Interview: Professor Alastair Lewis

Air Quality News editor Thomas Barrett spoke to Professor Alastair Lewis from the University of York and chair of the Air Quality Expert Group, about how coronavirus could change air quality forever.

In the earliest weeks of the lockdown in March and April, the University of York’s air pollution department was buzzing with activity. For a scientist studying the data, the event was a once in a career opportunity.

‘It was a very significant event and a one-off,’ says Professor Lewis. ‘It’s an experiment of the kind that we could only ever have simulated with models. If you’re a PhD student working in air pollution you won’t forget it in a hurry.’

But critics might say their efforts were an exercise in stating the obvious: remove cars off the road then the toxic fumes that bellow out of their exhausts will be reduced.

‘People say “so what? Didn’t you expect pollution to go down once you take the cars away?”

‘Well objectively yes, but we never thought we’d see it in real life overnight.’

Professor Lewis says the data is positive reinforcement that their models around cars and nitrogen dioxide (NO2) were accurate.

‘The fact we have a real-world experiment to compare our models against will have a huge amount of scientific and policy value. Even if all its doing is telling us the basic science we already knew about,’ he says.

But whilst NO2 grabbed the headlines, Professor Lewis says there has been more difficulty in trying to spot the difference in particulate matter (PM) because of its complex sources.

‘For many people, it’s a surprise when you take all these cars off the road and you don’t see this high profile pollutant plummet,’ he says.

‘If you reduce cars and change industrial activity then yes you can bring PM2.5 down by 2µg/m3, 3µg/m3, 4µg/m3,’

‘But when you go into the detail you find it’s possibly because it was the whole of Europe who acted. We’ll learn a lot from this.

‘With NO2, the fate is almost in the hands of individual cities,’ says Professor Lewis. ‘Whereas PM2.5 we’ll come away with the conclusion that it’s the contribution of Europe.’

‘There’s a lot to learn there, we’re going into a period where the UK will set its standards on air pollution and the mood music is that they will be stringent ones.’

‘Meeting those targets is a UK owned problem which will rely on European cooperation as well.’

Year zero

Professor Lewis believes there will be parts of the world where the lockdowns will be a very profound event for air quality and citizens will not find it acceptable to move back to business as usual.

Cities in countries like India and Vietnam, which were once blighted with smog, have seen dramatic improvements.

‘The pressure will mount very significantly,’ says Professor Lewis.

‘People have seen the world without it. It will create an enormous amount of pressure to improve things and It will be very hard politically for some places to go backwards.

In the UK, however, it’s sometimes harder to discern whether air quality has improved by that much.

Professor Lewis says the big change we are likely to see here, post-COVID, is that there will be a lot of attention to what are the causes of underlying health conditions.

‘What COVID has flushed out is that unhealthy populations really suffer from these pandemics.’

A proxy

So, what conclusions can be drawn between air pollution and coronavirus?

Professor Lewis wrote a piece in April warning not to be too quick in making easy judgements between the two. He says in some ways air quality has been a victim of its own success because data is so easily accessible.

‘There has been a bit of a rush to look for associations,’ he says. ‘If I want to look at air pollution data for a street in York I can go online and do that. I can’t do the same thing for obesity or smoking. I don’t have access to those data sets and the most accessible data set you can get your hands on is air quality, so it found itself as a proxy for lots of other things.’

‘In a way, it’s a testament to how well organised air pollution data is. It’s probably one of seven or eight factors. Over time more and more analysis will associate these factors but air pollution won’t disappear. ‘

There have also been studies that COVID-19 could be hitching a ride on particulates, which Professor Lewis suggests could be a red herring.

‘It isn’t surprising that you find a virus on particles, that’s not new or unique to COVID. The big uncertainty is how viable the virus is on an ambient particle.’

‘Outside they are exposed to sunlight and oxidants, which are known to kill the virus,’ he adds.

‘The other thing is you need to breathe in a certain dose, and it’s not known what the dose is to inhale to be infected. If you have one or two particles floating around you are almost certainly not going to reach the required dose to get infected.’

‘The idea of returning back to utter gridlock because we’ve opted for cars is highly problematic’

Missed opportunity

As part of Professor Lewis’ role as chair of the Air Quality Expert Group, he organised Defra’s call for evidence on the links between COVID-19 and air pollution, which gathered crucial information from universities, local authorities and private companies on how the pandemic has influenced air quality.

However, with people more or less locked inside their homes for months it revealed one glaring missed opportunity -little has been learnt during the lockdown about indoor air pollution.

‘We hoped someone would come out of the woodwork and the outcome has reaffirmed we have so little data collected on indoor AQ.

‘Many of the questions asked by Defra during this period we simply couldn’t answer, as we just don’t collect the relevant information. It was however reassuring that we connected together all these changes in outdoor air pollution.’


In a period of darkness, with tens of thousands of people losing their lives to the virus, people have taken hope from the reduction in air pollution.

Professor Lewis hopes that this won’t be false hope.

‘The idea of returning back to utter gridlock because we’ve opted for cars is highly problematic,’ he says.

‘There’s a problem that people can’t always envisage what something could be like — now we’ve had this chance to experience a major change. Smart cities will look on this as an opportunity. The public mood is not ‘let’s get back to high air pollution as quickly as we can’ when people have seen what the city can be like when it’s not gridlocked with cars.’

This article first appeared in the July issue of the Air Quality News magazine, which you can read here.




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