Effect of varying wind direction on exhaust gas dilution

Abstract The influence of changing wind direction on the dilution of exhaust gases around buildings was investigated in a simulated, neutrally stable atmospheric boundary layer using a low speed, open circuit wind tunnel. Mean concentration measurements were made on six flat-roofed model buildings at 2–5 wind incidence angles of between 0 and 45°. When vertical exhaust momentum was low, dilution levels 2–8 times lower (depending on building shapes and vent location) were observed for wind incidence angles >30°. However, at high exhaust momentum, the minimum dilution lost its sensitivity to wind direction. A semi-empirical model was devised to quantify, within a factor of 2, the dependence of minimum dilution on wind incidence angle and exhaust momentum.