Factors affecting variability in PM2.5 exposure concentrations in a metro system

摘要

The objectives of this study were to: (1) evaluate PM_(2.5) inflow to metro train cabins when doors open at stations; (2) assess the spatial and temporal variability in PM_(2.5) exposure concentration; and (3) quantify the relationship between in-cabin concentration versus outdoor and non-ambient PM_(2.5). We measured in-cabin PM_(2.5) concentrations using portable monitors at the door-side and center of a train cabin simultaneously on a Hong Kong metro line. In addition, platform and in-cabin pollutant concentrations near a train door were simultaneously measured. Short-term spikes in PM_(2.5) concentrations typically occur near train doors when doors open, related to inflow of ambient air aboveground and tunnel air underground. In-cabin PM_(2.5) exposure concentrations are typically lower away from the doors when the doors open. PM_(2.5) concentrations inside train cabins and on station platform operating above-ground are more influenced, compared to underground, by outdoor PM_(2.5). Moreover, non-ambient sources contribute approximately 50% of train in-cabin and station platform PM_(2.5) concentrations during underground operation. The results help more accurately quantify commuting PM_(2.5) exposure on a metro system, and can be used to improve population-based exposure simulation models.