Investigation of a river-tunnel effect on PM concentrations in New York City subway stations.

It is well-documented that subway stations exhibit high fine particulate matter (PM) concentrations. Little is known about the potential of river-tunnels to increase PM concentrations in subways. We hypothesized a "river-tunnel" effect exists: Stations adjacent to poorly ventilated tunnels that travel beneath rivers exhibit higher PM concentrations than more distant stations. Accordingly, the PM concentrations were monitored at stations adjacent to and two- and three-stations distant from the river-tunnel. Multivariate linear regression analysis was conducted to disentangle how proximity to a river-tunnel and other factors (e.g., depth) influence concentrations. Stations adjacent to a river-tunnel had 80-130% higher PM concentrations than more distant stations. Moreover, distance from a river-tunnel was the strongest PM-influencing factor This distance effect was not observed at underground stations adjacent to a river-bridge. The "river-tunnel" effect explains some of the inter-station variability in subway PM concentrations. These results support the need for improving ventilation systems in subways.