Most local air pollution, counterintuitively, doesn't even come from exhaust. Wear on tires, brakes, and the road each contribute more individually. There's a

Most local air pollution, counterintuitively, doesn't even come from exhaust. Wear on tires, brakes, and the road each contribute more individually. There's another process called resuspension that dwarfs even these. Cars grind down large particles sitting on the road, making heavy particles light enough to float in the air. Then the cars' wake kicks those newly light particles into the air, suspending them in the air. That process is driven by vehicle weight, size, and aerodynamics, and contributes about two-thirds of the particulates from all vehicle sources. One of the interesting takeaways from all that is that average vehicle weight can be massively important to local air conditions (no pun intended). I think there's still some debate about the exact relationship between weight to PM output, but lighter frames and smaller vehicles are probably a good idea: http://www.greencarcongress.com/2016/04/20160418-pm10.html http://www.greencarcongress.com/2016/04/20160418-pm10.html