Size distribution and sources of aerosol in Launceston, Australia, during winter 1997

As part of a pilot study into the chemical and physical properties of Austr alian fine particles, a suite of aerosol samples was collected at Ti Tree B end in Launceston, Tasmania, during June and July 1997. This period represe nts midwinter in the Southern Hemisphere, a period when aerosol sources in Launceston are dominated by smoke from domestic wood burning. This paper de scribes the results from this measurement campaign, with the aim of assessi ng the effect of wood smoke on the chemical and physical characteristics of ambient aerosol. A micro orifice uniform deposit impactor (MOUDI) was used to measure the size distributions of the aerosol from 0.05 to 20 mu m aero dynamic diameter. Continuous measurements of fine particle mass were made u sing a PM2.5 tapered element oscillating microbalance (TEOM) and light scat tering coefficients at 530 nm were measured with nephelometers. Mass size distributions tended to be bimodal, with the diameter of the domi nant mode tending to smaller sizes with increases in total mass. Non-sea sa lt potassium and polycyclic aromatic hydrocarbons (PAHs) were used as chemi cal tracers for wood smoke. Wood smoke was found to increase absolute parti cle mass (enough to regularly exceed air quality standards), and to concent rate mass in a single mode below 1 mu m aerodynamic diameter. The acid-base equilibrium of the aerosol was altered by the wood smoke source, with free acidity hydrogen ion, non-sea salt sulfate, and ammonium concentrations be ing higher and the concentration of all species, including nitrate (to diff ering extents), focused in the fine particle size ranges. The wood smoke so urce also heavily influenced the aerosol scattering efficiency, adding to a strong diurnal cycle in both mass concentration and light scattering.