Effect of near-IR photolysis of HO2NO2 on stratospheric chemistry -: art. no. 1223

[1] We use a 3D model to assess the impact of the recently reported near-IR (NIR) photolysis of HO2NO2 on global stratospheric chemistry. Including this process in the model leads to a significant reduction in HO2NO2 for all latitudes and seasons. The effect is larger at high latitudes with the maximum reduction (>95% near 20 km) in winter. While the basic model strongly overestimates the MIPAS balloon observations of HO2NO2 at mid-high latitudes, this discrepancy is largely removed by including the NIR photolysis. In high latitude winter below 25 km the model still overestimates HO2NO2 but this may be due to remaining uncertainties in HO2NO2 formation/loss rates and modelled NO2. The NIR photolysis increases model HOx (OH + HO2). At high latitudes around 18 km HOx increases by over 30% all-year-round, with much larger enhancements (>70%) near the terminator. However, there is a corresponding NOx (NO + NO2) decrease of similar to10% in high latitude summer. Consequently, at this altitude O-3 decreases by only 1 - 2%.