Whoops

Emissions Analytics are an outfit that, as their name implies, analyses emissions. They were in the news six years ago when they showed that emissions from diesels were worse than we thought. They also measured real-world fuel economies and found that they were worse than advertised.

Searching Google News shows that the Guardian picked up the diesel emissions story. It has not yet picked up Emissions Analytics’ latest “worse than we thought” emissions story, or if it has, Google is not aware of that fact.

If that omission surprised a jaundiced climate cynic, his raised eyebrows probably settled back to their accustomed lodgement when they read the new headline from Emissions Analytics:

Gaining traction, losing tread

Pollution from tire wear now 1,850 times worse than exhaust emissions

Emissions Analytics, wisely diversifying into non-exhaust emissions from surface vehicles, found in 2020 that particulate emissions from tyre wear now dwarfs that from (new) engines.

On the one hand, we have the improved filtration unit on diesel cars:

Filters are so good that we have measured that in certain circumstances, when the ambient air is already polluted, a diesel car will tend to extract more particles from the air than it emits.

Not something that I would have predicted.

On a polluted day where ambient concentrations of particles are already high at 50,000 #/cm3, the vehicles remove on average 27,984 particles per second of operation.

[They still pollute on clean-air days.]

At the moment it sounds as if new diesels could be described as mobile air filtration units. As particulates concern me far more than CO2 emissions (which don’t concern me at all in fact), this sounds like a big tick for diesels.

On the other hand, tyre wear is surprisingly high:

Driving a 2011 VW Golf 320kms at high road speeds on the track resulted in a mass loss of 1,844g which equates 5.8g per km. This was 29 times worse than our hypothesis, and partly explained by our deliberate quest for a ‘worst case scenario’. It should be noted that the driving and vehicle payload would be aggressive but legal if conducted on the public highway.

The mass loss from tyres was >1000 times higher than permitted particulate emissions from exhausts:

Nevertheless, it is a very high figure: 5,760mg/km of completely unregulated tyre wear emission versus regulated exhaust emission limits of 4.5mg/km – a factor of over 1,000.

Yea, I hear you cry, but these are big lumps and are not remotely comparable to the smoke coming out of a diesel. You probably have in mind the tracksides after an F1 race. And yes, most of the mass lost falls straight to the ground. But:

…the tyre wear emissions also included a high number of particles down to 10nm, as a result of volatilisation of the tyre material due to heat in the tyres. Therefore, tyres shed material that both leads to microplastics in the watercourse, and ultrafines that compromise air quality.

That was 2020. In 2022, Emissions Analytics have revisited tyre wear.

They note that their previous work had made electric vehicle drivers a little twitchy:

Particularly vocal were the battery electric vehicle (BEV) community, sensitive to any suggestion that the added weight of these vehicles might lead to tire wear emissions that might confound the ‘zero emissions’ tag.  Such was the reaction, the story was translated into over 40 languages worldwide.

Now, in the first study they loaded up a golf and threw it around a race track to measure tyre mass loss – that’s because they were worried that if they drove it normally at low weight they wouldn’t be able to measure the mass loss. But in 2022, they report wear under “normal” conditions:

The headline conclusion we draw now is that, comparing real-world tailpipe particulate mass emissions to tire wear emissions, both in ‘normal’ driving, the latter is actually around 1,850 times greater than the former.  Yes, in normal driving the ratio is almost double the previous figure for aggressive driving.

This seems counterintuitive, but:

Tailpipe emissions are falling over time, as exhaust filters become more efficient and with the prospect of extending the measurement of particulates under the potential future Euro 7 regulation, while tire wear emissions are rising as vehicles become heavier and added power and torque is placed at the driver’s disposal.  On current trends, the ratio may well continue to increase.

Heavier… torque… power…

An image is forming in my mind…

Are they by any chance talking about cars that are carrying a little extra around the middle because they run on battery power?

Anyway, what was it I was saying the other day? A picture paints a thousand words? Here is their provided figure:

Figure by Emissions Analytics at above link

The bar on the left is mass loss from the 2020 Golf study. The next two bars are tyre wear from new or used tyres. The next is airborne (fine particle) emissions from normal driving on new tyres. Then we have the additional wear from +500 kg on the vehicle, then the legal limit for tailpipe particulates, then tailpipe particulates of new diesels. Note the log scale.

Tailpipe emissions are now 1/250th of the legal maximum. Airborne tyre wear on new tyres with normal driving already exceeds the legal tailpipe limit. So it’s not just lumpy bits.

…11% of the mass of tire emissions is smaller than 2.5 microns in diameter (defining the common metric for fine particle dust, PM2.5, which can be airborne). Therefore, the airborne tire emissions are more likely to be around 8 mg/km as shown in the table above – this is still more than 400 times higher than tailpipe emissions.

