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Sequential Measurement of Intermodal Variability in Public Transportation PM and CO Exposure Concentrations 2.5
Wenwei Che, H. Christopher Frey, and Alexis K. H. Lau Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b01594 • Publication Date (Web): 16 May 2016 Downloaded from http://pubs.acs.org on June 4, 2016
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Environmental Science & Technology
SEQUENTIAL MEASUREMENT OF INTERMODAL VARIABILITY IN PUBLIC TRANSPORTATION PM2.5 AND CO EXPOSURE CONCENTRATIONS
W. W. Che,1 H. Christopher Frey,1,2,3 Alexis K.H. Lau1,2,* 1
Division of Environment, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China 2 Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China 3 Department of Civil, Construction and Environmental Engineering, North Carolina State University, Campus Box 7908, Raleigh, North Carolina 27695-7908, United States
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ABSTRACT A sequential measurement method is demonstrated for quantifying the variability in exposure
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concentration during public transportation. This method was applied in Hong Kong by
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measuring PM2.5 and CO concentrations along a route connecting 13 transportation-related
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microenvironments within three-to-four hours. The study design takes into account ventilation,
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proximity to local sources, area-wide air quality and meteorological conditions. Portable
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instruments were compacted into a backpack to facilitate measurement under crowded
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transportation conditions and to quantify personal exposure by sampling at nose level. The route
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included stops next to three roadside monitors to enable comparison of fixed site and exposure
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concentrations. PM2.5 exposure concentrations were correlated with the roadside monitors,
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despite differences in averaging time, detection method and sampling location. Although highly
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correlated in temporal trend, PM2.5 concentrations vary significantly among microenvironments,
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with mean concentration ratios versus roadside monitor ranging from 0.5 for MTR train to 1.3
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for bus terminal. Measured inter-run variability provides insight regarding the sample size
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needed to discriminate between microenvironments with increased statistical significance. The
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study results illustrate the utility of sequential measurement of microenvironments and policy-
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relevant insights for exposure mitigation and management.
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KEYWORDS
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Exposure, transportation mode, fine particulate matter (PM2.5), carbon monoxide (CO)
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Environmental Science & Technology
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INTRODUCTION
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Numerous epidemiological studies have demonstrated associations between traffic-related air
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pollution exposure and a variety of adverse human health effects, including cardiopulmonary
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mortality, respiratory mortality, chronic bronchitis, asthma attacks, low birth weight, and
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childhood respiratory symptoms1-5 Exposure related to transport has been recognized as a key
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target for public-health action in many places.4,6-8
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Public transportation is extensively used in modern cities.9-11 Hong Kong is an example of a city
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heavily reliant on public transport. In Hong Kong, 12 million public transport passenger journeys
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are made daily, of which 41% are by Mass Transit Railway (MTR), a subway system, 32% are
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via diesel-fueled single- or double-decker buses, 15% are via liquefied petroleum gas (LPG)
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public minibuses, and 2% are by tram.12 People spend on average one to two hours daily in
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transit.13-14 Exposure during public transportation may contribute to a significant fraction of daily
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exposure.
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Roadside fixed-site monitors are an indicator of traffic-related exposure. Such monitors are
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placed closed to traffic emission, and can provide measurement data with instruments of high
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precision and accuracy.15-18 A statistically significant high correlation of 0.92 was observed
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between pedestrian PM2.5 exposure and ambient concentration recorded by a roadside monitor in
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Bangkok.18 However, studies conducted in Europe indicate that a roadside monitor can be a poor 3
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indicator of personal exposure to PM (r
