NOx and CO Fluctuations in a Busy Street Canyon

Busy street canyons can have a large flow of vehicles and reduced air exchange wind speeds at level, exposing pedestrians to high pollutant concentrations. The airflow tended move with along the canyon 1-s concentrations NO, NO2 CO were highly skewed close road more normally distributed sensors some metres above road. pollutants autocorrelated these elevated sensors, suggesting less variable concentration away from traffic in areas low turbulence. kerbside also showed cyclic changes approximating nearby signal timing. cross-correlation between measurements suggested that variation moved vehicle speed canyon, but slower vertically. NOx slightly higher under metre per second. local ozone had little effect on proportion present as NO2. Pedestrians roadside would be unlikely exceed USEPA hourly guideline value for 100 ppb. Across campaign period, individual minutes exceeded guidelines, though short-term, high-concentration exposures is not well understood. Tram stops carriageway divider are places where longer levels traffic-associated possible.