Dispersion Modeling in Canterbury Airsheds: Can it Play a Useful Role in Policy Formation of Urban Air Quality Management?
Air quality in New Zealand is primarily managed through national environmental standards, national guidelines, and regional policy frameworks. For most urban airsheds the primarily focus is the management of PM10, although a few airsheds have issues with NO2 and SO2 contaminants. Regional Councils that are tasked with the management of air quality have a range of policy tools in terms of their plans, rules, emission inventories, education and other economic incentives to reduce PM10 emissions. One tool that has not been widely used to date in New Zealand is the use of dispersion modeling of whole urban airsheds to guide policy formation of PM10 reduction. This paper describes the process of developing and testing the CALMET-CALPUFF modeling system for six urban areas in Canterbury, South Island. The study forms part of Environment Canterbury (local regional council) initiative to test various policy initiatives with the CALPUFF modeling system. Various setups of CALMET with different upper air data from diagnostic and prognostic sources, domain grid configurations were processed and run for the respective urban areas. The different CALMET data was used to model urban airsheds for the six towns. Predicted CALPUFF 24-hour PM10 concentrations generally show good agreement with ambient monitoring data for five of the six urban areas but poor agreement with the number of exceedences of the 50 μg/m3 standard. It was concluded that the over prediction of exceedences relates to the over use of worst-case emission assumptions. Implications for policy development are discussed in the paper.