RAINWATER ACIDITY AT JABIRU, AUSTRALIA, IN THE WET SEASON OF 1983/84

Rainwater was collected on an event basis at Jabiru, Australia (12°40′S, 132°53′E), from 20 October 1983 till 28 March 1984. Analysis showed that rainwater in this area contained only about 20 μeq 1-1 each of major cations and anions. However, the rainfall was acidic (volume weighted mean pH 4.89). The free acidity was due mostly to the presence of formic acid and other unidentified weak organic acids, although sulfuric, nitric and hydrochloric acids made significant contributions, especially early in the Wet season. A strong meteorological influence on ion concentration was evident in the consistent decrease in concentration associated with the change in storm classification from transitional to monsoonal. Concentrations of sulfur dioxide, aerosol sulfate and cloudwater sulfate due to emissions from the Mount Isa smelting complex 1200 km distant were calculated according to a simple dispersion model used previously in Australian plume studies. The calculations suggest that Mt Isa would contribute little to atmospheric acidity at Jabiru under the normal range of meteorological conditions in the region. © 1990.