Pedestrian exposure to air pollution along a major road in Central London, UK

Pedestrian exposure to PM2.5, the loss of reflectance (‘blackness’) of the PM2.5 filters, ultrafine particle counts (particle range: 0.02–1 μm) and carbon monoxide (CO) was investigated along a major road running through the DAPPLE study site in Central London, UK. During an intensive 12-day exposure measurement campaign, groups of four volunteers sampled twice in the morning and twice in the afternoon along Marylebone Road. They were randomly designated a walking direction, walking position (kerbside or buildingside) and a side of the major road to walk along. PM2.5 was sampled using high-flow gravimetric personal samplers, ultrafine particle counts were measured using TSI P-TRAKs and Langans were used to measure CO exposure. PM2.5 samples were analysed gravimetrically and reflectance was measured using a smoke stain reflectometer to obtain a measure of ‘black smoke’. In total 603 acceptable samples were obtained—155 PM2.5 and reflectance, 120 ultrafine particle count and 173 CO. The average pedestrian exposure along the road was 37.7 μg/m3, 12.1 m−1×10−5, 80 009 pt/cm3 and 1.3 ppm for PM2.5, loss of reflectance, ultrafine particle counts and CO, respectively. PM2.5 exposure in the morning was significantly higher than in the afternoon, and there was a significant difference in exposure on the different sides of the road. For both reflectance and ultrafine particle counts, the exposure was significantly different both between the two walking positions on the pavement and the two sides of the street canyon. However there was no significant difference in CO exposure based on walking position, walking direction, canyon side or timing. Filter reflectance was significantly but weakly correlated with PM2.5 exposure (r=0.3r=0.3, N=155N=155), CO exposure (r=0.2r=0.2, N=154N=154) and ultrafine particle count exposure (r=0.7r=0.7, N=108N=108). PM2.5 and CO personal exposure measurements were much higher than those recorded at both the local background fixed monitoring station (FMS) and a kerbside FMS, but PM2.5 personal exposure was significantly correlated with the PM2.5 concentrations at the background FMS (r=0.6r=0.6, N=155N=155).