Acid rain studies in Australia and New Zealand

Abstract

This paper reviews the results of the few scattered acid rain studies in Australia and New Zealand. Large scale spatial discussions are not possible, so discussion, focussing on wet deposition, is limited to rainwater acidity and chemistry on a regional and local basis. Rainwater samples were mainly collected on a daily or event basis, and some attempt was made to ensure contamination from dry fallout in all cases. Rainwater acidity can be divided into three regimes: non-tropical urban, non-tropical rural and tropical rural areas with the Tropic of Capricorn the dividing line between tropical and non-tropical. In Sydney, representative of non-tropical urban, local emissions of acid gases, particularly sulphate and nitrate, resulted in an average pH of 4.4. At several non-tropical rural locations, pHs average between 5.0 and 5.7, indicative of global background levels. Tropical rural pHs average about 4.5, due mainly to natural acidity caused by vegetation release of volatile organic acids. These values indicate that rainwater in this region contains from 2 to 12 times less acidity than in the northern hemisphere where acid rain is a problem. Rainwater chemistry is dominated by ocean influences along the coast and soil and vegetation influences inland. Elevated levels of sulphate and nitrate in rainfall of the Latrobe Valley and the Hunter Valley may be due to power station and industrial sources located there, but do not prove to be a problem.