Aitken Particle and Cloud Condensation Nucleus Fluxes in the Plume from an Isolated Industrial Source

Abstract

Measurements in the plume from an isolated copper and lead smelting operation in northeastern Australia have been made from an aircraft to a distance of 560 km from the source. The aim was to gain information on the composition, numbers and sizes of cloud condensation nuclei (CCN) emitted by this very strong source, with a view to later relating this information to the differences in properties between clouds affected and unaffected by the plume. In the cloudless, inversion-limited conditions of the winter months the particulate plume retained a coherent, easily detected shape out to the largest distance worked, 560 km downwind of the source at which point the plume was 260 km wide. The Aitken particle flux ranged from ?2 ? 1018 s?1, measured between 56 and 185 km downwind, to >1019 s?1 at distances >370 km downwind. The increase in flux and changes in the size distribution of particles collected from the plume as a function of distance downwind suggest that gas-phase oxidation of sulphur dioxide in the plume leads to nucleation of new particles as the plume disperses. Knowledge of the size distribution and chemical composition of the particles enabled CCN concentrations to be calculated. In this way the flux of CCN active at 0.5% supersaturation (S) was estimated to range from a minimum of ?5 ? 1017 s?1 at 90 km downwind to ?5 ? 1018 s?1 at 500 km downwind. This latter figure is thought to equal ?0.1% of the global, natural production rate of particles active at 0.5% S.