Synoptic weather evolution and climate drivers associated with winter air pollution in New Zealand

Particulate matter pollution of less than 10 μm in diameter (PM10) is a problem for some regional and urban centres across New Zealand during the winter period when solid fuel (wood and coal) fires are used for home heating. Elevated levels of PM10 concentrations occur during stable atmospheric conditions, when cool air temperatures and low wind speeds allow for a surface inversion to occur and trap PM10. This study examined the relationships between PM10 and local and large-scale synoptic conditions at daily and seasonal scales. Minimum temperature and wind speed were both negatively correlated with PM10 during the winter season, whilst the combination of the two can explain 30-54% of variability in average PM10. Synoptic-scale daily composites of high PM10 days showed the evolution of an anticyclone in the Tasman Sea, with an injection of cool air over New Zealand and persistent south-westerly winds leading to cold and stable conditions on the day of exceedance. Both of these results indicate that there is some potential for predicting days in which atmospheric conditions could favour elevated PM10 concentrations. Furthermore, at the seasonal scale, weaker westerly winds were found to be associated with winters with higher exceedance days, although the relationship is not straightforward. These characteristics can be associated with other, predictable large-scale climate drivers such as the El Niño-Southern Oscillation, and may aid in identifying years in which a higher risk of PM10 pollution events exists.