The combination of net-zero policies to tackle climate change will accelerate current progress towards clean air in the UK, according to a major new report by the Royal Society.
Encouragingly, according to the report, the options within the range of control measures to achieve net-zero present an opportunity to choose win-wins for climate and clean air and avoid measures which slow the clean-up of the air we breathe.
Here we present a summary of some of its main findings:
Outdoor population exposure and effects of particulate matter (PM) on human health are expected to decline as a result of control measures already enacted and many net-zero policies. However, PM will still pose a significant health risk through to 2050 and effects due to indoor exposures will become more important. Additional efforts to reduce PM will therefore be required.
Effects of ozone (O3) on human health and ecosystems/crop production are expected to remain at similar levels to those of 2020 through to 2050, driven mainly by global O3 background, which in turn depends substantially on natural and anthropogenic methane (CH4) emissions and other O3 precursors, including wildfire emissions. International action to reduce CH4, in combination with national efforts, offer an effective control measure.
In the absence of large reductions in ammonia (NH3) from agriculture, UK emissions of NH3 are expected to grow in response to a warmer climate and will dominate nitrogen deposition and effects on ecosystems and contribute substantially to human health effects through to 2050. Control measures on NH3 emissions at the UK scale would be effective in mitigating this risk.
Emissions and effects of nitrogen dioxide (NO2) on human health in the UK are expected to decline steadily over the next 20 years as a result of net-zero policies and control measures already enacted.
Net-zero measures which may require mitigation to protect air quality
- Combustion of biomass has the potential to lead to reduced net GHG emissions relative to fossil fuels, but could lead to air pollutant emissions, especially particulate matter with a diameter less than 2.5 μm (PM2.5).
- Increased cultivation of fast-growing crops for biofuels may, depending on the land use change, lead to increased biogenic volatile organic compounds (BVOCs) emissions, downwind O3 and secondary organic aerosol formation.
- Use of hydrogen as a combustion fuel has the potential to increase emissions of nitrogen oxides (NOx), a precursor to O3 and PM2.5.
Climate change and air pollution are related issues that merit a co-ordinated policy response. Climate change presents a demonstrable and rapidly growing threat to humanity and nature, while air pollution is estimated to account for around seven million premature deaths per year globally1 and more than 28,000 per year in the UK2.
Greenhouse gases (GHGs) and air pollutants have some common sources, notably the use of fossil fuels for power, transport and heat. Some GHGs contribute to poor air quality, such as CH4, which has contributed substantially to increased O3 in the troposphere. Air pollutants also influence the climate, some having a warming effect (eg O3) and some a cooling effect (eg sulphur). Therefore, many policies to reduce GHG emissions will also benefit air quality and vice versa.
Some GHG reduction measures are more beneficial for air quality than others and these can be selected to address climate change and air quality in the most efficient and economical way. However, there are also sources of air pollutants which do not emit GHGs and hence will not be targeted by climate policies. In these cases, air quality-specific measures are needed to further reduce effects of air pollution on human health and the environment.
Effects of net-zero measures on air quality
The transition to net-zero will deliver significant improvements in air quality as a co-benefit.
The policy challenge is to maximise these improvements while retaining the GHG mitigation. Many of the actions taken to achieve net-zero are unequivocally positive for air quality. In other areas, action can be taken to enhance the air quality benefits, often through small changes.
In a small number of areas, net-zero measures may have adverse impacts on air quality that require mitigation or swapping those measures for others that have no adverse effects on air quality. The short atmospheric lifetimes of most air pollutants mean that positive health benefits start as soon as the source of pollution is removed, providing a rationale for the prioritisation of net-zero measures that also deliver significant air quality co-benefits.
Opportunities with clear co-benefits
- Replacing fossil fuel derived electricity with decarbonised electricity will lead to substantial reductions in emissions of NOx and SO2 and hence in PM2.5 and O3.
- ‘Active travel’ measures that encourage a shift away from car use to walking, cycling and public transport provide both decarbonisation and improvements in air quality, as well as health benefits that extend beyond improving air quality. Reducing demand can decrease emissions that are challenging to address through technology alone, such as non-exhaust PM from road vehicles and aviation jet turbine emissions.
- Improved efficiency in the management of nitrogen in the agricultural system has the potential to reduce NH3, nitrous oxide (N2O) and NOx emissions in most cases. This would feed through into lower concentrations of PM2.5 on a regional scale and a reduction in nitrogen deposition onto ecosystems. Measures to reduce dairy and red meat consumption would reduce NH3 and CH4 emissions, contributing to cleaner air and the net-zero target, as well as benefiting health.
Opportunities to enhance net-zero policies to benefit air quality
A transition to a fully battery electric vehicle fleet should bring significant improvements in urban air quality, benefiting many disadvantaged areas. However, emissions of non-exhaust particles from friction and abrasion such as from tyre, brake and road surface wear, and the resuspension of road dust, will continue to be a significant source of PM2.5 emission, even from a fully electric vehicle fleet.
These emissions could increase if average vehicle mass and numbers were to increase, as it may with larger batteries. This ongoing air quality issue can be mitigated by use of regenerative braking, smoother driving through vehicle autonomy, and the use of new pollution control technologies such as particle capture from brake callipers and low emission tyres.
In addition, one consequence of the reduction in urban NOx emissions is an increase in O3 concentrations because of a reduction in the chemical suppression of O3 that takes place via reaction with nitric oxide (NO). The benefits of NO2 reduction are likely to outweigh any O3 disbenefit at the roadside, but this effect should be recognised, and regional O3 pollution mitigated through policies that also reduce O3 precursor emissions of VOCs.
Net-zero measures that may require mitigation to protect air quality.
The above is an abridged summary of some of the main findings of the report, Effects of net-zero policies and climate change on air quality, produced by the Royal Society. To access the full report click here.