Emissions Analytics are now working on finding out what lovely toxins are present in these ultrafine particles.

I don’t think electric vehicle drivers are going to want to know. Will the Guardian?

Final point: these guys are engineers, so they probably know what they’re doing. Nevertheless, we don’t want to seize on data that supports our worldview just because it supports our worldview. Other groups need to replicate or refute this study before we start up the Muttley laugh.

But on this data, EVs could be the next CFT.

13 Comments

  1. Sorry Mark. There is a finite chance that I meant CFL. In any case I was referring to those little twisted lightbulbs that were being handed out in vast numbers a few years ago as better than incandescents, only to prove worse.

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  2. Well, that *was* an interesting post, Jit. Thanks for sharing the info.

    Perhaps Emissions Analytics could now be working on finding out what amount of particles there are from cars with ‘normal’ braking vs cars with an extra 500 kg mass and regenerative braking.

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  3. The RAC seems to have commissioned a report to cast doubt on EVs being worse than diesel or petrol cars when it comes to particulates from tyres and brakes:

    “Do electric vehicles produce more tyre and brake pollution than their petrol and diesel equivalents?”

    https://www.rac.co.uk/drive/electric-cars/running/do-electric-vehicles-produce-more-tyre-and-brake-pollution-than-petrol-and/

    “So, in conclusion, electric vehicles already vastly reduce particulate matter from brake wear, and claims of tyre wear contributing 1,000 times the particulate matter pollution of petrol and diesel exhausts are greatly overexaggerated. Real EV fleets are already seeing brake lifespans increased fourfold versus the diesel vehicles they have replaced, and tyre wear that is broadly on par with petrol and diesel cars (unless, as like with any vehicle, the drivers get a bit throttle happy!).

    One final thought on emissions to end with: the UK is set to close its last remaining coal-fired power plants, but even if EVs were 100% powered by coal, it is much easier to fit particulate filters to a small number of very large, static power plants located away from city centres, than it is to fit effective filters to millions of small, mobile petrol and diesel engines running in urban areas.

    The end result is that cities that have embraced EVs have already demonstrably benefitted from reduced pollution and improved air quality, and this trend shall only continue as more EVs switch to drum brakes, new tyres are developed that reduce nanoparticulate pollution even further, and the UK’s grid becomes ever increasingly powered by clean renewable energy.”

    It was written by Dr Euan McTurk, and I am in no position to contradict his findings. It does read to me, though, a little as though he doth protest too much, and a quick internet search reveals that he has skin in the game:

    “Dr Euan McTurk is an expert in electric vehicle charging technology. Based in Inverkeithing, he runs Plug Life Consulting.”

    https://www.thecourier.co.uk/fp/business-environment/transport/2970129/relief-for-ev-drivers-as-perth-electric-car-charging-hub-to-open-later-this-year/

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  4. Mark, I’m prepared to believe that Emissions Analytics’ claims are exaggerated. But McTurk’s commentary does appear to have a few holes in it. If EVs have comparable tyre wear to conventional vehicles, some magic has gone on with the extra 500 kg of mass. It is possible that having four-wheel drive reduces oversteer and consequently wear on front tyres as folk drive around roundabouts. But that should be balanced by reduced wear on free rolling wheels.

    If new materials are going to produce better tyres, then such tyres could also be used on the lighter vehicles.

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  5. Hi JIT – Interesting read.

    TV ads – https://dieselemissionclaims.co.uk/ seem to be the latest “ambulance chasers” on diesel cars/vans/etc

    from the site “What is the Diesel Emission SCANDAL?
    Vehicle software cheated air pollution tests by adjusting the engine to emit less and make it look like a low-emissions vehicle, when in fact they were emitting dangerous levels of pollutants.”

    “Vehicle software cheated air pollution tests” !!!

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  6. Here’s the thing:

    Tyre emissions are produced by wear on the tyre. Therefore to minimise the emissions wear has to be reduced. Hence the life of the tyre will increase, which suggests that the aim, therefore, would be a tyre which had, if not an infinite life, then one which matched the life expected of the vehicle.

    I can’t see the tyre manufacturers being too happy with this prospect. I suspect it ain’t gonna happen.

    Also, a tyre that minimises wear is likely to produce less grip, which would raise other safety concerns.

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  7. Bill, I think you are right in that there will be a tradeoff between durability and grip.

