A modelling study of participate matter dispersion under dominant surface wind regime modes in Christchurch, New Zealand

摘要

Prognostic air pollution models such as TAPM are used to study air pollution on multi-day to multi-seasonal scales, driven by daily synoptic forcings. In complex terrain, mesoscale regimes can introduce diurnally reversing wind systems that can be persistent features of low level climatology - especially during stagnant anti-cyclonic conditions that result in deterioration of air quality. In this study, TAPM is modified to ignore synoptic forcings yet still produce terrain induced flows that are common features over the Canterbury Plains in New Zealand. In addition, surface-based climatology for two different regimes is assimilated into the model in order to study their effects on temporal evolution of PM10. Two common modes of surface wind conditions are observed in Christchurch during evenings of high pollution days where the national guideline for PM1Q is exceeded. Low level flow during the evening hours with generally low wind speeds is dominated by either a north-westerly or a south-westerly wind direction. Results from TAPM simulations of dispersion indicate north-easterly flow opposes north-westerly to westerly drainage flow from the Southern Alps and traps pollutants over the city for an increased period of time and therewith delays flushing by a few hours. Simulated pollution levels during the evening are close to observed values and indicate that atmospheric control mechanisms are simulated well. This study delivers a viable tool for local environmental monitoring authorities to estimate generalised spatiotemporal pollution behaviour under different low level flow conditions.