Development of a distance-to-roadway proximity metric to compare near-road pollutant levels to a central site monitor |
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| Authors: | Timothy M Barzyk Barbara Jane George Alan F Vette Ronald W Williams Carry W Croghan Carvin D Stevens |
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| Institution: | 1. Applied Physics Department, School of Aeronautic and Space Engineering, Universidade de Vigo, As Lagoas s/n, Ourense 32004, Spain;2. Computer Science Department, School of Informatics (ESEI), Universidade de Vigo, As Lagoas s/n, Ourense 32004 Spain;1. School of Environment & Sustainability and Toxicology Centre, University of Saskatchewan, 44 Campus Drive, Saskatoon, SK, S7N 5B3, Canada;2. Institute for Environmental Research, RWTH Aachen University, Worringerweg 1, 52074 Aachen, Germany;3. Department of Veterinary Biomedical Sciences and Toxicology Centre, University of Saskatchewan, 44 Campus Drive, SK S7N 5B3 Saskatoon, Canada;4. Department of Zoology and Center for Integrative Toxicology, Michigan State University, East Lansing, MI, USA;5. School of Biological Sciences, University of Hong Kong, Kowloon, Hong Kong, SAR, China;6. College of Resources and Environmental Science, Chongqing University, 1 Tiansheng Road Beibei, Chongqing 400715, China;7. College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai, China;8. State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, 1239 Siping Road, Shanghai, China;9. State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, China |
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| Abstract: | The primary objective of the Detroit Exposure and Aerosol Research Study (DEARS) was to compare air pollutant concentrations measured at various neighborhoods, or exposure monitoring areas (EMAs), throughout a major metropolitan area to levels measured at a central site or community monitor. One of the EMAs was located near a busy freeway (annual average daily traffic (AADT) of ～130,000) so that impacts of mobile sources could be examined. Air pollution concentrations from the roadway-proximate sites were compared to the central site monitor. The volatile organic compounds (VOCs) selected (benzene, toluene, ethylbenzene, m,p- and o-xylene, 1,3 butadiene, 1,3,5-trimethylbenzene and 4-ethyltoluene) are typically associated with mobile sources. Gradients were also evident that demonstrated the amplification of pollutant levels near the roadway compared to the community monitor. A novel distance-to-roadway proximity metric was developed to plot the measurements and model these gradients. Effective distance represents the actual distance an air parcel travels from the middle of a roadway to a site and varies as a function of wind direction, whereas perpendicular distance is a fixed distance oriented normal to the roadway. Perpendicular distance is often used as a proxy for exposures to traffic emissions in epidemiological studies.Elevated concentrations of all the compounds were found for both a summer and winter season. Effective distance was found to be a statistically significant (p < 0.05) univariate predictor for concentrations of toluene, ethylbenzene, m,p-xylene and o-xylene for summer 2005. For each of these pollutants, effective distance yielded lower p-values than the corresponding perpendicular distance models, and model fit improved. Results demonstrate that this near-road EMA had elevated levels of traffic-related VOCs compared to the community monitor, and that effective distance was a more accurate predictor of the degree to which they were elevated as a function of distance. Effective distance produced a range of distance-to-roadway values for a single site based on wind direction, thus increasing the number and range of values that could be used to plot and predict relative differences in pollutant concentrations between two sites. |
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