Do Electric Cars Generate as Much Particulate Pollution as Gas and Diesel Powered Cars?

UPDATE: We noted some skepticism about this post when we originally posted it, but now it has been pretty much debunked. please see comments. I am not taking it off the site because a) there is good discussion in comments and b) I stand by the position that "cars are cars" and heavier cars are worse than light cars, whether gas or electric.

George Monbiot tweets about an interesting and controversial study that came out a few months ago that concluded that electric cars put out particulate emissions that are as high as those from diesel and internal combustion engine powered cars(ICEV). PM2.5 particles are the deadly ones that get deep into lungs and are a matter of real concern, and usually identified with diesel.

The response from the Twitterverse is immediate and harsh; that it must have been funded by oil companies, that it’s bad science. But there is a certain logic in argument. The authors of the study claim that much of the particulate pollution is caused by brakes, tire wear and resuspension, or stirring up debris that is on the ground already. The main problem is that batteries make electric cars heavier and therefore create more wear of tires and roads. Green Car Congress reprints part of the paywalled study:

... 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 tyres and the road, as well as a function of the normal force of the road. 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.

And again, the reaction is instant:

I believe this is one of the most irresponsible and MORONIC studies I've seen in years.

© Timmers, Ashten/ click here for larger version

Many of the complainers note that there is not going to be any pollution from brake wear because most electric cars have regenerative braking. In fact, when you look at the data in the study, they assume that; they list the contribution from brake wear as zero. It is almost entirely from road wear, tire wear and the controversial resuspension, (which commenters question as being irrelevant) and all increase in proportion to weight. Then the complainers say that electric cars are not that heavy, but look at the Tesla Model X SUV. Most electric cars are heavier than their non-electric comparables.

© Copenhagenize

In the end, I believe that this study provides a valuable service. It reminds us once again that electric cars are still cars, and they still pollute, more or less depending on what their power sources are. I wrote earlier in an article where I accepted that the air would be so much cleaner in an electrified world (and was strongly criticized for ignoring the pollution that comes from generating the power that charges electric cars):

If you just changed every car from gas to electric it wouldn’t change sprawl, or congestion, or commute times or parking issues, or clashes and crashes with pedestrians and cyclists, all those other issues that we rant about.

And as for electric SUVs, they do not belong in cities anymore than regular SUVs do, especially if it is true at all that pollution is proportional to weight.

Electric car fans are passionate, but instead of complaining so much about this study, they should admit that weight is an issue for all cars, electric and gas, and as the abstract concludes, “Future policy should consequently focus on setting standards for non-exhaust emissions and encouraging weight reduction of all vehicles to significantly reduce PM emissions from traffic.”

Perhaps future policy should also focus on reducing the need for cars altogether, since electric vehicles are clearly not the panacea for every problem.