Target clean air and carbon emissions together to maximise net zero benefits for ecosystems and health, says Royal Society report

Net zero 'win-wins' which improve air quality while also reducing carbon emissions should be prioritised to maximise the health and environmental benefits of the green transition, a report from the Royal Society has said.

The Effects of Net Zero Policies and Climate Change on Air Quality report, published today, sets out how the changing climate, and the net zero measures adopted to limit further warming, can affect air quality.

In the week that the UK hosts the major international climate summit, COP26, the authors highlight that there are, so far, no equivalent air pollution reduction targets to match the government's "net zero by 2050" pledge. 

Individual climate policies and global warming itself will have a range of effects on pollutant levels, but the UK’s shift to net-zero carbon emissions by 2050 will be net positive for air quality overall, the report says.

Unlike carbon dioxide, many air pollutants persist in the atmosphere for a relatively short time after their source is removed, so prioritising air pollution early in the net-zero transition could quickly translate into healthier lives and ecosystems.

The report’s chair, Professor David Fowler, UK Centre for Ecology and Hydrology, said: "The gases warming our atmosphere and contributing to millions of pollution-linked deaths worldwide share many common sources. We have made strides in cleaning the air of some pollutants, but others, notably particulate matter and ozone, remain a threat to our health and ecosystems. 

"With the COP26 summit focusing attention on the UK’s plans to reach net zero by 2050 -and efforts to get other nations to commit to the same - we should be looking to prioritise measures which also deliver cleaner air. This report makes clear that focusing on these win-wins can ensure the net zero transition also delivers rapid and tangible improvements to our health, our towns and our natural environment."

Each year, air pollution is estimated to account for around seven million premature deaths globally, and more than 28,000 in the UK. 

This report considers five key air pollutants which should be considered in policies on net zero, and air quality: particulate matter, nitrogen dioxide, ozone, ammonia, and volatile organic compounds.

It discusses how climate change will impact air quality, and identifies policies with clear co-benefits for addressing air quality and climate change, including:

• The continued shift away from fossil fuel-powered transport and energy production towards walking, cycling, public transport and electric vehicles leading to lower nitrogen dioxide emissions and particulates
• Changes in red meat consumption and farming practices which could reduce ammonia pollution, from livestock and fertiliser, and methane, a potent greenhouse gas which drives the formation of harmful ozone.
• Conservation and restoration of ecosystems such as peatlands which lock away carbon dioxide, provide ecosystem benefits, and limit future warming-related emissions.

The final chapters discuss possible mitigation measures that could be considered alongside net zero measures to limit negative effects on air quality, including: 

• Using regenerative braking or automation in electric vehicles to reduce the harmful particulates produced by brake and tyre wear
• After-treatment measures to remove particulates emitted through biomass power stations, or volatile chemicals that may be used in carbon capture and storage
• Emissions control measures if hydrogen or biomass boilers become widely adopted, to reduce local impacts of nitric oxide and nitrogen dioxide emissions
• Using ‘low emitting plant species’ - such as beech and lime - in large-scale tree planting and urban environments, or biofuel crops which capture carbon dioxide but limit the release of volatile compounds that can form ozone and other pollutants.

Effects of poor air quality on human health will likely remain despite gradual reductions in exposure to pollutants over coming decades, particularly particulate matter where there is currently no ‘safe’ lower limit. 

The report notes policy priorities, and monitoring of pollution sources, should adapt as the air pollutant mix changes. For example, indoor air quality sensors might be needed to ensure better insulated homes don’t exacerbate indoor air quality issues.

CASE STUDY – METHANE, THE CLIMATE AND AIR QUALITY

Methane is an important greenhouse gas in its own right, 25 times more potent than carbon dioxide in warming the atmosphere. 

In the troposphere – the lowest layer of the Earth’s atmosphere – methane is key to the formation of ozone a gas which can worsen respiratory disease, damage crops, and traps heat – adding to the greenhouse effect.

Human-linked sources of methane are significant, including: fossil fuel extraction, rice farming, and emissions from livestock (which also creates ammonia, another driver of air and environmental pollution).

There are large natural sources as well, high latitude ecosystems, wetlands and tundra in Siberia and Canada, as well as peatlands in Scotland and other parts of northern Europe, respond strongly to global temperatures, as the planet warms they will emit more methane.

Some policies have already helped limit methane emissions and improve air quality, for example, capping landfills that were a major source of methane in the UK, but more work is needed.

"Focusing additional controls on methane addresses both climate change and air quality issues together," said Professor Fowler. “You address global air pollution from ozone as well as reducing climate change, it’s a more powerful greenhouse gas than carbon dioxide, and it hasn’t been targeted very effectively so far.” 

"With livestock being a major contributor, there is also a link back to our diet, and a reduction in red meat could unlock public health benefits, as well as cleaner air and reducing global heating."