REVIEW 2 General comment:

The manuscript is generally well written, easy to follow and the subject matter falls well within the scope of ACP. The affects on O3 RF are indeed significant and merit further work on this subject, but the experiments themselves are, in general, not novel (the same parameterization for this reaction already being used in the study by Cariolle et al. [2008]). My major criticism of this work is in the parameterization of the HNO3 forming channel of the HO2 + NO reaction, which (as stated in the on-line comment by Dr J.-F. Müller) does not take into account the H2O dependence that the reaction has been shown to exhibit (Butkovskaya et al. 2009). The importance of the HO2-H2O adduct on reactions such as the HO2 + HO2 reaction has been included in models for many years now. In this manuscript the authors should also investigate the importance of the HO2-H2O adduct on the HO2 + NO reaction. This work would also greatly benefit from detailed analysis of the global (tropospheric and stratospheric) O3 and NOy budgets. The affects that the O3 reductions have on the methane lifetime also need to be more quantitatively discussed. After consideration of these comments and those below, I feel this work will be suitable for publication in ACP. Reply: The comment by Dr J.-F. Müller is well taken. As pointed out by G. Le Bras (online comment S