Modelling wintertime PM10 dispersion in Masterton, New Zealand:: a tool for implementing national standards

The National Environmental Standards (NES) for air quality have recently been introduced in New Zealand (NZ). Many urban areas experience high levels of PM10 and compliance with the regulations for concentrations of PM10 and other pollutants must be achieved by 2013. This study uses urban airshed modelling techniques as a tool for assessing effects of pollution mitigation options. Masterton is a rural town with regular exceedences of the PM10 standard over winter, due largely to emissions from wood burning for home heating. A simulation of PM10 dispersion in Masterton for the winter months of 2003 has been carried out using TAPM (Version 3) on nested horizontal grids, down to 1 km spacing for meteorology and 0.5 km for pollution. Statistical measures of model performance show that the model performs well for both meteorology and pollution. The model links concentrations and emissions, showing an approximately linear relationship between them, although the number of exceedences is expected to decrease an approximate 15% reduction of domestic emissions has been achieved. The results demonstrate that modelling can be a useful tool for assessing emission reduction scenarios for NES compliance. Urban airshed modelling is a challenging task in coastal regions or complex terrain (typical of most NZ cities), particularly for regulatory purposes due to the requirement of simulation for extended periods at high temporal and spatial resolution. In addition, for small towns like Masterton, airshed modelling is a new technique. Therefore, this study represents a significant step forward for the application of airshed modelling in NZ and elsewhere.