Radon measurements as an aid to the interpretation of atmospheric monitoring

Abstract

Radon has been measured continuously at Cape Grim, Tasmania with a detection limit of about 0.05 Bq m^-3 (1.4 pCi m^-3). The annual average level from a close continental source is 3.8 Bq m^-3, whereas the level in maritime air streams is typically 0.5 Bq m^-3. The contribution of the ocean is about 0.04 Bq m^-3, which indicates that more than 90% of radon in maritime air is from a continent. Thus radon can provide much less equivocal evidence of the degree of continental influence on an air stream than can other atmospheric constituents, whose sources and loss mechanisms are more complex. A knowledge of the past history of an air stream is important in the interpretation of atmospheric measurements.

There is a close correlation between low radon and low Aitken particle concentrations, which suggests a continental origin for these particles. On the basis of present data it is difficult to reconcile this with evidence that the particles are generated photochemically over the ocean. An extension of the radon program to other latitudes would help to resolve this discrepancy.