It's true that brake dust is the primary PM2.5 emission from vehicles in an urban environment. However the PM2.5 component from tail pipes are still very significant, higher than the contribution from tires.

The order is:

1. brake dust 2. road dust 3. engine emissions 4. tire dust

https://www.sciencedirect.com/science/article/abs/pii/S00456...

https://electrek.co/2025/05/27/another-way-electric-cars-cle...

> though diesel engines spit out a bunch of bad stuff.

Exactly. The noxious tailpipe emissions in a city are usually from diesel trucks, small vehicles like motorcycles (small or absent catalytic converters), modified vehicles (catalytic converter removed or diesel reprogrammed to smoke), but not modern gasoline ICE vehicles.

The love for diesel engines in many European countries was always confusing to me.

PM2.5 is also a broad category of particulates that come from many sources. The PM2.5 levels in the air depend on many sources, with wind being a major factor in changing PM2.5 levels. It’s hard to draw conclusions when a number depends on the weather and a lot of other inputs.

"relatively clean" means 85% of PM2.5 is from non-exhaust sources, and 15% is from exhaust after catalytic conversion. In New York EV and ICE are pretty much on par when it comes to this category of pollution, as the additional weight increases non exhaust sources. Source: https://www.sciencedirect.com/science/article/abs/pii/S13522...

It is different in Africa, where catalytic converters are harvested for precious metals and cars are driven without them.

Is that true for slower moving vehicles? I can't imagine there's a lot of brake dust generated by stopping & starting in the 0-10 mph range.

How do EVs fare in this regard? Brakes are used significantly less, but the additional weight from the batteries chews through tires faster.

It always surprises me when people want stop signs in their neighborhood for traffic calming. The last thing I want is all of the noise and pollution of vehicles stopping and starting over and over again; surely various piece of road furniture like bulb-outs, roundabouts, etc, do a better job with fewer drawbacks. Other than cost, of course.

There are some early tyre and brake dust collection systems which might help, but that won't do much for the road dust.

I've been wondering whether, theoretically, if self driving cars become widely usable and deployed in cities, will they be able to safely operate with harder tyre compounds and harder road surfaces that shed less but don't grip as well?

If nothing else, less aggressive driving should lead to less shedding.

I wonder if it is the `congestion` itself that causes the PM2.5 spike. More stop and go traffic, more brake dust, more tire dust?

Congestion leads to more use of the brakes, which can have nonlinear effects.

Also, I thought tire particles tend to be larger.

There’s also ammonia from farmland, it reacts to form secondary PM25

co2, co, NO.

Nothing i would breath in a garage. Nothing i like to breath in while i'm driving.

This is actually a major nitpick. If this "study" is this sloppy, what else isn't quite true?

  Minor nitpick, but tailpipes aren't the primary source of emissions. 

And besides, even if lung cancer and heart attack may be the most common means of premature death, it does not entail that air pollution is the primary cause of them. I thought that smoking and bad dietary/exercise habits were the main factors. Please correct me if I'm wrong, I'd like to know.