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Do electric vehicles reduce air pollution?
Electric cars improve air quality compared to petrol and diesel cars, but they do not completely fix the problem.
One of the touted benefits of electric vehicles is that they reduce local air pollution. They’re not just better for the climate, they clean up our air too.
But there have been question marks around this assumption. There might be no tailpipe emissions from an electric vehicle (EV) but if they’re heavier – which the average one currently is – there could be more pollution from brake, tyre, and road wear. Would this be enough to undo the benefits of having no exhaust emissions?
In this post, I’ll give an overview of what the research says (and doesn’t yet know).
Here’s a brief summary of the take-homes:
Overall, electric cars do reduce levels of air pollution compared to petrol, and especially diesel cars.
The size of this reduction depends on their weight, the age and type of car they’re replacing, and the electricity mix.
Electric cars do not completely fix the problem. Non-exhaust emissions are still significant.
Electric cars eliminate exhaust emissions of NOx and PM2.5, and reduce particulates from brake wear due to regenerative braking.
If they are heavier, they could increase tyre wear and road dust pollution.
Non-exhaust emissions need much more research, especially on solutions such as improved tyres, particulate filters, the role of more automated driving, and vehicle weight.
The best way to reduce local air pollution is to have fewer vehicles on the road.
We need to consider exhaust and non-exhaust emissions
When it comes to air pollution we need to consider a range of pollutants. There are particular gases, such as nitrogen oxides (NOx) which are particularly bad for human health. But there are also particulates – especially very small particles (which we call ‘PM2.5’) that can get lodged into our respiratory systems.
We also need to consider four sources of pollution:
Exhaust / tailpipe
Road wear and dust
The final three are collectively called ‘non-exhaust’ emissions. I’m going to go discuss each individually, but in the table, I’ve provided a quick summary of how EVs compare to gasoline cars.
Exhaust: Electric vehicles eliminate tailpipe emissions
The clear winner for EVs is the elimination of tailpipe (exhaust) emissions.
First, pollutants such as nitrogen oxides (called ‘NOx’) are generated from petrol and diesel cars. During combustion, nitrogen and oxygen in the air combine to form NO or NO2.1 NOx has been one of the biggest enemies when it comes to tackling air pollution – it has significant impacts on our respiratory health.
Second, these NOx compounds can react to form a ‘secondary’ pollutant – small particulates, termed ‘PM2.5’.
Third, these small particulates (PM2.5) also form directly from tailpipe emissions.
So, EVs reduce emissions of NOx, and PM2.5 emissions directly and indirectly.
Brake wear: Regenerative braking in EVs reduces brake wear
When a car slows down, the brake pads are pressed against the brake discs. This generates small particles from the wearing of these discs.
Brake wear in EVs is much lower than in gasoline cars. This is because most of the braking can be done through regenerative braking: this converts the energy from the moving vehicle into electricity, which is then used to recharge the battery. This reduces the wear of the brake discs.
In fact, some models use ‘brake drums’ which can capture the particulates within them so they’re not released to the environment.2 These are not as suitable in gasoline cars because the heat generated from braking needs to be released. However, the heat generated from regenerative braking in EVs is much less, so switching to ‘brake drums’ is an option.
Pollution from brake wear is much lower in EVs.
Tyre wear: Heavier vehicles tend to wear tyres more quickly
After clocking up miles on the road, you will eventually need to replace your tyres. This is because the friction on the road slowly wears them down, emitting particulates along the way.
This is a significant source of emissions. Yet the research on tyre wear is still lacking. One study hit the headlines when it claimed that tyres emit ‘more than 1,000 times as much pollution as exhausts’. There are a few reasons why we should be cautious about this result. The first comes from a small sense check on the numbers [see the footnote for details].3 The second is that most of the particles (by mass) that are emitted from tyres are large, and large particles are less problematic for air quality and human health. It’s the very small particles – less than 2.5 microns – that we’re worried about. A much smaller fraction of these particles will be in that size range.
So, I think the ‘1,000 times as much’ headline is too high. But, tyre wear is still significant and we need more research on it.
There are a range of factors that affect the rate of tyre wear.
A key one is weight: as cars get heavier, they tend to wear more quickly.
Other factors – which actually affect tyre wear more – are the types of tyres and driving style. Aggressive driving with high rates of acceleration, braking, and turning really ramps up tyre wear.
We might expect that EVs have higher tyre wear as they tend to be a few hundred kilograms heavier than their petrol equivalents (although I don’t think this will always be the case).
The truth is that we don’t have good studies that accurately compare the rates of tyre wear in EVs compared to gasoline cars. Real-life anecdotal evidence suggests that rates of tyre wear are pretty similar. The rear tyres tend to wear at the same rate, and the front tyres on EVs wear a bit faster due to increased torque; probably by around 10% to 15%.