    On the other hand, if you want to change the velocity of a car then the force acting where the rubber meets the road is proportional to the mass of said car, so presumably lighter cars have lower tyre wear, which is what Emissions Analytics is getting at. You could also reduce the scale of velocity changes. As an example, in our dystopian future where every car is tethered to the one in front by some automagical device, then those compression waves we see on motorways could be eliminated. Even replacing roundabouts with crossroads could help by reducing cornering speeds. And of course reducing speed limits would naturally decrease tyre wear. I’m not advocating any of these things because I’m still at the stage where I can’t quite believe the data as have been presented. But I would like it if drivers in our fine city actually stuck to the presently prescribed limit, just to make it easier to cross the road.

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  8. “Electric cars should face ‘tyre tax’, says air quality adviser
    Particulates generated by tyre wear are more dangerous to public health than diesel exhaust fumes, a Government expert claims”

    https://www.telegraph.co.uk/business/2022/05/30/electric-cars-should-face-tyre-tax-says-air-quality-adviser/

    “A ‘tyre tax’ will need to be imposed on electric cars to combat poor air quality in cities, the Government’s top clear air adviser has claimed.

    The chairman of the Government’s independent science advisory group on air pollution said charges for low-emission zones are likely to be replaced with alternative levies as drivers switch to electric vehicles.

    Particles from tyre wear are more dangerous to public health than diesel exhaust fumes, Professor Alastair Lewis said.

    Known as “particulate matter (PM) 2.5”, the amount of air pollution is growing because motorists are driving ever larger vehicles with more substantial tyres.

    Professor Lewis said: “If you compare a modern Mini now with an old Mini, they’re almost unrecognisable in their size.

    “[And] larger, heavier vehicles will generate more particles.”…

    …Professor Lewis, also chairman of the Department for Transport Science Advisory Council, said: “When everybody owns a low emissions vehicle, low emission zones become a toothless control lever to try to manage air pollution.

    “A world where we [have] jam-packed roads full of electric cars [also] isn’t a particularly attractive one… Even if they are electric, [they] will generate lots of particles.”

    “At some point in the future when most of those cars have disappeared, a different form of air pollution control” is likely to be needed, he added.

    “We do have to project forward about how we’re going to manage vehicles in large cities like London in the future when we have a largely electrified fleet of vehicles.”

    Luke Bosdet, an AA spokesman, said he was opposed to the idea of any tax on an electric vehicle which would act as a deterrent to them replacing traditional petrol or diesel vehicles….”

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  9. Thanks Mark. I had seen that story but hadn’t got around to posting it here. Seems I was wrong before – someone with the ear of power, and at least a part of the media, have noticed Emissions Analytics’ stuff after all.

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  10. “Car tyres produce vastly more particle pollution than exhausts, tests show
    Toxic particles from tyre wear almost 2,000 times worse than from exhausts as weight of cars increases”

    https://www.theguardian.com/environment/2022/jun/03/car-tyres-produce-more-particle-pollution-than-exhausts-tests-show

    “Almost 2,000 times more particle pollution is produced by tyre wear than is pumped out of the exhausts of modern cars, tests have shown.

    The tyre particles pollute air, water and soil and contain a wide range of toxic organic compounds, including known carcinogens, the analysts say, suggesting tyre pollution could rapidly become a major issue for regulators.

    Air pollution causes millions of early deaths a year globally. The requirement for better filters has meant particle emissions from tailpipes in developed countries are now much lower in new cars, with those in Europe far below the legal limit. However, the increasing weight of cars means more particles are being thrown off by tyres as they wear on the road.”

    Being the Guardian it seeks to downplay the possibility that EVs might be worse than ICE vehicles:

    “…The average weight of all cars has been increasing. But there has been particular debate over whether battery electric vehicles (BEVs), which are heavier than conventional cars and can have greater wheel torque, may lead to more tyre particles being produced. Molden said it would depend on driving style, with gentle EV drivers producing fewer particles than fossil-fuelled cars driven badly, though on average he expected slightly higher tyre particles from BEVs.

    Dr James Tate, at the University of Leeds’ Institute for Transport Studies in the UK, said the tyre test results were credible. “But it is very important to note that BEVs are becoming lighter very fast,” he said. “By 2024-25 we expect BEVs and [fossil-fuelled] city cars will have comparable weights. Only high-end, large BEVs with high capacity batteries will weigh more.”…”.

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  11. Mark, it is interesting that the Guardian has noticed this story. I must say I find Dr. Tate’s optimism very hard to believe. The mass differential between the Volvo XC40 ICE/EV as mentioned in “Slips the Green Halo” was given as: ICE 1690 kg and EV 2170 kg. That’s a difference of 480 kg, close to the Emissions Analytics’ used value of 500 kg.

    Of that 480 kg difference, the battery accounts for 350 kg. I would expect that, exempting the battery, the EV would be lighter, but seemingly not.

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