Stratospheric aerosol sulfuric acid: First direct in situ measurements using a novel balloon-based mass spectrometer apparatus

The first direct in situ measurements of the sulfuric acid contained in stratospheric aerosol particles were made using a novel balloon-based Ion Molecule Reaction Mass Spectrometer instrument (IMRMS) equipped with an aerosol vaporizer. The IMRMS method employed offers direct aerosol sulfuric acid measurements with high spatial resolution. The balloon flight took place on 23 October 1995 in middle latitudes (44 degrees N) and reached a maximum altitude of 24 km. Measured molecular number densities of aerosol sulfuric acid decreased with increasing altitude from about 2.9 x 10(9)cm(-3) at 15 km altitude to about 2.4 x 10(8)cm(-3) at 21 km. Corresponding mass mixing ratios are 2.5 and 0.6 ppbm, respectively. Calculated sulfuric acid mixing ratios from aerosol volumes inferred from aerosol size distribution measurements on the same balloon agree well with the IMRMS data using standard assumption aerosol composition.