17

According to this Flanders Today (a local Belgian newspaper) article

a new small car on petrol in the city creates less fine dust than an electric car of average size.

The researcher, Bruno Van Zeebroeck, claims that this is because

Fine dust is created not just by a car’s motor but also by the wearing out of tyres and braking. Those so-called non-exhaust emissions are higher in electric cars because most of them are heavier than other kinds of cars. These non-exhaust emissions are a particular problem in the city, where drivers brake often.

[...] Van Zeebroeck pointed out that the test didn’t examine the smallest particles of fine dust, which are the most harmful to human health. These particles are mostly emitted by diesel-fuelled cars.

However, I can’t find any research that backs up this claim. Is there any truth in this?

Note: to be clear I'm not interested in possible dust particle emissions from electricity generation, but only emissions that stem from using the car so from tyre wear and braking of electric cars.

  • 2
    I would challenge this study based on comparing a new small (petrol) car vs. and average sized (electric) car – Phil N DeBlanc Feb 6 at 8:49
  • @PhilNDeBlanc: Well, that's the trick, isn't it? With much of the PM coming from tires and brakes, "making" the E car in the comparison even heavier allows the claim to be made in the first place. Besides, who is buying a small petrol car these days? SUVs are the craze... – DevSolar Feb 6 at 12:09
  • @DevSolar That study is from Belgium, where I currently live, and there are a lot of small petrol cars here. Giant SUVs? Not so much. – Phil N DeBlanc Feb 7 at 6:20
15

They certainly do not create more particulate emissions, but they might not create that much less than a gasoline powered car, depending on the model of car considered.

First, what was previously thought? According to point IV.a.55 of this report the council of Europe's standing committee on Science and Technology, electric vehicles produce no fine particulate emissions. The report is dated 1998 however, so things may have changed since.

The new study (perhaps 'review' or 'article' would be better? It's a think tank's internal publication, not peer reviewed) can be read in full here, but you need to look at the Dutch version for the graphs.

The very first section already answers our question. The author never claims that electric cars produce more particulate emissions than ordinary cars. The title of the section says it all: "Electric cars produce almost as much particulate matter (PM) [as] modern petrol or diesel cars".

The first graph in this section solidifies this. The electric cars considered all have lower total PM emissions than any of the similarly sized cars that are not EVs, though only modestly lower for the most part. A small gasoline car produces slightly less emissions than a medium sized EV however.

Figures 3 and 4 suggest that the reason the advantage is so small now is because tighter emissions standards have dramatically reduced PM from cars over the last 25 years. So when the council of Europe report was written, it probably was fair to say that electric vehicles had no PM emissions at all (as compared to existing gasoline powered cars), but this is apparently no longer true.

The last part of the section concerned with emissions seems very badly done to me, and at best is educated speculation. The author tries to mathematically compute an estimate for the increase in PM emissions from the extra weight of an electric car, but uses an unsourced formula with very nice round numbers, that I believe is likely to have been made up on the spot (33.33% factors for everything?). Even this slipshod analysis finds that the electric version of a normal family car is no worse than the gasoline version for PM emissions, and smaller EVs are much better.

On the whole, I think the news story ought to have been: "Emissions Standards so Good that Gasoline Cars Now Competitive with EVs!" which is still exciting, but doesn't mislead the reader into thinking this was always the case, or that it's an argument against EVs in and of itself (remember, EVs are unchanged at the level of PMs that Council of Europe considered to be zero. It's that gasoline powered cars have dropped by > 75% for gasoline, and even more for diesel since the report was written).

(Edit: Some of the original links have rotted. The Dutch report's title was belang niet uitlaat fijn stof emissies, which translates to The Importance of Fine Dust Emissions. The author is Bruno Van Zeebroeck. There is currently a version up here. I cannot find the Council of Europe's Report now, because it was indexed by a doi that not longer points at anything.).

  • 6
    Do electric cars use regenerative braking instead of friction-operated brake pads? – ChrisW Dec 30 '14 at 18:59
  • 2
    This is considered by the article, near the end of the section concerned with emissions. They conclude that the use of regenerative breaks offsets some of the brake pad dust emissions, but only a very small amount (16% as I recall...). However, I'm also not confident the methodology in that section is at all good. – John Doucette Dec 30 '14 at 19:25
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    This report umweltbundesamt.de/sites/default/files/medien/publikation/long/… (German Ministry of Environment, 2007) may give some useful estimates. According to their projection, the abrasion (both tires and brakes) : exhaust PM2.5 was to be about 1:1 in 2010 and 2:1 by now, and for cars (as opposed to small and large trucks) by now 4x as much abrasive PM2.5 than exhaust PM2.5. Other comparisons: PM2.5 by car exhaust is a bit more than PM2.5 by BBQs, 30% of PM2.5 by cigarette smoke or 62% of PM2.5 by fireworks (happy new year!). – cbeleites supports Monica Jan 14 '15 at 16:05
  • 1
    A related question just came up on Sustainability.SE, and I came here through some related questions. The two links in this answer are now broken. Do you remember the study title, to see if it can be found, or if subsequent research that cited it can be identified? – LShaver Feb 6 at 2:07
  • 2
    I found the original PDF; tmleuven.be/uploads/navigationtree/files/… – THelper Feb 6 at 7:50
0

