Quality of the Auckland airshed

Abstract

Identification and understanding of the main contributory factors to degraded air quality in Auckland has become an important research field in recent years. The present research was to achieve two main outcomes: improving understanding of the relationship between meteorological conditions and air quality, and identifying the potential effect of land use on the quality of the regional airshed, in an effort to assist with future air quality management in Auckland. Although the research was limited to one city, the results are valuable for improving the conceptual understanding of formation of high urban pollution in a more general sense in the New Zealand and wider contexts. Analyses were performed on three inter-related themes: local meteorology-air quality relationships, land use-air quality relationships, and the relationships between synoptic weather types, local meteorology and air quality. The assessment was focused on winter months and on nitrogen oxides (NO and NO2). Multivariate approaches using statistical techniques such as principal component and cluster analyses were applied to air quality studies for the first time in New Zealand. The approaches have allowed for the analyses to be conducted in an integrated framework, and proved powerful and successful. The air quality in Auckland varied significant from site to site; the effects of meteorological conditions on air quality were significant, but differed between pollutants and for different emission source conditions. The inter-site variability of air quality was attributable to the differences in land use characteristics and hence emissions from areas surrounding the air quality monitoring sites, and the effects of meteorological conditions. The difference in the role of meteorological conditions for different pollutants may be due to influences of such factors as chemical processes. A strong correlation between land use and air quality was identified. A synoptic climatological index was established for the Auckland region (and New Zealand) for winter months (May-September) from 1958-1996. The weather types were linked to distinctive local meteorological conditions, and subsequently, to different air quality in Auckland. It was indicated that, when using a synoptic approach to air quality problems within urban regions, it is important to consider the effects of differences in land use (and thus emissions) surrounding a monitoring site, in order to seek a physically meaningful evaluation of the weather impacts on air quality. The the weather type-local meteorology relationships were consistent over time, regardless of occurrences of climatic phenomena such as ENSO events and New Zealand climate shift; significant changes in the frequencies of some synoptic weather types were identified, corresponding to ENSO events. Implications and applications of the findings were discussed, and limitations of the study and future directions also addressed.