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

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.