Ambient nitrogen dioxide and distance from a major highway

The primary objective of this pilot study was to measure the variation of ambient nitrogen dioxide (NO2) concentration with increasing distance from a major highway in Montréal, Canada, in order to assess the validity of distance from the roadways as a surrogate for exposure to traffic-related air pollution in epidemiologic studies. A total of 31 two-sided Ogawa™ passive samplers (using triethanolamine-impregnated filters as an absorbent) were installed for 7 days in groups of two or three along an axis perpendicular to a major highway where traffic density exceeds 100 000 vehicles/day. Distances ranged from 0 to 1310 m from the highway. Concentrations of NO2 ranged from 11.9 to 29.3 ppb, and decreased significantly with increasing logarithmic distance from the highway (P<0.0001). Concentrations of NO2 were also significantly lower upwind than downwind relative to the highway (P=0.0012). These findings indicate that distance from highways may be a valid surrogate for traffic-related air pollution.