Exposure to PM2.5, Black Carbon and ultrafine particles in above- and underground public transport.

Abstract

Background: Several studies have shown that particulate matter (PM) concentrations in underground public transport areas such as subway stations are substantially higher compared to outdoor situations. Little is known about how these levels compare to similar above ground locations. Aims: To assess exposure to PM2.5, Black Carbon (BC) and particle number concentrations (PNC) in underground and above ground train and subway transport. Methods: Concentrations of PM2.5, BC and PNC in public transport were measured in two cities in the Netherlands (Amsterdam and Rotterdam) using real-time monitors. In each city, a 3 hour route was traveled twice for 5 non-consecutive days. Each route included at least 15 minutes measurement time in each of the following 8 site categories: underground and above ground train stations, underground and above ground subway stations, underground and above ground trains, and underground and above ground subway vehicles. Results: Concentrations of PM2.5 and BC were significantly higher in each of the four underground site categories compared to the above ground locations. The highest average BC and PM2.5 concentrations were observed in underground train stations (9 and 71 ?g/m3 respectively). BC showed the largest contrasts between sites: Concentrations at underground train stations were 5 times higher compared to above ground levels, and were also 3 times higher compared to levels inside underground train and subway vehicles. Inside vehicles, strong increases and decreases in concentrations were observed when entering or exiting tunnels, and concentrations increased with increasing length of the tunnel. PNC was only significantly elevated at the underground train stations. We estimated that 2 daily 15 minutes commutes in the underground results in an extra daily exposure of 0.35 ?g/m3 (3%) for PM2.5, and 0.06 ?g/m3 (6%) for BC. Conclusion: We found significantly elevated levels of BC and PM2.5 in underground transport locations.