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Spatial distribution of diesel transit bus emissions and urban populations: implications of coincidence and scale on exposure.

Authors
  • Gouge, Brian
  • Ries, Francis J
  • Dowlatabadi, Hadi
Type
Published Article
Journal
Environmental Science & Technology
Publisher
American Chemical Society (ACS)
Publication Date
Sep 15, 2010
Volume
44
Issue
18
Pages
7163–7168
Identifiers
DOI: 10.1021/es101391r
PMID: 20715793
Source
Medline
License
Unknown

Abstract

Macroscale emissions modeling approaches have been widely applied in impact assessments of mobile source emissions. However, these approaches poorly characterize the spatial distribution of emissions and have been shown to underestimate emissions of some pollutants. To quantify the implications of these limitations on exposure assessments, CO, NO(X), and HC emissions from diesel transit buses were estimated at 50 m intervals along a bus rapid transit route using a microscale emissions modeling approach. The impacted population around the route was estimated using census, pedestrian count and transit ridership data. Emissions exhibited significant spatial variability. In intervals near major intersections and bus stops, emissions were 1.6-3.0 times higher than average. The coincidence of these emission hot spots and peaks in pedestrian populations resulted in a 20-40% increase in exposure compared to estimates that assumed homogeneous spatial distributions of emissions and/or populations along the route. An additional 19-30% increase in exposure resulted from the underestimate of CO and NO(X) emissions by macroscale modeling approaches. The results of this study indicate that macroscale modeling approaches underestimate exposure due to poor characterization of the influence of vehicle activity on the spatial distribution of emissions and total emissions.

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