Vertical Profiles of Particulate Matter Size Distributions during Winter Domestic Burning in Christchurch, NZ

This study describes the application of a novel technique for obtaining vertical profiles (0-400m AGL) of PM size distributions in a highly polluted setting dominated by domestic burning of wood and coal. At night, smoke from domestic fires is emitted into a highly stable and shallow katabatic flow layer. This layer is only ~20-40m in depth and gives rise to very high concentrations that may persist late into the night. The mass size distribution of wood/coal smoke in Christchurch is overwhelmingly dominated by fine particles (<1ìm in aerodynamic diameter). The vertical profiles reveal that layers of pollutants (with distinct PM signatures) may be found in such wintertime nocturnal settings. In Christchurch (population ~400,000) a dominant mechanism appears to be undercutting by shallow drainage flows. This creates elevated layers with a daytime surface PM signature (predominately coarse material with modes at 2.5 and 6.25 ìm). These results confirm the usefulness of the deployment of miniature optical PM instruments on tethered balloons in cool, humid, polluted conditions. Such measurements allow the proper evaluation of the current generation of air pollution dispersion models.