Further assessment of the atmospheric controls on night-time air pollution dispersion in Alexandra, Central Otago, New Zealand from idealized modelling experiments

摘要

This research uses observational data and idealized sensitivity runs using a regional atmospheric model to further characterize the atmospheric controls on air pollution dispersion in the Alexandra Basin (Central Otago, New Zealand), with a focus on the mechanisms responsible for the bi-modal evening peak that has been observed in Alexandra. As a first step we demonstrate clearly that the variability in night-time air pollution is unique to Alexandra and is not typical of other small towns in the region. Atmospheric modelling is then used to show that air pollution from Clyde, another township in the Alexandra Basin, does not contribute significantly to the observed air pollution in Alexandra, and cannot be responsible for the bi-modal evening peak. The variability in evening air pollution is controlled by the strength and direction of local drainage winds, in particular from the south-east in the early evening. Importantly, the idealized modelling allows us to distinguish between the effects of large scale atmospheric processes and local drainage winds on the dispersion of air pollution. Enhanced vertical mixing of the near surface atmosphere for 7-8 hours is effective at dispersing air pollution during the daytime, but atmospheric stability does not appear to be the primary control on variability in air quality in the evening. To completely resolve the observed changes in air pollution in Alexandra further measurements of its spatial and temporal variability are still required, and will be necessary if new and effective solutions to improve air quality of the township are to be established in the future.