Particulate matter sources on an hourly timescale in a rural community during the winter

Abstract

Particulate matter (PM) sources at four different monitoring sites in Alexandra, New Zealand, were investigated on an hourly timescale. Three of the sites were located on a horizontal transect, upwind, central, and downwind of the general katabatic flow pathway. The fourth monitoring site was located at the central site, but at a height of 26 m, using a knuckleboom, when wind conditions permitted. Average hourly PM₁₀ (PM with an aerodynamic diameter <10 μm) concentrations in Alexandra showed slightly different diurnal profiles depending on the sampling site location. Each location did, however, feature a large evening peak and smaller morning peak in PM₁₀ concentrations. The central site in Alexandra experienced the highest PM₁₀ concentrations as a result of PM transport along a number of katabatic flow pathways. A significant difference in PM₁₀ concentrations between the central and elevated sites indicated that a shallow inversion layer formed below the elevated site, limiting the vertical dispersion of pollutants. Four PM₁₀ sources were identified at each of the sites: biomass combustion, vehicles, crustal matter, and marine aerosol. Biomass combustion was identified as the most significant source of PM₁₀, contributing up to 91% of the measured PM₁₀. Plots of the average hourly source contributions to each site revealed that biomass combustion was responsible for both the evening and morning peaks in PM₁₀ concentrations observed at each of the sites, suggesting that Alexandra residents were relighting their fires when they rose in the morning. The identification of PM sources on an hourly timescale can have significant implications for air quality management.

Implications: 

Monitoring the sources of PM₁₀ on an hourly timescale at multiple sites within an airshed provides extremely useful information for air quality management. Sources responsible for observed peaks in measured diurnal PM₁₀ concentration profiles can be easily identified and targeted for reduction. Also, hourly PM₁₀ sampling can provide crucial information on the role meteorology plays in the development of elevated PM₁₀ concentrations.

Acknowledgment

The support of Otago Regional Council (Deborah Mills) was greatly appreciated. The authors thank Bruce Crothers and Ed Hutchinson for their support in maintaining the sampling equipment and Chris Purcell for setting up and maintaining the 3-MeV accelerator used for IBA. Stuart Grange is also thanked for his support during sampling.

Funding

This work was funded by the Ministry of Science and Innovation under contract C05X0903.

Supplemental Data

Supplemental data are available for this paper. Go to the publisher’s online edition of the Journal of the Air & Waste Management Association for information containing sampling locations, analytical results, wind and pollution roses, source profiles and source-specific polar plots.

Additional information

Notes on contributors

Travis Ancelet

Travis Ancelet is a scientist, Perry K. Davy and William J. Trompetter are senior scientists, and Andreas Markwitz is a principal scientist at GNS Science in Lower Hutt, New Zealand.

Perry K. Davy

Travis Ancelet is a scientist, Perry K. Davy and William J. Trompetter are senior scientists, and Andreas Markwitz is a principal scientist at GNS Science in Lower Hutt, New Zealand.

William J. Trompetter

Travis Ancelet is a scientist, Perry K. Davy and William J. Trompetter are senior scientists, and Andreas Markwitz is a principal scientist at GNS Science in Lower Hutt, New Zealand.

Andreas Markwitz

Travis Ancelet is a scientist, Perry K. Davy and William J. Trompetter are senior scientists, and Andreas Markwitz is a principal scientist at GNS Science in Lower Hutt, New Zealand.

David C. Weatherburn

David C. Weatherburn is a senior tutor at Victoria University of Wellington in Wellington, New Zealand.