What the UK’s first lockdown taught us about air quality

With England in the midst of its second national lockdown, and with the rest of the UK under tight restrictions in an effort to control the spread of COVID-19, we need to learn from the changes we saw happening in March, writes Mark Nichols.

Mark Nichols is an air quality engineer at the multi-disciplinary firm, Hydrock, and co-author of the report: Changes in ambient air quality and atmospheric composition and reactivity in the South East of the UK as a result of the COVID-19 lockdown.

The research paper was led by Dr Kevin Wyche of the University of Brighton’s ‘Air Environment Research’ group and was published in the journal, Science of the Total Environment (STOTEN).

Air quality during lockdown cannot be taken at face value

In the early days of the pandemic, news reports focused on the benefits that the fall in vehicle traffic was having on air quality.

However, this doesn’t recognise the hidden rise in toxic air pollution that occurred as a result of the knock-on effect in changes to atmospheric composition.

The increase in pollutants such as ozone (O3) could be more harmful and a greater risk to human health, particularly while the world is vulnerable to a deadly respiratory virus.

We should not be lauding lockdown as a panacea, instead, we need to understand air quality as a whole to help governments and businesses form a proper, nuanced response to tackle air pollution.

To date, policy interventions have focused on reducing vehicle tailpipe emissions, but our research shows that these could be too simplistic, blunt instruments which may have unintended, harmful consequences.

A complex picture: a rise in toxic pollutants

Acting on behalf of DEFRA, the research paper was borne out of the Air Quality Expert Group’s (AQEG) call for rapid evidence. The objective was to assess changes in air pollution emissions, concentrations and exposure during the COVID-19 outbreak in the UK.

The lockdown period provided a unique opportunity to assess the atmospheric response given the volume of traffic fell to levels last seen in the 1950s, declining by as much as 70%-80%.

The south-east was chosen for the study as it has the largest regional population of approximately 9.13 million and is geographically located between two major air pollution hotspots (London and north-western Europe).

Using data collected from the UK’s national network of air pollution monitoring stations, the research showed that over the March — June 2020 period, nitrogen dioxide (NO2) concentrations fell by between 14% and 38% compared to the preceding five-year baseline for the same period owing to a significant decrease in vehicle movements.

As a consequence, there was a clear change in atmospheric composition and reactivity during lockdown, resulting in a shift in the public’s exposure to different pollutants. NOx (NO + NO2) and O3 lie in chemical balance in the atmosphere, which means that if you disturb one, you alter the other.

As a result of the rapid decline of NOx, the atmosphere became more reactive, and we saw an increase in ground-level ozone above what would be expected during the abnormal sunny weather that predominated much of the first lockdown.

This means that the atmosphere in urban locations shifted to a ‘hydrocarbon limited ozone production regime’ whereby NOx declined but non-methane hydrocarbons (NMHCs) prevailed and this allowed ozone production to increase with concentrations up by as much as 15%.

Emissions of NMHC’s are associated with industrial output, and many industries, such as manufacturing, continued to operate throughout lockdown as ‘essential business’.

This goes some way to explain why these emissions did not fall as rapidly as NO2 and underlines the need to understand air pollution as a whole, rather than solely focusing on the impact of vehicle emissions.

A more reactive atmosphere also has the potential to increase our exposure to pollutants such as Ultra Fine Particulate Matter (UFPs).

These can form by volatile compounds reacting with ozone in the atmosphere — further contributing to this complex and toxic air quality picture that we observed during the first lockdown.

Lockdown increasing risk to human health?

Air pollution is one of the single biggest ongoing threats facing global public health today and our research has shown that ‘air quality’ and ‘air pollution’ are not standard, linear measures and cannot be approached simply.

The adverse health effects of acute and chronic exposure to poor air quality — most commonly linked to vehicle emissions — are well known, with links to premature deaths, significantly exacerbated respiratory problems such as asthma, cardiovascular diseases, diabetes, airway oxidative stress and dementia.

However, there is evidence that O3 exposure can cause greater lung damage than NO2 at comparable concentrations.

This suggests that ozone is a more harmful pollutant to human health, and with our research showing an increase in O3 over the first lockdown period, it is imperative that we understand the changes occurring within our atmosphere and what this means in terms of potentially increasing people’s health risk.

Given the current pandemic, now more than ever we particularly need to understand the impacts of major respiratory air pollutants. There is emerging evidence which shows that these can exacerbate the effects of respiratory diseases such as COVID-19, and pollutants could possibly act as vectors for these viruses and worsen their spread.

This is why it is vital that we learn from the scientific body of research that has emerged out of the first lockdown and we urge caution with overly simplistic statements about the positive effects of lockdown on air quality and, as a result, health.

Shaping the policy of the future

While a decline in vehicle emissions is positive in many ways, our research shows the decrease in NO2 caused a host of unintended consequences.

In effect, lockdown gave us the opportunity to conduct real-world simulations of the potential impact of policy interventions that aim to move us to a greener future. Many policies typically focus on reducing tailpipe emissions, for example by incentivising the use of electric vehicles and introducing clean air zones and congestion charges.

But as we have shown, without due consideration to pollutants from other sectors, these measures will only go so far and might in fact, inadvertently be resulting in changes to air quality composition that is just as bad, if not worse, for human health.

Policy-makers need to understand that when we talk about ‘air quality’, it cannot solely be about NO2 emissions from vehicles.

Emissions need to be looked at in the round and it should be recognised that there are many substances that we breathe which come from a variety of sources. Unless these are looked at and addressed holistically, we are in danger of causing atmospheric imbalances that trigger changes in its reactivity and cause a hidden rise in toxic air pollutants.

At a time when the nation needs to be doing all it can to protect people’s health, by not tackling air quality properly, we could be addressing one problem, while simultaneously exacerbating another.

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