On the logarithmic relationship between NO2 concentration and the distance from a highroad

Measurements of nitrogen dioxide (NO2) concentrations, performed with passive diffusion samplers in gradients from a highway in South-west Sweden, were used to test the assumption that the NO2 concentration contributed by the highway varies with the logarithm of the distance from the highway. The five data sets used corroborated the hypothesis, and it was shown that all data could be accommodated to a common relationship with high correlation (R2=0.95) using the concentration of 10 m away from the highroad as the reference. The data were also well in accordance with a recently published study from Canada, although the slope of the relationship between the NO2 concentration contributed by a highway and the logarithm of the distance was somewhat stronger for the Swedish data compared to the Canadian. The regression slope is likely to be sensitive to wind speed, atmospheric stability, surface roughness and the background ozone concentrations of the area.