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Development and application of traffic density-based parameters for studying near-road air pollutant exposure
Citation:
Liu, S., J. Xue, AND F. Chen. Development and application of traffic density-based parameters for studying near-road air pollutant exposure. ISES 2016, Utrecht, NETHERLANDS, October 09 - 13, 2016.
Impact/Purpose:
Traffic density-based parameters may be more specific indicators than conventional traffic indicators for near-road exposure to air pollutants from mobile source emissions and may be useful in assessing traffic contribution to health risk on human populations living and/or working in near-road environments.
Description:
Increasingly human populations are living and/or working in close proximity to heavily travelled roadways. There is a growing body of research indicating a variety of health conditions are adversely affected by near-road air pollutants. To reliably estimate the health risk associated with near-road air pollutants, one of the greatest challenges is accurately understanding exposures in these microenvironments because actual monitoring data on the air pollutants are often not available. To overcome this limitation, we performed a metadata analysis on data compiled from literature search and obtained from EPA-sponsored measurement studies to evaluate air pollutants’ concentration decay rate (R) which equals Ln (Ca/Ci) / D where Ci and Ca represents concentration initially and after a distance (D), respectively. We also compared correlation of near-road air pollutants’ concentrations with conventional traffic indicators such as nearest distance (ND) to major road and total length (TL) of major road as well as three traffic density-based indicators we developed: Major-Road Density (MRD), All-Traffic Density (ATD) and Heavy-Traffic Density (HTD). Our metadata analysis yielded mean decay rates (fraction of concentration decrease per meter) for black carbon (BC), carbon monoxide (CO), nitrogen dioxide (NO2) and nitrogen oxides (NOX) as 0.0026, 0.0019, 0.0004, and 0.0027, respectively, while no such decay was noticeable for particulate matter (PM). Traffic density-based indicators MRD, ATD) and HTD yielded respective average correlation coefficients of 0.26, 0.18 and 0.48 for BC measured in the Near-road Exposures and Effects of Urban Air Pollutants Study (NEXUS). In contrast, average correlation coefficients of -0.31 and 0.25 were generated for BC when considering its relationship to two commonly used traffic indicators: ND and TL. Further analysis of MRD and ATD with ambient concentration data for ozone (O3), CO, NOx, sulfur dioxide (SO2), lead (Pb), and PM retrieved from US Environmental Protection Agency (EPA)’s Aerometric Information Retrieval System (AIRS) showed correlation coefficients in range of 0.22 to 0.47 for the mobile source related pollutants CO and NOX but less than 0.19 for O3, SO2, Pb, and PM. Thus, the traffic density-based parameters may be more specific indicators than conventional traffic indicators for near-road exposure to air pollutants from mobile source emissions and may be useful in assessing traffic contribution to health risk on human populations living and/or working in near-road environments.