Road dust: Bigger vehicles tend to create more road wear
You’re standing at the side of the road on a dry day. A big truck goes past and you get dust blown in your eyes.
Road wear and dust is something that most of us experience, but tend to forget when we think of ‘air pollution’. Most of these particles are too big to affect human health, but there will be some that are in the small range that we’re concerned about.
In general, the bigger vehicles resuspend more dust. However, this is probably more about aerodynamics (the size of the vehicle) than its weight.
But if EVs are bigger (again, an assumption we can challenge later) then road dust could be higher.
Electric vehicles eliminate tailpipe emissions and tend to have slightly lower particulate emissions
Okay, enough speculating. Let’s get to the comparisons. What happens when we consider all of these factors together?
First, NOx and other tailpipe emissions are eliminated in EVs. That is already a massive win. We’ll come to the impact of pollution from electricity generation later.
What about particulates? Here we’ll focus on the smallest ones – PM2.5 – but the results for a slightly higher cut-off – PM10 – are similar.
An OECD study looked at emissions of PM2.5 across different vehicle types.4 It assumed that EVs were around one-third heavier than their petrol and diesel equivalents. So, a small petrol car weighed around 1500 kilograms, and the EV model weighed 2000 kilograms. An SUV weighed 1800 kilograms, and the EV SUV weighed 2400 kilograms. That means they were mostly testing what happens when you increase the weight of the car.
The results for non-exhaust emissions are shown in the chart below. It found that there was little difference between petrol cars and EVs. EVs had less brake wear, but more tyre and road wear due to their increased weight. If they were the same weight, EVs would have lower emissions.
We can add exhaust emissions below. You might be surprised by how low these are, compared to non-exhaust emissions. This wasn’t always the case; continued tightening of air quality standards has led to a dramatic reduction in exhaust emissions.
With exhaust emissions included, electric cars emit less. Timmers and Achten (2015) give a good overview of petrol and diesel standards over time and find the same as the OECD: electric cars emit slightly less PM2.5, but not by much if they’re heavier.5 If the cars were the same weight, emissions from EVs would be even lower.
Another study found similar results.6
The chart below shows the relationship between PM2.5 pollution and car weight on different road types. Emissions from petrol cars are in green. Emissions from EVs with different levels of regenerative braking are in grey, red, and blue. As you can see, for a given weight, EVs emit less especially with regenerative braking.
Now, this study assessed the emissions of EVs compared to petrol cars assuming that they were heavier. Despite the heavier weight, it found that a switch to EVs would reduce PM2.5 emissions. This was true on urban roads, rural roads, and motorways. And it was true with a switch from small, medium and large petrol cars to their EV equivalents.
What made a difference was the amount of regenerative braking used. In fact, with no regenerative braking, PM2.5 increased by a few percentage points. But once included, emissions were around 10% lower with 50% regenerative braking, and around 25% lower with 100% braking.
What about pollution from electricity generation?
These studies focused on emissions generated by the car itself. Electricity plants further up the supply chain weren’t included. If your EVs are powered by coal, then that has consequences for air pollution too.
Here there are a few things to consider.
The first is location: shifting to EVs might still reduce human health impacts – even if the total emissions increase – because you’re shifting pollution from population-dense cities to areas with low population density. Many countries have reduced urban air pollution simply by moving power plants and industries out of population centres.
The second is that some countries already have very low-carbon grids. Countries such as Norway and Sweden (which have adopted EVs quickly) get nearly all of their electricity from clean sources. There, the emissions from power generation will be close to zero. For countries with fossil-heavy grids, this will be significantly different.
Third is how pollution levels will change over time as electricity grids decarbonise. Countries such as the US, and many across Europe, have set targets to fully decarbonise their electricity grids by 2035. At this point, electricity generation emissions will be close to zero.
A number of studies have analysed the pollution impacts when electricity generation is included. Most suggest that EVs still reduce total air pollution; the difference is by how much. Here’s a quick summary:
A study by Peters et al. (2020) found that a 25% electrification of cars in the US with the current electricity mix would result in air pollution reductions, albeit modest ones. A 75% adoption, especially when combined with a cleaner grid would reduce pollution significantly.7
A study by the University of Berkeley – ‘2035 Report’ – projects that an accelerated move to EVs would prevent around 150,000 premature deaths in the US due to reductions in air pollution through 2050. It would save a further 90,000 when combined with a 90% clean electricity grid.
Lin et al. (2020) modelled the impacts of a transition to EVs on air pollution when the electricity was generated from extra coal. It tested how pollution changed depending on the location of the plant. There were still significant improvements in air quality when electricity emissions were included. The size of reductions depended on the location of the plants.8
Soret et al. (2014) assessed the impacts of EV introduction in Barcelona and Madrid. They found that air quality improved, despite additional emissions from electricity generation.9
The ICCT estimates that NOx emissions would be reduced significantly with EV uptake in India, even if the electricity mix did not change; India gets around three-quarters of its electricity from coal.
