Post Date: 7 March 2016

Variation of commuter exposure to air pollutants in transport microenvironments in Hong Kong

Abstract

Historically, approaches for monitoring air pollution generally use expensive, complex, stationary equipment, which cannot capture spatial gradients in the regions for which they are representative. This paradigm is changing with the rapid development of low-cost, easy-to-use, small, and portable air quality monitoring sensors that provide high spatiotemporal resolution data. Recently, the use of portable sensors in personal exposure monitoring have emerged in order to accurately quantify the exposure levels. First, the methods used for the evaluation and calibration of DustTrak Aerosol Monitor Model 8530 and Q-Trak Indoor Air Quality Monitor Model 7565 (TSI Inc., Shoreview, MN) are introduced. Then, the sampling design, data collection, and data processing and analysis of the public transport exposure study, which is to evaluate the variability of commuter exposure to air pollutants in transport microenvironments in Hong Kong, are presented. PM_2.5 concentrations are sensitive to transport microenvironments, and are affected by factors such as seasons and proximity to on-road emission sources. In general, Mass Transit Railway (MTR) train in-cabin (above-ground) has higher PM_2.5 concentrations than other microenvironments. CO₂ concentrations in the vehicle in-cabin microenvironments can be as high as several thousand ppm, and CO concentrations are the highest at the bus stop and bus in-cabin microenvironments. The differences between PM_2.5 concentrations in transport microenvironments and data from nearby air quality monitoring stations (AQMS) indicate that the AQMS data cannot be readily applied to estimate commuter exposures. In addition, source apportionment result shows that MTR-related source contributes about half of the included PM species. Future investigations will be conducted to examine how air pollutants especially PM_2.5 vary when people commuting inside the MTR trains considering that the MTR system transports approximately 5 million commuters/day in Hong Kong.