Motor Mouth: The next automotive emissions frontier—is tires

Article content

As if we didn’t have enough to worry about with global warming — the World Meteorological Society just announced “we are more likely than not” to breach the 2015 Paris Agreement 1.5-degree-C warming threshold in the next five years — now we have to worry about tires. Or, more accurately, the tire-wear particles (TWP) created when they grind, at high speed, against pavement. And, circling back to that climate-change scare, this tires-as-killer-pollutants scenario is made all the disturbing because EVs — and the incredibly heavy batteries that power them — produce a lot more TWP than conventional cars.

Article content

About 50 per cent more, in fact, says a recent report by Reuters, citing Michelin and Goodyear. “The unintended consequence of electric cars is we’ll have more tire pollution unless we have better tires,” said Gunnlaugur “G” Erlendsson, CEO of U.K.-based start-up Enso, which is developing more durable tires specifically for electric vehicles.

The numbers may be even worse than that here in North America, which is trying to solve its climate crisis by electrifying its enormous fleet of pickups and SUVs first. Already portly, the electrified versions of these rigs are positively humungous.

GMC’s Hummer EV, for instance, weighs 4,103 kilograms (9,046 pounds) and is powered by a battery that is heavier than a Honda Civic. Yes, an entire Honda Civic, tires and all. Not to be outdone, Ram is promising to offer its upcoming 1500 REV with a 229-kilowatt-hour option, with a battery that will almost certainly push past 3,000 pounds all by itself. Considering the weight disadvantages that even conventionally-powered SUVs suffer compared with their sedan equivalents, our conversion to battery power may cause more of these TWP problems than anywhere else on the planet.

Article content

The culprit in these tire emissions — at least the culprit we currently know of — is something called N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylenediamine, otherwise known as 6PPD. According to UStires.org, 6PPD “is an antioxidant and antiozonant that helps prevent the degradation and cracking of rubber compounds caused by exposure to oxygen, ozone, and temperature fluctuation.” Pictures supplied by the U.S. Tire Manufacturers Association (USTMA) show thoroughly cracked and degraded rubber identical to that in tire formulations, save for the lack of 6PPD. In other words, without the offending chemical, tire life — already a complaint with consumers as cars get increasingly heavier — would be even shorter.

Article content

However, as the USTMA points out, it’s not 6PPD itself which causes the problem, but rather something called 6PPD-quinone — rather a by-product that is transformed “once 6PPD reacts with oxygen and/or ozone.” As to the dangers of 6PPD-quinone, research is still in early days. Reuters reports that, while the chemical has been found in the urine of Chinese nationals with indeterminant effects, it “has been blamed for mass deaths of coho salmon off the U.S. West Coast.”

But just to show you how truly difficult emissions and health science really is, the researchers who discovered this acute toxicity amongst Oncorhynchus kisutch report that, while their sample group of cohos all perished when exposed to but moderate amounts of 6PPD-Quinone in their water, none of their closely-related cousins, chum salmon (Oncorhynchus keta), died no matter how high the levels were. In other words, either the chum are the Keith Richards of salmon, or else the question of what is toxic to whom (or what) is a lot more complicated than the blanket statements Twitter uses in trying to compress complicated emissions issues into 128 characters.

Article content

Making this issue a global problem is the fact Reuters says the two billion car tires produced every year create three million metric tonnes of these TWP particles annually. And just to show you how fragile nature really is, in the American Chemical Society study of the salmon — Treading Water: Tire Wear Particle Leachate Recreates an Urban Runoff Mortality Syndrome in Coho but Not Chum Salmon — the researchers found that fish mortality was “acute” immediately following rain events, and that mortalities were “correlated” with roadway density. This, despite the fact TWP leachates made up just 15 per cent of all the chemical “detections” in local roadway runoff. And, just so we don’t think it’s only American salmon being affected by leaching tire particles, a more recent Fisheries and Oceans Canada-backed study concluded that rainbow and brook trout fall into the coho arena of sensitivity, while Arctic char and white sturgeon react more like the chums.

Article content

According to CNN, fully 90 per cent of all particulate emissions from passenger vehicles come from tire and brakes, as well as road surface wear. Besides getting in our waterways, these produce PM2.5 pollution — sub-2.5-micrometer particulates — that are genuinely dangerous to human respiratory systems. According to the American Environmental Protection Agency, these ultra-small particles “pose the greatest problems, because they can get deep into your lungs, and some may even get into your bloodstream,” causing everything from asthma to heart attacks. And, because they can be carried over long distances by wind, PM2.5 particles can do everything from damage crops; to make lakes and streams acidic. And, of course, kill fish.

Article content

A London, England-based start-up, The Tyre Collective, has come up with at least a partial solution. Copper plates, hooked up to the car’s electric system, can create a magnetic field that attract the electrostatically charged TWP particles. In lab tests, the company’s prototype captured about 60 per cent of the airborne particles. The Collective hopes to launch a commercially-acceptable version of its particle accumulator in 2024, and it will be aimed first at fleets and commercial vans that can best integrate the plate cleaning — basically disconnect it from the battery, remove it from the car, and wash the particulates into a safe container — into their already scheduled maintenance.

As the recognition of the dangers of these PM2.5 particulates becomes more understood — and heavy EVs create more of them — controlling tire wear is going to become a more distinguished problem. Indeed, according to Reuters, California’s Department of Toxic Substances Control will become the first jurisdiction to require tire-makers find a safer alternative to 6PPD, and, within the next year, it is expected that the E.U. will agree on rules to curb both brake and tire emissions for its upcoming Euro 7 regulations. Further regulation can’t come quick enough, I suspect, for the coho and the fishing industry — both commercial and sports — that depend on the salmon for its livelihood.