A recent report by the World Bank estimates that particulate matter would be reduced significantly with a shift to electric vehicles in India, despite increased emissions from electricity generation.10
A report from the European Environment Agency (EEA) expects that NOx emissions will be reduced, even with the current electricity mixes across the region. However, there are likely no significant reductions in PM2.5. Moves to a cleaner mix would increase air quality further.
Electric cars improve but do not eliminate road pollution – but there are other ways to reduce this
Just as with carbon emissions, moving to EVs will improve air quality, but it is not an immediate perfect fix. Local emissions such as NOx are eliminated from tailpipes and PM2.5 emissions also tend to be lower.
Non-exhaust emissions from cars have mostly been overlooked in policy and research because they’ve been dwarfed by exhaust emissions. But, significant reductions in exhaust emissions in modern cars mean that they’re becoming more important. Now that most particulates come from non-exhaust sources, reducing pollution further (regardless of whether it’s EVs or petrol cars) means we need to find new solutions to those sources. This paper gives a good overview of the open research questions.11
Here, several things matter. As I covered in another post, EVs tend to be slightly heavier today, but it won’t always be this way. Improvements in battery technologies, and an emerging market for smaller, more affordable EVs could bring their weight down significantly. Meanwhile, ICE cars continue to move towards bigger models – SUV sales are on the rise – so increased weight will be a problem anyway.
Second, emissions from electricity generation will fall as countries decarbonise their grids.
But there are things we can do to reduce pollution further, regardless of whether they’re electric or gasoline gas. We could install filters on larger vehicles, such as trucks, to capture particulates from tyres and road dust. Some companies are already doing this.
We can design better tyres that wear less often. Reduce the dust from our roads. And a shift towards more automated driving could reduce aggressive stops and starts.
The final, and most obvious point is that the best way to reduce non-exhaust emissions is to have fewer cars overall: cities built around public transport, cycling and walking remain the ultimate winner.
The amount of NOx generation depends on the combustion temperature. A higher temperature means more NOx.
Driving actions that demand high engine power – such as rapid acceleration or driving uphill – increase the combustion temperature and generate more NOx.
NOx emissions can (and have been) reduced through technological improvements such as the use of catalytic converters and increasing vehicle standards.
Grigoratos, T., Mathissen, M., Vedula, R., Mamakos, A., Agudelo, C., Gramstat, S. and Giechaskiel, B., Interlaboratory Study on Brake Particle Emissions – Part I: Particulate Matter Mass Emissions, ATMOSPHERE, ISSN 2073-4433, 14 (3), 2023, p. 498, JRC132675.
This result is based on the figure that 9.3 grams of particulates are emitted per mile from the tyres. A typical tyre might weigh around 9 kilograms. At that rate of loss, the tyre would be completely gone within 4,000 miles. And since the thread of the tyre is only around one-third of the weight, it’d be gone within 1,400 miles. If someone drives around 20 miles a day, they’d be changing the tyres every two months.
OECD (2020), Non-exhaust Particulate Emissions from Road Transport: An Ignored Environmental Policy Challenge, OECD Publishing, Paris, https://doi.org/10.1787/4a4dc6ca-en.
Timmers, V. R., & Achten, P. A. (2016). Non-exhaust PM emissions from electric vehicles. Atmospheric environment, 134, 10-17.
Liu, Y., Chen, H., Gao, J., Li, Y., Dave, K., Chen, J., ... & Perricone, G. (2021). Comparative analysis of non-exhaust airborne particles from electric and internal combustion engine vehicles. Journal of Hazardous Materials, 420, 126626.
Peters, D. R., Schnell, J. L., Kinney, P. L., Naik, V., & Horton, D. E. (2020). Public health and climate benefits and trade‐offs of US vehicle electrification. GeoHealth, 4(10), e2020GH000275.
Lin, W. Y., Hsiao, M. C., Wu, P. C., Fu, J. S., Lai, L. W., & Lai, H. C. (2020). Analysis of air quality and health co-benefits regarding electric vehicle promotion coupled with power plant emissions. Journal of Cleaner Production, 247, 119152.
Soret, A., Guevara, M., & Baldasano, J. M. (2014). The potential impacts of electric vehicles on air quality in the urban areas of Barcelona and Madrid (Spain). Atmospheric environment, 99, 51-63.
As far as I can see, this study did not include emissions from non-exhaust sources.
But even if non-exhaust emissions increased slightly, this would not be enough to offset the gains in eliminating tailpipe emissions.
Fussell, J. C., Franklin, M., Green, D. C., Gustafsson, M., Harrison, R. M., Hicks, W., ... & Zhu, Y. (2022). A review of road traffic-derived non-exhaust particles: Emissions, physicochemical characteristics, health risks, and mitigation measures. Environmental Science & Technology, 56(11), 6813-6835.