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A complex interplay of chemistry, dynamics, and radiation lead to conditions conducive to significant ozone loss in the Polar Regions. The sequence of events leading to the springtime depletion of ozone is initiated by the onset of polar night, when high latitude regions receive no sunlight. The inclination of the Earth's orbit at about 23.5degrees causes the Polar Regions to experience continual darkness during their winter season. The air above the pole cools and a vortex is formed that isolates the colder region from the lower latitudes.  Creation of the vortex sets the stage for the rapid depletion of ozone by catalytic cycles. A catalytic cycle is a series of reactions in which a chemical family or a particular species is depleted, leaving the catalyst unaffected. The odd-oxygen family, for example, is composed of ozone (O₃) and atomic oxygen (O). In the presence of a chlorine atom, the net result is the conversion of an oxygen atom and ozone molecule to two molecules of molecular oxygen (O₂). Chlorofluorocarbons (CFCs) themselves are not involved in the catalytic process; upon reaching the stratosphere, they are subject to higher levels of ultraviolet radiation that decompose the CFC and release atomic chlorine. The basic set of reactions that define the catalytic cycle involving chlorine and odd-oxygen appear as: Cl + O3 → ClO + O₂; ClO + O → Cl + O₂; Net result: O3 + O → 2O₂.

Chlorine (Cl) is initially removed by reaction with ozone to form chlorine monoxide (ClO) in the first step, but it is regenerated through reaction of ClO with an oxygen atom (O) in the second step. The net result of the two reactions is the depletion of ozone and atomic oxygen. Multiphase reactions involving aerosol particles are another source of ozone loss that can occur at all latitudes.  Increasing chlorofluorocarbon (CFC) levels and subsequent depletion of stratospheric ozone has led to calls for alternative substances having a lower propensity for ozone destruction. Two main classes of replacement compounds have been developed: hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). HCFCs still contain chlorine atoms that are responsible for catalytic destruction of ozone, but they also contain hydrogen, which makes them vulnerable to reaction with hydroxyl radicals (OH) in the lower atmosphere. Removal of these substances in the troposphere reduces the amount of chlorine reaching the stratosphere, where significant depletion can occur. HFCs are composed of hydrogen, fluorine, and carbon, and are similarly decomposed in the troposphere.

The scientific community has defined two useful parameters to estimate the potential impact of controlled and replacement substances on ozone destruction: the Ozone Depletion Potential (ODP) and the Chlorine Loading Potential (CLP). ODP is  a measure of the destructive potential of a particular substance relative to depletion caused by an equal amount of a reference substance. CFC-11 is typically defined as the standard reference compound and is assigned an ODP of 1.0. In similar fashion, CLP is defined as the total amount of chlorine contained in a particular compound reaching the stratosphere relative to an equivalent release of CFC-11. A standard value of 1.0 is again assigned as the CLP of CFC-11.   ODP is usually defined as a single, steady-state measure of ozone depletion over the entire lifetime of the substance. Knowledge of tropospheric OH concentration is one of the limiting factors in determining lifetimes of alternative substances and accounts for differing ODP values calculated by various research groups. Because HFCs contain no chlorine, their ODP has been assumed to be zero. But HFCs containing a CF3 group may be sufficiently stable to reach the stratosphere, where fluorine radicals can engage in catalytic destruction of ozone. It has been conclude that the ODP for HFCs containing a CF3 group is negligibly small and constitutes no more of a threat than HFCs and HCFCs that do not contain a CF3 group.   

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