Relative Efficiencies of Filters and Impactors for Collecting Stratospheric Particulate Matter

The relative efficiencies of impactors of the type used by Junge and co-workers for collecting stratosphere sulfate particles and of filters used in these laboratories have been determined by flying these collecting devices on the same aircraft in the stratosphere. The impactors have less than 20% of the efficiency of the filters for total sulfate. At most, a small percentage of the stratospheric sulfate was present as the ammonium salt. At least about half of the ammonium ion found on the impactors could have resulted from reaction of the collected samples with ammonia in tropospheric air.