Nothing is easy. That’s the big takeaway here. Almost every system we encounter is full of unseen complexity. A great example of this is found in a new study that suggests that electric and hybrid vehicles may actually produce as many atmospheric toxins as combustion cars. How can this be, if they produce no exhaust? The answer is that they produce more non-exhaust emissions.

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A study by Victor Timmers and A.J. Achten at the University of Edinburgh has found that, when you factor in everything, electric vehicles produce as many particulate matter (PM) emissions as conventional ICE vehicles.

This isn’t even factoring in the pollutants created generating the electricity itself, from coal or other sources; these are pollutants released from actually driving the individual car. The types of pollutants we’re talking about are PM emissions. These types of emissions are not really the result of the exhaust of an internal-combustion engine: 90 percent of PM emissions are from non-exhaust sources.

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This is because the primary types of PM emissions—tire wear dust, brake pad dust, tiny road particles, and road dust re-suspension—are all factors that increase with the weight of a vehicle, and electric vehicles and hybrids, thanks to their dense battery packs, tend to weigh on average 24 percent more than fuel-burning cars.

Chart from Green Car Congress, based on data from Timmers and Achten study

Their findings suggest that in modern engines, the actual exhaust is only about one-third of the total vehicle emissions, and that those emissions are actually less harmful than the particulate emissions. In their report, Achten writes:

We found that non-exhaust emissions, from brakes, tyres and the road, are far larger than exhaust emissions in all modern cars. These are more toxic than emissions from modern engines so they are likely to be key factors in the extra heart attacks, strokes and asthma attacks seen when air pollution levels surge.

Of course, the exhaust emissions affect CO2 levels that the particulate emissions don’t, but as far as immediate health goes, the PM emissions do pose a greater threat.

So, Lotus had it right all along: weight is the enemy. Here, though, it’s not hindering performance, it’s increasing the emissions of cars that don’t technically emit anything.

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Now, the results may be a little misleading in some ways. What’s really being said here is that heavier vehicles will produce more particulates of everything: road dust, tire bits, brake pad powder, and so on.

It’s only an issue with electric cars because batteries are heavy; an electric car as light as an average gasoline car would get better results. Also, technically, even a horse cart would produce these particulate emissions, especially road dust re-suspension, which is one of the major sources of PM emissions.

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Hell, anything on the road would produce road dust. A hippo. A herd of rats. A giant, rolling boulder.

Also, electric vehicles’ regenerative braking might mitigate the brake dust production, though that may be offset by the greater weight when the brakes actually do get employed. Electric vehicles also tend to use harder tire compounds for less rolling resistance, and those compounds tend to – at least in my personal experience and not in a controlled study – break down into dryer, more dust-like particles than conventional tires.

That said, PM emissions are no joke, and can cause significant health issues. The solution here could take many forms: reduction of automobile weight, perhaps new road, tire and brake compounds?

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There’s still many factors here, and a lot of variables, but I think there’s just enough here that EV and hybrid drivers can safely take this as a reason to be just a hair less smug about things. At least until we figure out lighter batteries.