Field study of wind and traffic to test a street canyon pollution model

In the U.K., local authorities have new duties to review and assess air qua lity. Dispersion models are important tools in this process. The performanc e of a street canyon model, AEOLIUS, in calculating carbon monoxide (CO) co ncentrations in urban areas is discussed. A field experiment was conducted in a busy street canyon in Leek, Staffordshire. Wind speed and direction we re measured at three heights adjacent to the street. The canyon's CO concen trations and traffic counts were recorded. Predicted concentrations of CO, calculated using AEOLIUS, were compared with the observed values. The concept of a 'roof-top' wind is discussed, as are the consequences of u sing wind measurements from outside the town. Choice of wind measurement lo cation and height of the anemometer above the canyon had a pronounced effec t on calculating the 'roof-top' wind. Two methods of deriving a street leve l wind speed from a 'roof-top' wind speed gave results that differ by up to a factor of two. AEOLIUS had variable skill at predicting CO concentration s depending on the 'roof-top' wind direction: possible reasons for this var iability are explored. A sensitivity study of the model showed that vehicle emissions have the greatest impact on predicted concentrations. Implicatio ns for local air quality management are discussed.