The Uncertain Impacts of Increasing Electric Vehicle use on Air Quality  

13.12.2023 6 min read

The growth of electric vehicles (EVs) in the UK continues to rise as the adoption of EVs becomes increasingly common, with to ban all sales of new petrol and diesel cars by 2035, delayed from the initially set date of 2030. Here we explore in more detail what the uncertain impacts of increasing electric vehicle use could be on air quality.

AS more used electric cars start to enter the market, the falling cost and greater availability means that the electric portion of the UK vehicle fleet is growing exponentially. Registrations of new electric cars grew sevenfold between 2019 and 2022, according to the Society of Motor Manufacturers and Traders (SMMT).

One of the major benefits of electric vehicles for air quality is the absence of an exhaust pipe. Therefore, a whole host of emissions which would have ordinarily been dispersed by conventional internal combustion vehicles are simply not an issue with EVs. Some of these exhaust pollutants and gases include:

  • Carbon dioxide (CO2) – This greenhouse is gas considered to be a major contributor to climate change and ocean acidification.
  • Carbon monoxide (CO) – This gas results from the incomplete combustion of fuel and is toxic to humans. Whilst modern engines typically generate minimal emissions of CO, older engines are a greater concern.
  • Nitrogen oxides (NOx) – Combustion processes also produce nitrogen oxides, which are highly reactive and can have several health consequences from long-term exposure.
  • Sulphur dioxide (SO2) – This is a colourless gas that occurs naturally in crude oil and can cause a range of harmful effects on the lungs.
  • Benzene (C6H6) – Benzene is a carcinogenic substance present in small quantities in petrol and diesel and can be emitted from vehicle exhausts as unburnt fuel. Inhalation can severely harm human health.
  • Particulates – Diesel engines emit tiny airborne particles (typically under <75 microns) of black soot and metal, known as particulate matter. Whilst modern cars are fitted with diesel particulate filters (DPFs) which act to reduce the number of particles emitted, research indicates that there is no safe exposure limit for particulate matter. The smallest particles are the most harmful, as they can easily enter the bloodstream and lead to health consequences such as increased risk of heart attacks and strokes.

Whilst electric vehicles do not generate any of the above emissions from the exhaust, this does not mean that EVs produce no air pollutant emissions at all. Namely, particulate matter emissions are still produced by EVs, but these are generated by tyres and brakes rather than originating from the exhaust pipe.

Given that electric vehicles are typically heavier than their petrol/diesel counterparts due to their large batteries, this puts more strain and wear on the tyres and brakes. The resulting concern is that whilst exhaust emissions are likely to drop off in future years with greater adoption of electric vehicles, non-exhaust particulate matter emissions may not decline in the same way.

This is reflected in the pollutant background concentrations published by the Department of Environment, Food and Rural Affairs (DEFRA), which predicts how background concentrations of various pollutants are expected to change over the forthcoming years. The figure below shows an example of how the predicted concentrations of two of the major pollutants, NOx (largely generated from vehicle exhausts) and PM10 (particulate matter largely generated from vehicle tyres and brakes).

As shown in the above figure, exhaust-generated NOx emissions are predicted to steadily decline between 2020 and 2030, whereas there is only a modest decrease in non-exhaust particulate matter up to around 2025, after which concentrations essentially remain stable. This is partially due to the higher proportion of electric vehicles in the UK fleet leading to a substantial reduction in exhaust emissions but having little effect on the concentrations of non-exhaust pollutants.

The increasing contribution of EV-generated particulate matter emissions is reflected in the London Atmospheric Emissions Inventory (LAEI) data, a tool produced by the Greater London Authority and Transport for London which estimates concentrations of key pollutants within Greater London using an atmospheric dispersion model. The LAEI data for PM10 emissions from different vehicle types in Central London is presented in the figure below, showing how the contribution from the different vehicle types is expected to vary over time.

The LAEI dispersion modelling shows that the contribution of particulate matter emissions from electric vehicles is predicted to rise between 2019 and 2030, whilst the contribution from petrol and diesel vehicles is set to fall over this timeframe. It should be noted that despite the rise in EV emissions during this period, total particulate matter emissions from all three vehicle types are still expected to be reduced in 2030 compared to 2019.

One particular concern with the widespread use of EVs is not only that the concentrations of particulate matter will flatline in the future, but may even worsen as a result – it is argued that the greater wear on the tyres and breaks associated with the heavier weight of these vehicles would lead to higher emissions of non-exhaust particulate matter.

However, these concerns do not necessarily account for certain characteristics of electric vehicles which may help to mitigate these impacts. Firstly, much of the braking in EVs can be done through regenerative braking, where the electric motor works in reverse, converting kinetic energy from the moving vehicle back into electricity,  and re-charging the battery in the process. This means that the use of mechanical brake discs and pads is reduced compared to an internal combustion vehicle.

Additionally, many of the newer EVs are not significantly heavier than their petrol/diesel equivalents, and with the continuous improvements in battery technology, batteries are becoming smaller, lighter and more energy dense. As this trend continues and the typical weight of electric vehicles decreases, we can expect less associated wear on the brakes and tyres, thus leading to a reduction in particulate matter emissions from EVs.

As the challenges relating to air quality continue to evolve over the coming years, environmental consultancies like Temple play a vital role in helping to mitigate and improve air quality in the most affected areas, particularly when it comes to the impacts of road vehicle emissions and the effects of changing rates of electric vehicle use.

The publication of Defra’s Environmental Improvement Plan (2023) establishes a stricter legally binding target and interim target for PM2.5, ultrafine particle matter which forms a significant component of PM10. Despite the potential improvements in EVs and reduction in exhaust emissions from conventional vehicles, the requirement for vehicles to comply with this stricter threshold means air quality issues will remain relevant.

Temple’s in house specialists are able to undertake detailed assessments of these emission sources and identify air quality impacts, taking into account the evolving use of vehicles, as well as offering expert advice to on how developers can appropriately mitigate their impacts on air quality.

Key Contacts

Dr Xiangyu Sheng Director - Air Quality, Climate & Carbon
Zayn Dubois Gafar Consultant