15min:

J. A. PHILLIPS, UCAR / NOAA Postdoctoral Research Fellow in Climate and Global Change, Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309; V. VAIDA, Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309.

In the atmosphere, HNO₃ is an important reservoir species for the odd nitrogen (NO_x) and odd hydrogen (HO_x) families, both of which contribute to the destruction of stratospheric ozone. In the sunlit atmosphere, NO₂ and OH are liberated by photolysis of HNO₃. Therefore, in order to model the distribution of these species, accurate values for the photodissociation cross section of HNO₃ are necessary, particularly for wavelengths beyond 290 nm, which dominate the available light in the lower stratosphere. Previous investigations show significant discrepancies at wavelengths greater than 310 nm, and have also noted a marked temperature dependence in this region. In an effort to resolve these discrepancies, and determine if clusters of HNO₃ are affecting the previous measurements, we have reexamined the near UV absorbance cross section from 240 to 350 nm at a wide range of pressures and temperatures. Implications of these results for the observed diurnal variation of [OH] in the lower stratosphere will be discussed.