No Smoke Without Tyres


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.

via Climate Scepticism

May 21, 2022 at 10:55AM

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