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I'm reading: The air we breathe

More than 90 per cent of people living in urban areas are exposed to air pollution levels that exceed World Health Organization (WHO) limits. Outdoor air pollution is one of the largest causes of deaths worldwide, claiming more than four million lives per year, including almost a quarter of all stroke deaths and 29 per cent of all disease and deaths from lung cancer, according to WHO figures.


The statistics are stark, and evidence of the problem is mounting daily. Monitoring stations in cities around the world are collecting reams of data around the clock, yet sorting through the information and putting it to good, practical use is a tricky task.

This is exactly what Professor Dominick Spracklen’s team does in the School of Earth and Environment. The UK’s air pollution issues “pale in comparison” with other regions in the world, he says. Using pollution data and complex computer models, he is on a mission to understand the “bigger problems” faced by countries including China and India.


Dominick is “passionate about trying to use scientific understanding to inform decision makers so that they can craft better policies to improve air quality.”

He really hopes to make a difference in India, where pollution is off the scale and getting worse. 14 Indian cities are amongst the 20 most polluted in the world, according to WHO data. Last year, a public health emergency was declared in Delhi as pollution levels exceeded 70 times the safe limit.


The city ranking is based on levels of particles under 2.5 microns in size (PM2.5), measured in micrograms per cubic metre of air. The particles, 20–30 times smaller than the width of a human hair, are known to increase the likelihood of respiratory and cardiovascular diseases.


Dominick’s team revealed that India’s most serious pollution problem is caused by people burning solid fuels in the home for cooking and heat. “There are millions of people burning wood and charcoal in their homes, and that aggregates to be a really big pollution source,” he says.


“That sort of information needs to be understood if you are trying to sort out air pollution issues because the solutions that might have worked in the UK and Europe are not transferable directly to India,” he adds. “Getting Delhi’s cars to meet European emissions standards isn’t going to solve the problem on its own, when most of the pollution comes from other sources.”

The global picture

The global picture is complex, as can be seen when looking at the different contributors to poor air quality in different countries.


In China the greatest contributor is industry (43%). Residential activity contributes 38%, while other sources (including power, transport and fires) make up 19%.


In India, the picture is different, with residential activity accounting for 51%, power generation 20.75% and other causes 28.25%.

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Luke Conibear is a PhD student in Dominick’s group. He has used computer models and local measurements to study the impacts of air pollution on human health. “One million premature deaths are attributable to ambient air pollution exposure in India alone each year,” he says.


The team used advanced modelling to study the disease burden due to PM2.5 exposure in India. They focused on seven different types of emission sources, from industrial power plants to transport and home energy use. Using their models, they found that preventing emissions from home fires gives the largest reduction in ambient PM2.5 exposure.


However, solving the air pollution crisis is not that simple. Their calculations also suggest that reducing emissions may provide fewer health benefits than expected, at least initially. “In general, air needs to be really clean for good health. As air quality gets worse, the effect on health increases sharply and then flattens off at really high levels. This is because the cardiovascular system is very sensitive to low levels of air pollutants,” explains Luke. He likens it to smoking, where there is a substantial increase in health risk with the first cigarette, while the change in risk is relatively smaller for the thirtieth. This means that India will have to make really deep cuts in pollutant emissions before large benefits to health will be realised.

Until a few years ago, Indian pollution data was extremely hard to come by. The country still doesn’t publish as much data as China, which now has a very well-established air quality community. The Chinese government has taken action to cut pollution levels, for example by banning people from burning coal in their homes, and closing some of the most polluting power plants. It now publishes daily pollution data from monitoring stations across the country.


Most studies of recent trends in air pollution across China have used satellite data, which suggest that levels of sulphur dioxide, nitrogen dioxide and PM2.5 have all begun to decrease. But there have been few attempts to use data from the surface monitoring stations to assess recent trends.


In a project funded by AIA, the pan-Asian life insurance group, Dominick’s team has used data collected at over 1,600 surface monitoring stations between 2015 and 2017.


“Because things are changing so rapidly in China, even over that very short period we could see a deep reduction in PM2.5, showing that particulate pollution has got quite a lot better,” says Ben Silver, the PhD student who led the work. But with weather playing a key role in air pollution, the researchers are cautious in their interpretations.

