Aims/background Particulate air pollution from fossil fuel combustion is associated with impaired lung growth. In highly polluted cities there may be a health benefit in avoiding high particulate exposures. We sought to measure which modes of urban transport result in the lowest exposure of black carbon (soot) exposure to individuals.
Method An aethalometer (MicroAeth AE51) was used to measure black carbon (BC) mass per minute. A standard route was devised between Whitechapel and Westminster using different modes of transport (walking, bus and underground railway). Total exposure (ng per m3/min) and exposure “peaks” (events exceeding 10000 ng per m3/min) were calculated for each mode of transport. Results were compared by Mann-Whitney U test.
Results Total BC exposure is highest on the underground (16020 (12647–27451) ng per m3/min, median (IQR)) relative to walking (4053 (2980–6825) ng per m3/min) and buses (5466 (4497–6184) ng per m3/min, *p = 0.02, Kruskal Wallis test with Dunn’s multiple comparisons, Figure 1). There was no significant difference in mean BC exposure between walking and bus use. Number of exposure “peaks” was significantly higher on the underground compared to bus, with median 23 (15–36) peaks vs 2 (0.25–4.5), and 35 (6–45) for walking (p < 0.05 underground vs bus, Kruskal Wallis test with Dunn’s multiple comparisons, n = 4 journeys on each mode of transport).
Conclusion Particulate exposures are highest on underground transport in comparison to buses or walking on this route. Exposures to high peaks of black carbon are decreased while on a bus. Children and families may wish to take particulate exposure into account when planning how to move around highly polluted urban environments. The particles in overground air are well characterised but work is needed on the origin and health effects on growing lungs of black particles in the underground.