As exhaust emissions of particles and volatile organic compounds (VOC) from road vehicles have 40 progressively come under greater control, non-exhaust emissions have become an increasing 41 proportion of the total emissions, and in many countries now exceed exhaust emissions. Non-42 exhaust particle emissions arise from abrasion of the brakes and tyres and wear of the road surface, 43 as well as from resuspension of road dusts. The national emissions, particle size distributions and 44 chemical composition of each of these sources is reviewed. Most estimates of airborne 45 concentrations derive from the use of chemical tracers of specific emissions; the tracers and 46 airborne concentrations estimated from their use are considered. Particle size distributions have 47 been measured both in the laboratory and in field studies, and generally show particles to be in both 48 the coarse (PM2.5-10) and fine (PM2.5) fractions, with a larger proportion in the former. The 49 introduction of battery electric vehicles is concluded to have only a small effect on overall road 50 traffic particle emissions. Approaches to numerical modelling of non-exhaust particles in the 51 atmosphere are reviewed. Abatement measures include engineering controls, especially for brake 52 wear, improved materials (e.g. for tyre wear) and road surface cleaning and dust suppressants for 53 resuspension. Emissions from solvents in screen wash and de-icers now dominate VOC emissions 54 from traffic in the UK, and exhibit a very different composition to exhaust VOC emissions. Likely 55 future trends in non-exhaust particle emissions are described.
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