Abstract
Aerosols were collected during September 1979 at Cape Grim, Tasmania and at Kissing Point, Townsville, Queensland by six-stage single orifice cascade impactors and stacked-filter samplers. The impactor samples were analyzed by PIXE for 18 elements, among them sulfur. The stacked-filter units consisted of a 8 μm Nuclepore prefilter and a Teflon filter which quantitatively collects all the particles passed through the prefilter. The Teflon filters were analyzed by proton elastic scattering analysis (PESA) for the light elements up to potassium. The following elements were detected: C, N, O, Na, Mg, Si, S, Cl, and K. The stoichiometric relationship between carbon and fluorine in the Teflon filter material (CF
2) permits the precise subtraction of the carbon contained in the filter from the carbon in the sample. The detection limit for carbon is 0.08 μ m
−3 air.
Two airmass types were observed at Cape Grim: purely marine air during south-westerly flow, which had not made contract with land areas for at least five days, and airmasses from the Australian continent during northerly flow. No fine particle mode is detectable for sulfur during marine conditions; during northerly flow such a mode occurs around 0.5 μm aerodynamic diameter. Good agreement is found between the sulfur analyses on impactors by PIXE and on filters by PESA. Carbon concentrations at Cape Grim are around 0.25 μg m
−3, most of it in the form of organic material. During marine flow no soot carbon is detectable.
At Townsville, a period of continental flow brought large amounts of soot carbon from biomass burning to the sampling site. These carbon concentrations were accompanied by a large increase of fine particle potassium and silica, diagnostic for biomass combustion. A pronounced fine particle mode was evident for sulfur under these conditions. During a subsequent period of onshore flow from the east, this mode was still present in attenuated form. Stoichiometric relationships between sulfur, oxygen and nitrogen in the Townsville samples suggest that the aerosol consists largely of ammonium sulfate.