A controversial study from a few months back suggests that EVs may emit as many particulates as gas or diesel vehicles.

The study suggests that EVs may do so not through engine emissions, but from the wear and tear of tires, or from the stirring up of road debris as the cars are driven. The study says that the batteries causes roads and tires to wear out faster. Initially there was concern also brake dust could add to the particulate count, but later researchers decided regen braking effectively reduces this concern.

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The study is behind a paywall, but an excerpt says: “It can be hypothesized that each of the sources of non-exhaust PM emissions should be influenced by vehicle weight. We know that road abrasion and tire wear are caused by the friction between the tire thread and road surface. Friction is a function of the friction coefficient between the tires and the road, as well as a function of the normal force of the road,” the study said. “This force is directly proportional to the weight of the car. This means that increasing vehicle weight would increase the frictional force and therefore the rate of wear on both the tire and road surface. Brake wear is caused by the friction between the brake pads and the wheels. The energy needed to reduce the momentum of a vehicle is proportional to the vehicle’s speed and mass. Therefore, as the mass of the vehicle increases, more frictional energy is needed to slow it down, leading to greater brake wear.”

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As might be predicted, the study has been harshly criticized online, with some in the Twitter universe saying that the study must be funded by oil companies or based on poor science. However, there is some truth to the idea that EVs may pollute in ways outside of exhaust emissions.

Whether the study’s conclusions are sound or not, it’s a reminder that even EVs do pollute at least on some level, and that reducing vehicle weight is a worthy goal, no matter what powertrain is used.