Increases in radiation exposure of <1 mrad/yr due to gaseous effluents from a nuclear facility can be measured using sensitive high pressure ionization chambers. As a result of the rapidly fluctuating nature of the plume exposure rate contributions compared to the normal background signal, increases in exposure due to gaseous effluents can be uniquely distinguished from variations in ambient background. Passive devices such as thermoluminescent and film dosimeters are incapable of routinely measuring perturbations of this magnitude and, moreover, provide no mechanism for identifying the cause of an increase in integrated exposure. Collateral in situ gamma spectrometry has been used to verify the natural exposure rate levels, to identify the isotopes in the gaseous effluent, to estimate off-gas holdup times, and to investigate the exposure from 16N in the steam turbines of a boiling water reactor (BWR) plant.