Also discussed here: Estimation of the contribution of road traffic emissions to particulate matter concentrations from field measurements: A review(abstract, Pallavi Pant, Roy M. Harrison, Atmospheric Environment, Oct. 2013)
And here: ‘Only a third’ of traffic pollution caused by exhaust(Air Quality news, Jun. 5, 2013)
Today we review research that carefully estimated what portion of outdoor air pollution comes from vehicle tail pipes and other sources. The answer is that nearly half of the pollution comes from a variety of sources other than exhaust, including brake wear, road wear and dust and particles thrown into the air by passing vehicles. This in turn points the need for corrective action to these secondary sources, by developing less polluting tires and constructing roads better and as well as standards to apply to them, as well as to vehicle emissions.
“it can be concluded that while traffic emissions continue to contribute substantially to primary PM emissions in urban areas, quantitative knowledge of the contribution, especially of non-exhaust emissions to PM concentrations remain inadequate.”
“the emission sources for 82% of the total PM10 mass inside the tunnel. Identified sources include resuspension (27%), diesel exhaust emissions (21%), petrol exhaust emissions (12%), brake wear emissions (11%) and road surface wear (11%).”
“nearly half of the air pollution from road traffic is down to non-exhaust sources such as brake-wear, road surface-wear, and particles launched into the air from the road by passing vehicles.”
“In terms of mass, non-exhaust sources can be more important than exhaust fumes, but legislative control has focussed on exhaust emissions."
“As exhaust regulations become stricter, non-exhaust sources become proportionately more important. Continuing to control exhaust emissions alone may not be enough to achieve legal air-quality standards.”
“Where possible, new technologies and other pollution reduction options should be investigated. These might include, for example, new materials for tyres and brakes and different methods for constructing road surfaces.”