Evaluation of a year-long dispersion modelling of PM10 using the mesoscale model TAPM for Christchurch, New Zealand

This paper examines the utility of The Air Pollution Model (TAPM; version 2) in simulating meteorology and dispersion of PM10 for 1999 over the coastal city of Christchurch, New Zealand. Christchurch usually experiences severe degradation in air quality during austral winter. The formation of a nocturnal inversion layer and the emissions of particulate matter (PM10) mainly from solid fuel home heating appliances lead to severe smog episodes on an average of 30 nights during winter. The complex local topography surrounding the city in combination with influences from the urban areas can produce complicated boundary layer winds during quiescent weather. Simulated PM10 data are used for construction of annual exposure maps for the urban areas in order to assess the health impact of air pollutants due to chronic exposure (presented in an accompanying paper). Meteorology and PM10 dispersion results are statistically compared with the only permanent air pollution monitoring station available in order to evaluate the model's performance. Statistical measures such as the Index of Agreement (IOA) between modelled and measured data indicate that the model performs well. IOA is greater than 0.6 for meteorological variables, and various calculated skill scores place confidence in the model's performance. However, TAPM has a tendency to overestimate surface wind speed over urban areas during stagnant nocturnal conditions, resulting in quick flushing of pollutants.