A very high resolution infrared solar spectrometer system for the Network for Detection of Stratospheric Change has been routinely operated at the Mauna Loa Observatory in Hawaii since November, 1991. Solar absorption spectra are normally taken one day a week at sunrise. We report the analysis of these spectra for the vertical column amount of nitric acid (HNO3) vapor. The observations began four months after the arrival of volcanic aerosols from Mt. Pinatubo over the site. Although quite variable, total HNO3 columns were initially about 7¿1015 molecules/cm2 and have decreased about 30% in the following two years. ¿ American Geophysical Union 1994