The influence of highway traffic on ambient nitrogen dioxide concentrations beyond the immediate vicinity of highways

doi:10.1016/j.atmosenv.2006.12.007

Atmospheric Environment

Volume 41, Issue 12, April 2007, Pages 2670-2673

https://doi.org/10.1016/j.atmosenv.2006.12.007 Get rights and content

Abstract

The objective of these analyses was to determine whether highways significantly influence ambient concentrations of NO₂ at distances greater than 200 m. NO₂ was sampled for 14 consecutive days in May 2003 at 67 sites across Montréal, Canada. The association between logarithmic concentrations of NO₂ and land-use variables was assessed using multiple regressions. Locations less than 100 m from the nearest highways were excluded, leaving 61 data points. Then, locations less than 200 m were excluded, leaving 55 data points. Excluding sampling locations located less than 100 or 200 m from the nearest highway did not substantially change the regression parameters. NO₂ was still significantly associated with both the distance from nearest highway and the traffic count on the nearest highway. These findings indicate that the negative association found between distance from highways and NO₂ concentration in several land-use regression studies in Europe and North America was not generated solely by the high concentrations found in the immediate vicinity of highways.

Introduction

Nitrogen dioxide (NO₂) is considered to be an essential marker for traffic-related air pollution. Characterizing its spatial and temporal variability, especially in urban centers, is important in determining whether air pollution may cause adverse health outcomes. Several studies on the spatial variability of ambient NO₂ have found that concentrations were higher near highways and that spatial variability overall was influenced strongly by these high-volume roadways (Rodes and Holland, 1981; Roorda-Knape et al., 1999; Gilbert et al., 2003, Gilbert et al., 2005). However, including NO₂ concentration as a continuous, dependent variable and distance as a continuous, independent variable in regression analysis provided no indication about the maximum distance at which highways influence concentrations of NO₂. More specifically, it does not rule out the possibility that highways have a significant influence on NO₂ concentrations in the immediate vicinity of highways (e.g., within 100 m) and have no influence beyond.

The purpose of the present paper is to determine whether highways significantly influence ambient concentrations of NO₂ at distances greater than 200 m. For this purpose, we analyzed the spatial variability of NO₂ using data from a previous study carried out in Montréal, Canada, by excluding locations less than 100 or 200 m from the nearest highway. In Montreal, highways are expressways with at least two traffic lanes in each direction, and that vehicles access and exit through ramps (i.e., no traffic light). Traffic counts on the highways segments included in this study ranged between 48,000 and 165,000 vehicles day⁻¹.

Section snippets

Methods

The method used for data collection has been described previously (Gilbert et al., 2005). Briefly, NO₂ was sampled in May 2003 at 67 sites across Montréal using two-sided Ogawa™ passive diffusion samplers that were exposed for 14 consecutive days at a height of 2.5 m, and then analyzed by ion chromatography. Linear regression analysis was used to assess the association between logarithmic concentrations of NO₂ and land-use variables derived using the ESRI Arc 8 geographic information system

Results

Table 1 shows the results of standard regression analyses assuming distance could be well represented by a parametric linear function. Excluding sampling locations located at less than 100 or 200 m from the nearest highway did not substantially change the linear regression parameters (Table 1). Moreover, the R², which was 0.545 with all data points, increased to 0.585 after excluding locations within 100 m from a highway, and to 0.602 after excluding locations within 200 m. After excluding

Discussion

Results from this study are consistent with findings from studies of decays of concentrations of NO₂ with increasing distance from highways (Rodes and Holland, 1981; Gilbert et al., 2003), where concentrations of NO₂ declined beyond 200 m from the roadway. More recent land-use regression studies (Jerrett et al., 2007; Gilbert et al., 2005) found that this trend could be observed in sampling locations scattered across a large city, and influenced by different highway segments with various traffic

Acknowledgments

The authors are grateful to Anna-Maria Frescura for assistance in fieldwork, to Sandy Benetti for analyzing NO₂ samples, to Bernardo Beckerman for computing land-use variables, and to Amanda Wheeler and Cheryl Lettner for reviewing an earlier version of this manuscript. Dr. Goldberg gratefully acknowledges receipt of an Investigator Award from the Canadian Institutes for Health Research. This study was supported by Health Canada.

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Short communicationThe influence of highway traffic on ambient nitrogen dioxide concentrations beyond the immediate vicinity of highways