Mass spectrometry in the stratosphere

Abstract During the last few years a gas expansion system, combined with a mass spectrometer has been developed and successfully flown in the stratosphere. Neutral gas particles are formed into a molecular beam which traverses the ion source of the mass spectrometer without wall interactions. Vertical profiles of constituents such as H 2 O, CO 2 and O 3 have been measured in the altitude range of 20 to 40 km during balloon descents. Isotopes of major atmospheric gases (N 2 , O 2 , Ar) provided in-flight calibration standards. Before each flight the mass spectrometer system was calibrated in the laboratory for many gases of interest, including ozone. Mixing ratios of ozone determined from recent flights have accuracies of better than 5%. The sensitivity of the system was sufficiently high to detect, in addition, the heavy isotope of ozone at mass 50. A pronounced enhancement of heavy ozone in the upper stratosphere has been found. The mass spectrometer system provides the unique opportunity to perform in the stratosphere in-situ measurements combined with isotopic studies.