Heterogeneous chemistry and the O-3 budget in the lower mid-latitude stratosphere

A photochemical box model including a detailed heterogeneous chemistry modu le has been used to analyze in detail the effects of temperature and aeroso l surface area on odd oxygen production/depletion in the lower stratosphere at 30 degrees S. Results show that for background aerosol loading, the hyd rolysis of BrONO2 and N2O5 are most important at all temperatures studied e xcept when the temperature falls below about 205 K, when ClONO2 hydrolysis becomes most important. This processing leads to removal of active nitrogen to form nitric acid and enhancement of HOx, BrOx, ClOx levels. Detailed O- 3 budgets as a function of temperature are presented showing how ozone loss and production terms vary with changes in stratospheric sulfate aerosol lo ading for the individual families. For (most) aerosol loading levels, the l argest ozone losses occurred at warmer temperatures due to the strong tempe rature dependence of the NOx ozone-destroying reactions. The exception to t his occurred for the conditions representative of volcanic loading, which s howed a strong increase in ozone destruction due to increases in destructio n from the ClOx and HOx families. The ozone production term k[NO][HO2] did not show a strong dependence on either temperature or aerosol loading, due to the offsetting effect of reduced NOx and increased HOx concentrations.