Do electric cars create more particulate pollution than petrol cars?

Question

I have seen some reports saying that electric cars, because they are heavier and put more strain on the tyres, will create more particulate pollution than a petrol car.

Is this true? and if so what are the differences?

Answer 1

Battery Weight

Batteries are heavy - a Tesla 85kWh battery weighs 540kg. - VW Golf 55.7kWh battery weight 330kg you are looking at around 6kg per kWh.

The main part of this argument is based on how much heavier an EV is and how much more shedding of the components and road will occur due to that additional weight.

How much heavier are electric cars?

I compared vehicles that had an electric version and a non electric version of the same model. This is so that we can compare the differences in weight in cars that are the same in terms of size and componentry, except for the difference of being electric and being non electric. We don't want to compare a Tesla ModelX to a Smart ForTwo petrol car!

Medium cars

The 235 mile Kia e-Niro 64 kWh is a good fit for comparison - it weighs 1,812kg and the petrol versions are somewhere between 1,490kg & 1,594kg depending on model. So here the electric version would be 12% - 18% heavier.

The additional weight is just the extra weight of the battery; electric components weigh less and they are simpler (no clutch, combustion engines are heavy and related to engine size).

For small cars

The Smart EQ 79 mile range ForTwo coupe with 17.2kWh battery weighs 1,095kg. The older ForTwo petrol version weighed 880kg. So the electric version would be about 20% heavier. If it was possible to have a battery with a range of 235m you would need another battery of

((17.2kWh / 79m) x 235m) - 17.2kWh = 54kWh battery

which would weigh another 203kg. That would mean the small car would be 33% heavier at the same range as the Kia.

Weight in electric vehicles also compares strongly with range, the longer the range the bigger the battery the extra size. These are difficult comparisons but it seems like you could say electric vehicles are somewhere between 10 and 30% heavier for electric cars. It is also obvious that some vehicles are unnecessarily heavy.

Other benefits of Electric Cars regarding particulate emissions

Electric cars will have much less brake pad wear because they will have regenertive brakes. Brake pad wear can normally account for 30% (ish) of the particulate emissions from cars (although drum brakes would also reduce the amount of brake pad particulates and wouldn't need to be electric).

Electric vehicles have smoother acceleration so may not wear the tyres so much but...due to the extra torquen in an electric motor, maybe there is no difference (please correct me here!). Also electric vehicles won't have a clutch which could add a little to wear.

Conclusion

If the amount of tyre and road particulate matter generated is proportional to the extra weight then I think generally there isn't going to be much difference in particulate emissions, especially if you factor in the regenerative breaking savings. However, battery weight needs to be factored in and the larger the battery the more particulates generated from tyre and road wear.

Other improvements

There are few regulations on materials and particulate emissions for brake pads, tyres, clutches and how roads are made and maintained. Also there are few reliable studies and many variables (a wet country wouldn't have so much redistribution of particulates as a dry country). Also, how do you compare? Do you compare a car with or without drum brakes.

I think the real problem is unnecessarily heavy cars, poor traffic management with many stop starts in a journey, poor regulations on compositions of tyres and other componentry and better driving behaviour that reduces unnecessary acceleration and braking. Electric vehicles have obvious other benefits like zero particulates from the exhaust, zero NO2 from the exhaust, much less CO2 emissions (50% including manufacture??? if using mostly renewables), they have longer lives too.

Longer ranges from EVs could also be gained from battery swap stations similar to those in China so that large heavy batteries are used less often or are only swapped in on longer journeys.

https://publications.jrc.ec.europa.eu/repository/bitstream/JRC89231/jrc89231-online%20final%20version%202.pdf

https://uk-air.defra.gov.uk/assets/documents/reports/cat09/1907101151_20190709_Non_Exhaust_Emissions_typeset_Final.pdf

Answer 2

No. Electric cars emit less particulates.

Main sources of particulate emissions from transport are:

1. brake wear
2. tyre wear
3. road wear and resuspension of road dust/soil
4. exhaust

Exhaust particulate emissions are zero for electric cars. Brake wear is significantly (66% estimated) less for electric cars due to regenerative braking. Tyre wear is related approximately linearly to vehicle weight, so will be around 10-30% more for electric cars. Road wear and resuspension are roughly equivalent between electric and petrol or diesel cars.

The net effect is that electric cars emit less particulates. Estimates vary between: 1-3% less (Timmers/Achten Atmospheric Environment 134 (2016) 10-17) and 50% less (Hooftman et al, Energies 2016, 9, 84).

Note that for the newest internal combustion engines particulate emissions are already dominated by non-exhaust sources. As ICEs become more efficient and cleaner (a long-term trend, driven partly by regulation) there may come a crossing point where ICEs produce less total particulates.

You should also note that for many other pollutants (VOCs, NOx, CO2, photochemical oxidants, etc) electric cars provide significant benefits over ICEs - Timmers & Achten1 estimate overall 2x better than petrol and 8x better than diesel for human health (based on disability-adjusted life years, and including the effects of electricity generation).

Answer 3

Wheels and tires can be easily sized to vehicle weight. Also, short-sidewall tires are tires that wiggle less and are now a standard technology. And the short-sidewall tires tend to be wider tires.

But battery-powered electric-vehicles might have low-rolling-resistance-rubber-compound tires. And the low-rolling-resistance tires might be narrower tires. However, there are roll-center-height suspension designs for narrow tires such that traction capability is maintained at some level. Now if these narrower tires control tire wiggle, it's probably because of stiffer and harder rubber compounds or because of thicker sidewall construction.

Overall, I wouldn't expect battery-powered electric-vehicles to have drastically over-stressed tires. But look for an extended-range model with the same tire size as a standard-range model and the tires on the extended-range model are likely more stressed than the tires on the standard-range model.

Considering the weight of battery-powered electric-vehicles, the BMW i3 and the original Tesla roadster both weigh less than 3000 pounds and that makes a benchmark.

What is wrong with electric-vehicles at 4000 to 5500 pounds or more weight ? I would look for flaws in the MPGe system for an answer. https://en.wikipedia.org/wiki/Miles_per_gallon_gasoline_equivalent

I suppose that the heavier longer-range battery-powered electric-vehicles make-up for heavy weight with larger amounts of motor torque. Just don't have one crash into your vehicle.