Professor of atmospheric chemistry at the University of York and a director of the National Centre for Atmospheric Science in the UK, Alastair Lewis is a leading international figure in fighting air pollution across the world.
Increased transportation of people and goods leads to more fossil fuel-based emissions, and even the provision of more food leads to emissions and air pollution.
Professor of atmospheric chemistry at the University of York and a director of the National Centre for Atmospheric Science in the UK, Alastair Lewis is a leading international figure in fighting air pollution across the world. Currently chair of the UK government’s science advisory group on air pollution, he has been working with scientists in India the past five years to create new measurements of emissions for Delhi. Lewis, who was a speaker at this year’s Jaipur Literature Festival, spoke with Faizal Khan about the science of air pollution and his work in India. Edited excerpts:
How different and dangerous is our atmosphere today compared to the last century? It’s a complex answer to a simple-sounding question. In short, it depends very much on where you are in the world. In some locations, notably Europe, North America and Japan, air quality in 2021 is much better than it was 50 or 100 years ago, the product of more than a century of emissions controls, gradual de-industrialisation and decarbonisation of the energy supply. However, for perhaps the majority of the world population, air pollution has gotten worse compared to 50 or 100 years ago. Lots of reasons lie behind this: rapid growth in population, expansion in economies, industrialisation replacing agriculture as a dominant part of economies and increased standard of living are all drivers of increased pollution. In terms of danger, this is a difficult one to answer. The toxicity of air pollution has certainly changed over the last 50-100 years.
What are the major factors that have contributed to the deterioration of earth’s atmosphere? There is a difficult balancing act to manage, something which has played out over centuries, which is how do you grow economies and improve standards of living without going through a period of poor air quality as a consequence? Providing affordable access to electrical power and heat for homes and cooking has, in the past, meant burning fossil fuels, and coal has historically been a very cheap way to do this (although this is changing rapidly). Increased transportation of people and goods leads to more fossil fuel-based emissions, and even the provision of more food leads to emissions and air pollution. There are now solutions to many of these problems, but they often still cost more than the older polluting versions, and the demand for economic growth has often taken precedence.
How do you explain the vast differences in air quality of places like Delhi and London? The first point that is often overlooked is geography. Even if London and Delhi had identical emissions per person, London would probably do better on average. The UK is a small island on the edge of a very windy and wet Atlantic ocean with very little in the way of upwind emitters for thousands of kilometres. Delhi is surrounded by a large land mass and has climatic conditions in winter that can lead to severe build-up of pollution. Of course, that isn’t the only reason. London has been grappling with air pollution since the early 1800s and was, for many years, probably the most polluted city on earth. It is now almost completely de-industrialised and has seen implementation of ever more stringent air quality controls, and in the wider UK, since the 1960s. Delhi currently has substantial emissions coming from within the city itself, but it’s also affected by the wider NCR, and indeed the country beyond that. The process of controlling and reducing air pollution in India has only been running in earnest for a couple of decades, so is in its early phases. The key challenge for India and Delhi is to pass through this polluted transition as quickly as possible. London was terribly polluted for perhaps 150 years. The question is whether Delhi can fix its pollution problems much quicker than that.
Is there enough international collaboration on air pollution and setting standards and limits? There is excellent international collaboration on research into atmospheric chemistry and air pollution, and an open environment of sharing knowledge. Often, this is very hands-on international cooperation on measuring pollution in the field, sharing advanced instruments for studying pollution and developing models. In the last five years, I’ve been involved in large collaborative projects between the UK and Chinese scientists on measurements in Beijing, and with Indian scientists, working together in Delhi.
You have mentioned working with Indian scientists in Delhi. Would you elaborate on the collaboration? There have been some large India-UK collaborative experiments on air pollution in the last couple of years. My own institution, University of York-along with Universities of Manchester and Birmingham-have been working with IIT-Roorkee, IIT-Kanpur, CSIR-National Physical Laboratory, Indira Gandhi Delhi Technical University for Women and National Environmental Engineering Research Institute, Nagpur. This has involved bringing equipment from the UK to India to join with equipment already in India to make new measurements of atmospheric composition, of pollution emissions (for example, from vehicles) and to improve modelled estimates of emissions for official inventories.
How advanced is scientific research into air pollution today? Are there things we don’t know yet? The major challenge is ensuring that we keep track of how the chemistry of pollution changes as pollution sources change, and that we are confident that we can design solutions that work well for the place they’re going to be implemented. In the 1960s in the UK, pollution chemistry was dominated by sulfur from the burning of coal in power stations and homes. That needed research to understand those processes. But coal burning has virtually disappeared in the UK, to be replaced by processes linked to vehicles and agriculture instead. The chemistry that produced photochemical smog (which is predominantly low-level ozone) used to be dominated by the chemistry of gasoline vapour and car exhaust, but now, it is controlled by chemicals from commercial solvents and household products. So air pollution is a moving target and ensuring our scientific knowledge keeps up with present-day (and future) emissions is key.
Vehicular pollution is often cited as the major reason for air pollution in Indian cities. How does it hold against science and data? It’s not just Indian cities… around the world, vehicles are probably the most clearly identifiable source of urban air pollution. They are, of course, very important, and this includes not just pollutants that come from the tailpipe, but also from the wear of tyres and brakes, and the agitation of the road surface. But there is a risk that sometimes too much attention gets paid to this one very visible source. The harmful effects of nitrogen oxides from vehicles combine with agricultural emissions of ammonia to form harmful particulate matter (sometimes called PM2.5). Only tackling polluting vehicles wouldn’t solve the problem, it needs policies that reduce emissions from multiple sectors simultaneously. Having said that, Delhi does still operate with a large proportion of high-emitting vehicles and so there is a lot that can be done to reduce emissions.
During the lockdown last year, people in Punjab could see the Himalayan peaks over 100 km away. How has coronavirus impacted air pollution? In some places, the reduction in travel and industrial output has had a significant impact on air pollution. It hasn’t been universal, but some of the imagery of improved visibility that came out of India was the most dramatic anywhere in the world. The pandemic has shown how the atmosphere responds to large changes in emissions, and that the effects and benefits can occur very rapidly. The biggest sector affected by the pandemic was transportation, and so those locations where transport made up a large fraction of air pollution saw the largest improvements— India being one of those places. The pandemic has seen considerable social engagement with the issue of air quality, and it has been an encouragement in some badly affected countries to do more, because for the first time, a world without poor air quality has been visible. Having said that, in countries like the UK, reductions in some pollutants were rather small because road transport is no longer such a dominant source of pollution.
You have criticised air filtration methods like smog towers in the past. Are domestic air purifiers any different? They can make a positive difference for particulate matter, especially if you live in a badly polluted location. If I lived in Delhi, I would probably own an air filtration system for my home. But they aren’t an equitable or sustainable solution. They move responsibility for good air quality away from the polluter and on to the individual family, leaving them to clean up the air in their own home even if they didn’t pollute it. This introduces a whole set of inequalities into the provision of clean air. If you have the resources, you can buy your way around the problem. Up until recently, air pollution has been a great leveller. No matter whether you were rich or poor, we all breathed the same air, and that was a powerful motivation for action at the civic level. There are also a whole bunch of other unsustainable aspects about filtration like the materials to feed them with electricity and filters and so on, and I have some concerns about how the disposal of billions of filters in landfill might play out over time.