Ground-based measurements of NO3 column abundance over Table Mtn, California

The nitrate radical, NO3, which is being monitored by Meteosat/SAGE III, is an important intermediate in the transformation of NOx to NOy. Better characterization of the diurnal, seasonal and interannual variation of NO3 is important in characterizing the role of NOx-catalyzed ozone depletion in the stratosphere. In this work the nighttime variation of the NO3 column abundance has been studied over Table Mountain, California beginning in June 2002 We collected lunar occultation data around full moon with a grating spectrograph which utilized a CCD detector. NO3 column abundances were retrieved from lunar spectra using the differential optical absorption spectroscopy (DOAS) technique. A significant problem in the retrieval is the interference of water vapor and O2 in the NO3 visible absorption bands. To minimize these interferences, retrievals were carried out on both the 662 and 623 nm NO3 bands. Comparisons between the observed nighttime temporal profiles of NO3 and the predictions of a one-dimensional photochemical model will be discussed.