"We were able to demonstrate that slowing deforestation has saved thousands of lives a year through improved air quality. That’s an important public health benefit that no one had really expected."

What can we do?

The research also indicates that levels of ozone, another pollutant dangerous to health, appear to be creeping up, although the reasons why are not clear. “The next bit of work we are planning is to use our model to try to unpick what has happened over the last few years,” says Dominick.


Ben is now working on climate mitigation policies, using a model to simulate how different strategies might alter air quality. “There might be big win-win scenarios where carbon emissions can be reduced and air pollution improved at the same time. We want to help identify those strategies,” he says.


In Brazil, Dominick focuses on deforestation and fires. Combining satellite data with complex computer models, he analysed connections between deforestation and air pollution. The fires are used to clear forests to make way for agriculture, but they cause “very strong pollution events,” he says.


“Brazil had achieved large reductions in deforestation rate and we wanted to see whether there was an impact on air quality, which no one had really looked at before. Amazingly, we found that as deforestation declined, air quality improved. We were able to demonstrate that slowing deforestation has saved thousands of lives a year through improved air quality. That’s an important public health benefit that no one had really expected.”

In a new project in Indonesia, he is also studying the harmful effects of fires used to clear vegetation, often to make way for palm oil plantations. To make matters more complex, a lot of the land is peat-based. As the UK witnessed with this summer’s Saddleworth Moor fires, if the peat dries out, it burns frighteningly well. In some Indonesian forests, the peat layers can be metres thick and the fire can burn down 50 centimetres or more, releasing an “incredible amount of pollution into the atmosphere,” he says.


Dominick has set up a collaboration with Bogor Agricultural University with the aim of understanding how land-use change, fire, peat and pollution all link to each other. The Bogor experts are computer scientists who use detailed data mining techniques. He also has a five-year grant from the European Research Council (ERC) to work on the climate and air quality impacts of tropical deforestation.

“It’s becoming increasingly clear that deforestation causes local climate change,” says Dominick. He estimates that “local increases in temperature due to deforestation could be as large as the increases that are due to global increases in carbon dioxide.


“In forests, energy from the sun is used to evaporate moisture rather than heating up the local land surface,” he explains. “But if you clear the forest you stop that process and so a lot more energy just goes to heating the surface.”


Not only does clearing the forest cause a significant increase in local temperature, it can also affect local rainfall, he adds. Some non-governmental organisations are particularly “excited” by the deforestation findings and plan to use them to help persuade policy makers to see the benefit of protecting forests.

One NGO, the World Land Trust, even funds a PhD student in Dominick’s group to research a forest conservation area in Vietnam.


Dominick’s work would simply not be possible without collaborations with other researchers, both at Leeds and across the world. “As much as possible, we always try to collaborate with local institutions. For example, for a lot of the work that we are doing in China, we are working closely with researchers from a number of Chinese universities and so hopefully, as we get the results, we will work with those partners to communicate to relevant stakeholders,” he says.


He finds his work highly satisfying. “The really exciting thing is making new discoveries, in making that addition to our scientific understanding. I really enjoy the fundamental aspect, improving our knowledge of air pollution and of interactions between different parts of the system – air pollution, human activity, and land-use change.”


He appreciates that policy makers have a difficult job. “We might say that to improve air quality in Indonesia we need to reduce fires on peatlands. But how a policymaker actually tries to make that happen in practice is a very complex thing to do. Science needs not just to identify problems but also workable solutions.”

Measuring air quality on campus

The University of Leeds Living Lab for Air Quality launched in November 2017 and aims to help shape and inform the University’s plan to limit exposure to poor air quality.


The Lab is running a monitoring programme gathering, analysing and mapping air quality in and around campus. The data collected is uploaded to the website of The Centre of Excellence for Modelling the Atmosphere and Climate (CEMAC) so that it is accessible to staff, students and those external to the University for research and teaching purposes, and for wider interest.


The University is currently working with Leeds City Council to scale the project out to different areas of the city, and is sharing our progress and learning with colleagues at Shanghai Jaio Tong University and the University of Nairobi.


The Living Lab is a collaboration between the Sustainability Service, the School of Earth and Environment, the Institute for Climate & Atmospheric Science (ICAS), the Institute for Transport Studies and the School of Civil Engineering.

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