An aircraft mounted system is described which permits the measurement of concentrations of Aitken nuclei in the stratosphere at altitudes up to 20 km. An automatic cycling cloud chamber, with a dark field optical system and photomultiplier detector, is used to analyze 2.5 samples/sec. A pressurization system is incorporated which standardizes ambient air samples to approximately 1 atm absolute pressure and 298 K temperature before analysis. Seven successful data flights have been accomplished in the period Marchndash;May 1974.
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