Abstract:
During the winters of 2010 and 2011, three intensive particulate matter (PM) monitoring campaigns were undertaken in Masterton, Alexandra and Nelson, New Zealand. The goal of these campaigns was, for the first time, to identify the sources and factors contributing to elevated PM concentrations on an hourly time-scale. In each location, hourly coarse (PM₁₀-₂.₅; particles with aerodynamic diameters 2.5 μm < d < 10 μm) and fine (PM₂.₅; particles with aerodynamic diameters < 2.5 μm) samples, PM₁₀ (particles with aerodynamic diameters < 10 μm, incorporating the coarse and fine fractions) concentrations and meteorological variables were collected from a number of sites. Using elemental concentrations determined from ion beam analysis and black carbon concentrations determined from light reflection for each hourly sample, PM sources and their contributions on an hourly time-scale were identified using positive matrix factorization (PMF).
In Masterton, where two sampling sites were employed, PM₁₀ concentrations displayed distinct diurnal cycles, with peak concentrations occurring in the evening (7 pm–midnight) and in the morning (7–9 am). Four PM sources were identified (biomass burning, marine aerosol, crustal matter and vehicles) at each of the sites and biomass burning was identified as the most dominant source of PM₁₀ during both the evening and morning. One of the sites experienced consistently higher PM₁₀ concentrations and katabatic flows across Masterton were identified to be the main contributor to this phenomenon.
In Alexandra and Nelson, three sampling sites on a horizontal transect (upwind, central and downwind of the general katabatic flow pathway) and a fourth site located centrally, but at a height of 26 m, were incorporated in a novel study design. Each of the sites in Alexandra and Nelson also showed diurnal patterns in PM₁₀ concentrations. The central site in Alexandra experienced consistently higher PM₁₀ concentrations and four PM₁₀ sources were identified at each of the sites (biomass burning, marine aerosol, vehicles and crustal matter). Biomass burning was identified as the main source of PM₁₀ throughout the day at each of the sites. The convergence of numerous katabatic flows was identified as the contributing factor to the elevated PM₁₀ concentrations measured at the central site.
In Nelson, five PM sources were identified at each of the sites (biomass burning, vehicles, marine aerosol, shipping sulfate and crustal matter) and biomass burning was identified as the dominant source of PM₁₀ throughout the day. Katabatic flows were also identified to play an important role in PM₁₀ transport.
Analyses of source-specific (wood combustion and vehicles) PM samples was also undertaken, and the results of these analyses are included in this thesis.
