NITRIC-ACID (HNO3) IN THE UPPER TROPOSPHERE AND LOWER STRATOSPHERE ATMIDLATITUDES - NEW RESULTS FROM AIRCRAFT-BASED MASS-SPECTROMETRIC MEASUREMENTS

Extensive measurements of gaseous nitric acid (HNO3) have been perform ed in the upper troposphere and lower stratosphere using aircraft-base d ion-molecule reaction mass spectrometry (IMRMS), The measurements, w hich took place in summer and winter between November 1994 and July 19 96, cover latitudes between 29 degrees N and 57 degrees N and altitude s between 5.5 and 13 km. According to meteorological analyses, potenti al vorticity values up to 9.5 PVU (1 PVU = 10(-6) m(2) s(-1) K kg(-1)) were reached. Stratospheric HNO3 mixing ratios ranged between 300 and 2200 parts per trillion by volume (pptv). In the upper troposphere, n itric acid mixing ratios ranged between 100 and 2000 pptv, with the la rgest values influenced by fast vertical transport from the planetary boundary layer. These values exceed previous measurements and model ca lculations. The relatively high upper tropospheric nitric acid mixing ratio indicates a large rate for NOx recycling from gaseous nitric aci d, and possibly also an increased efficiency of aerosol activation, wh ich may lead to an increased albedo of cirrus clouds.