Personal exposure of street canyon intersection users to PM2.5, ultrafine particle counts and carbon monoxide in Central London, UK

Short-term human exposure to PM2.5, ultrafine particle counts (particle range: 0.02–1 μm) and carbon monoxide (CO) was investigated at and around a street canyon intersection in Central London, UK. During a four-week field campaign, groups of four volunteers collected samples at three timings (morning, lunch and afternoon), along two different routes (a heavily trafficked route and a backstreet route) via five modes of transport (walking, cycling, bus, car and taxi). 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. Three hundred and ninety-four samples were collected—197 PM2.5, 86 ultrafine particle count and 111 CO. Arithmetic means of PM2.5 personal exposure were 27.5, 33.5, 34.5, 38.0 and 41.5 μg m−3, ultrafine particle counts were 67 773, 93 968, 101 364, 99 736 and 87 545 pt cm−3 and CO levels were 0.9, 1.1, 0.8, 1.3 and 1.1 ppm for walking, cycling, bus, car and taxi respectively. On the heavily trafficked route, personal exposure was 35.3 μg m−3, 101142 pt cm−3 and 1.3 ppm, and on the backstreet route it was 31.8 μg m−3, 71628 pt cm−3 and 0.6 ppm for PM2.5, ultrafine particle counts and CO, respectively. Personal exposure levels were high during the morning measurements for all three pollutants (34.6 μg m−3, 106 270 pt cm−3 and 1.5 ppm for PM2.5, ultrafine particle counts and CO, respectively).There was a moderately strong correlation between personal exposure of ultrafine particle counts and CO (r=0.7, N=67) but a weaker correlation between PM2.5 and ultrafine particle counts (r=0.5, N=83) and a low correlation between PM2.5 and CO exposure (r=0.2, N=105). The exposure assessment also revealed that the background and kerbside monitoring stations were not representative of the personal exposure of individuals to PM2.5 and CO at and around a street canyon intersection.