Hydrochlorofluorocarbons (HCFCs) have been adopted as replacement products forthe chlorofluorocarbons (CFCs), which were banned by the Montreal protocol becauseof their harmful effect on the ozone layer. In contrast to the CFCs, the HCFCs can beoxidized in the troposphere, and the oxidation products washed out by precipitation, sothat most of the HCFCs do not penetrate into the stratosphere to destroy ozone. Twocommon HCFCs have trade names HCFC-123 and HCFC-124; their lifetimes againstoxidation in the troposphere are 1.4 years and 5.9 years, respectively. There are noother sinks for these species in the troposphere. Using our 2-box model, determinewhat fractions of the emitted HCFC-123 and HCFC-124 penetrate the stratosphere.