Science Objectives: Nitrogen Dioxide, Nitrogen Trixoide, and Chlorine Dioxide

Nitrogen dioxide (NO2), nitrogen trixoide (NO3), and chlorine dioxide (OClO) play crucial roles in stratospheric chemistry and the catalytic cycles that destroy stratospheric ozone. SAGE III measurements will provide important contributions in the following areas:

• SAGE III NO2 measurements are important because the processes that occur in the Antarctic winter and spring and give rise to the ozone hole effectively convert NO2 to nitric acid (HNO3). Thus NO2 is an important diagnostic of ozone hole chemistry.

• Since it is measured during both solar and lunar occultation events, SAGE III observations of NO2 will improve our understanding of the strong diurnal (daily) cycles in stratospheric processes.

• SAGE III will make virtually unique measurements of nitrogen trixoide (NO3). Although it is short lived in the presence of sunlight, NO3 plays an active role in the chemistry of other reactive nitrogen species such as NO2 and di-nitrogen pentoxide (N2O5) and, thus, indirectly in ozone chemistry.

• Since few other measurements of NO3 are available, SAGE III measurements, which are made during lunar occultation (nighttime) events, will provide crucial validation for our current understanding of reactive nitrogen chemistry.

• The unique SAGE III observations of chlorine dioxide (OClO) will provide insight into nocturnal polar chemical processes that set the stage for the ozone loss observed at high latitudes in the spring.