Le Bras and Platt (1995) have assessed the ozone depletion caused by CIO and BrO. We will consider the following reactions. Halogen photolysis: Br+ hv Br + Br Cl+ hv CI+CI Reactions with ozone: Br + 03 BrO + 0 CI+03 CIO + 0 k3 = 7x103 cm molee s k4= 1x10- cm molee s- Regeneration of halogen atoms by reactions with NO: BrO + NO Br + NO ks =2.5x10 cm molec" s CIO + NO CI+NO k6=2x10 cm molec s BrO self-reaction also leads to a catalytic ozone loss cycle: Bro+ BrO 2Br + 0 k7= 3.2x10-2 cm molec" s Br + 03 BrO + 0 ks = 710-2 cm molec-g- ks = 1.2x10-2 cm molec- s ksc = 9x10-2 cm molec" s CIO+ BrO Cl +Br + 0 BrC1 + 0 Br + OCIO The products BrCl and OCIO easily photolyse: BrCl + hv Br+ CI OCIO + hy 0+ CIO TBCI= 53 s Tocio = 6 s (RI) (R2) Sum: 0 + 0 02 +02 + 0 (CIO self-reaction leads to the dimer ClO2 and does not directly produce Cl atoms). A mixed cycle can also occur: (R3) (R4) c) Show that the steady-state ratio of [CIO] and [CI] is given by [CIO]/[CI]= (k4[03])/(ko[NO] +(ksa + ks)[BrO]} (R5) (R6) (R7) (R3) (R8a) (R8b) (R8c) (R9) (R10) a) Show that R3 and R7 lead to the overall reaction 203 30 b) Show that reaction R8c does not lead to net loss of odd oxygen, and that the ozone loss caused by reactions R8a and R8b is: -d[03]/dt = 2(ksa + ksb)[BrO][CIO]