THE SENSITIVITY OF THE RADICAL AMPLIFIER TO AMBIENT WATER-VAPOR

The radical amplifier is an instrument used to measure radical concent rations in the troposphere. The critical parameter in determining the sensitivity is the chain length, which is shown to decrease with incre asing water vapour in the reactor. When compared to measurements in dr y air, this decrease is a factor 2 at a relative humidity of 40%. This suggests that field measurements using the radical amplifier may be u nderestimating the ambient radical concentration by a similar factor. One source of this deterioration in performance is an increase in the loss of radicals to the walls of the reactor, although there also appe ars to be a contribution from a water dependence on the gas phase chem istry.