The findings of Sanders et al. (2003) appear strongly supported in the recent study of Iijima et al. (2007). Dynamometer tests were conducted on three non-steel brake lining materials to generate abrasion dusts, across a range of temperatures simulating different driving conditions and braking severity. Number size distributions measured using an Aerodynamic Particle Sizing (APS) instrument revealed a peak mode of 1–2 µm in all tests. Mass size distributions were calculated from number size distributions, and indicated peak particle emissions in the range 3–6 µm. The authors estimated between 74% and 92% of brake wear particles, by number, to be emitted as PM2.5, corresponding to 12–36% of particle mass. The highest proportions of PM2.5 emissions were found in the lower temperature tests, considered to be representative of urban driving cycles. These findings highlight the great variability that can be anticipated in brake wear emissions under real-world conditions, and the strong dependency on vehicle operating conditions. Differences between the conclusions of Iijima et al. (2007) and the earlier work of Garg et al. (2000) may be explicable in terms of differences in experimental set-ups and lining materials tested.Mosleh et al. (2004) characterised brake wear particles using a laser scattering method and concluded that wear debris tends to show a bimodal particle number size distribution. A peak in the fine particle fraction around 350 nm was identified in all the brake tests performed, independent of brake pressure or lining material. A second mode was seen in