Fig. 4.

a) Concentration (χ) vs. downwind distance (x/H), both normalized, for receptor heights within the breathing level. Cases shown are the No Barrier case (0 m), and Barrier cases with the barrier located at either the upwind edge (Up) or downwind edge (Down) of the roadway and with either a 4.5 m or 6 m barrier height. When present, the downwind barrier is located at x/H = 0 and the upwind barrier is located at x/H = −6. Dots show the measured concentrations in the wind tunnel within the breathing level, and the spread of these observations are shown by the shading of the smoothed lines (95% confidence interval). Note that H = 6 m (length scale). b) Plot omitting the receptor locations at x/H = −5.875, −3, −0.125, which are close to the upwind edge of the roadway, center of the roadway, and close to the downwind edge of the roadway, respectively