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 flanderstoday.eu article above says 'Those so-called non-exhaust emissions are higher in electric cars because most of them are heavier than other kinds of cars' so, I think a large part of this claim 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 so it is first important to determine how much heavier an electric car is compared to a petrol car.

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 the car wouldn't need to be electric).

Electric vehicles have smoother acceleration so may not wear the tyres so much but...due to the extra torque 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

  • Welcome to Skeptics!This is an answer based purely on a theoretical model. We expect answers to be based on empirical evidence rather than speculative predictions. – Oddthinking Feb 6 at 22:43
  • @Oddthinking if you read the whole post on sustainability stack exchange it will make more sense, that is a quote. I have decided to copy and paste to avoid misunderstandings. There are references, calculations and weights taken from reliable sources that result in the conclusion I posted initially. – atreeon Feb 7 at 8:46
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    In the section "Other benefits of Electric Cars regarding particulate emissions" you make some key claims, but you don't back them up with references. You speculate. In fact your second references gives a somewhat different answer "The net balance between reductions in brake wear emissions and potential increases in tyre and road wear emissions and resuspension for vehicles with regenerative braking remains unquantified, and will depend upon road type and driving mode, as both influence the balance between the different sources of emissions." – Oddthinking Feb 7 at 13:24
  • "there are few reliable studies" Please provide some evidence of that. (It is a tricky one - normally we accept experts in the field explaining there are few studies. An appeal to authority, but a necessary one.) – Oddthinking Feb 7 at 13:26
  • "I think the real problem is..." the rest of this is a personal opinion, and not supported by references. – Oddthinking Feb 7 at 13:26
-5

The source of electricity may be a bigger issue than tyres and brakes.

The Economist had a recent article "Cleaner than what? Why an electric car may be much dirtier than a petrol one". It concluded

Overall, the research shows that electric cars are cleaner than those that rely on internal-combustion engines only if the power used to charge them is also clean. That is hardly a surprise, but the magnitude of the difference is. How green electric cars really are, then, will depend mainly on where they are driven. In France, which obtains more than half its power from nuclear stations, they look like a good bet. In China—which is keen on electric cars, but produces some 80% of its electricity from coal—rather less so.

It was pointing at a recent article "Life cycle air quality impacts of conventional and alternative light-duty transportation in the United States" by Christopher W. Tessuma, Jason D. Hill, and Julian D. Marshall in PNAS vol. 111 no. 52, 18490–18495, doi: 10.1073/pnas.1406853111, which included the following chart

enter image description here

Fig. 2. Air quality health impacts in the United States for each scenario: attributable increases in annual mortality (upper scale) and the resulting monetized health impacts (lower scale).

  • 2
    All that this shows is that using power generated from coal produces lots of PM output. The cars themselves do not produce more PMs than gasoline powered ones. Further, the Council of Europe's report in my answer notes that the reason PM emissions from EVs should be discounted is that the emissions do not need to be concentrated in densely populated areas, unlike the emissions from gasoline powered cars. – John Doucette Dec 30 '14 at 20:34
  • @John Doucette: I'm not sure people in China would necessarily agree that dispersion works. – Henry Dec 30 '14 at 21:28
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    The OP's claim is clearly not about emissions caused by the entire life cycle, so while interesting, this doesn't answer the question. – Is Begot Dec 31 '14 at 0:45
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    I think you mean to respond to @Geobits in your second comment? I'm not sure what your point is. Just because China hasn't made use of low-emissions fuels for their electricity generation, and hasn't or can't place their plants far from inhabited areas, doesn't mean that you couldn't do so elsewhere. In Germany or France for instance, PM emissions for EVs would be far lower because a much larger share of their electricity comes from cleaner sources. If the emissions depend on where you are, then clearly it's not a problem with the car -- it's a problem with your fuel. – John Doucette Dec 31 '14 at 1:52
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    @Henry There's a question more specifically asking about life cycle impact here. Nothing in the OP asks about anything other than point-of-use emissions (engine, tires, brakes, etc). – Is Begot Dec 31 '14 at 13:27

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