significantly higher levels of Nitrogen Monoxide in an area (lets say from car exhausts in a city), you’ll have a significant scavenger of Ozone. So although levels may increase dramatically during the daytime, they’ll go down at night – likely to lower levels than you would have in a rural area.

Thus Ozone, though a damaging pollutant is often going to be present in higher levels in areas that are LESS polluted with Nitrogen Oxides. (because the ozone is cleaned up in the more highly nitrogen oxide polluted areas). Therefore there would be less Nitrogen Oxide in those areas causing bad covid outcomes. Therefore the mild inverse relationship with covid mortality.

All this serves to show just how complicated a study into pollution vs covid cases can get. That said, the results seem very clear at this point. Air pollution was a major factor in the severity of this covid-19 pandemic.

This study also gives a pretty good summary of the research to date – of which there is plenty. Elsewhere there is a lot of evidence related to Northern Italy, China, comparisons between the UK and the rest of europe etc that point towards air pollution being a major factor in our susceptibility to covid-19. As a society we would do well to take note and change our behaviour.

What do we do?

The European Environmental Agency states the following as the list of major air pollution:

  • burning of fossil fuels in electricity generation, transport, industry and households;
  • industrial processes and solvent use, for example in the chemical and mining industries;
  • agriculture;
  • waste treatment;
  • natural sources, including volcanic eruptions, windblown dust, sea-salt spray and emissions of volatile organic compounds from plants

All but the last one we can control. We can:

  • use less energy in our homes – use light and heat only where we need it – not just out of habit.
  • use cars/air travel less and instead use feet, bikes and trains more
  • buy food from sources that use regenerative agriculture locally rather than high energy, high intensity farms that require the goods be transported long distances

The problem we face both as individuals and for government and businesses to tackle is that it is a large number of small measures that will make the difference.

If you tell people they have to stay in mostly for 3 months in winter and wear a mask when they shop for food they get it instantly. It’s simple and by and large it works.

But changing the way we live to improve the quality of our air requires every one of us individually to be creative about our daily habits and find ways to reduce our polluting impact on many fronts.

However difficult this seems, the incentive is there. The list of solutions I have provided above would all be helpful in fighting pandemic disease, not just on the level of air pollution reduction but also in getting us more exercise, getting us better food and not spreading the virus so fast by travelling less. The list is also strikingly similar to one that would help us fight climate change.

How long will it be before we prioritise having clean air to breathe as a way to save lives from covid and many other killer diseases?

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