Spatial variability of fine particulate matter pollution (PM2.5) on the London Underground network

We present the first spatially explicit assessment of passenger exposure to fine particulate matter (PM2.5) across the London Underground transport network. Measurements were made using portable aerosol monitors inside passenger carriages. PM2.5 concentrations were highly variable within Underground tunnels, ranging from 39 μg m−3 to 734 μg m−3 for PM2.5 on the deep tunnel lines and 14 μg m−3 to 368 μg m−3 for PM2.5 on the shallow sub-surface lines. On the deeper lines, PM2.5 concentrations were on average 18-times higher than concentrations at the surface. We also find significant increases in PM2.5 concentrations with distance into the tunnels of the London Underground network. For a commuter spending 1 h per day in underground transit, an incremental increase in daily PM2.5 exposure of 12 μg m−3 is found. These concentrations suggest that further research into potential health effects of underground air pollution are warranted