4. (a) HO cycling can catalyze 03 loss in multiple ways. Consider the reactions below, which are each important in at least some region of the stratosphere. Find five different catalytic 03 loss cycles starting with reaction of OH. Which of the reactions represent sinks for HOx, i.e. are termination steps? OH + 0 + O2 +H OH + HO2 + H2O + O2 OH + O3 HO2 + O2 H + O2 +M HO2+M H+03 02 + OH HO2 + 0 + OH + O2 HO2 + 03 OH + 202 HO2 + HO2 H2O2 + O2 (b) The chemistry below is important in the troposphere. Identify each reaction as initiation, propagation, or termination. HONO + hy OH + NO CH4 + OH + H2O + CH3 CH3 + O2 + CH3O2 CH3O2 + NO + NO2 + CH3O NO2 + OH+M HNO3 +M NO2 + CH3O2 + CH3O2NO2