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Ozone Depleting Substances and Fluorinated Greenhouse Gases

Introduction

Chlorofluorocarbons (CFCs), along with other chlorine- and bromine-containing compounds, have been implicated in the accelerated depletion of ozone in the Earth's stratosphere. These substances are known as Ozone Depleting Substances ODS . CFCs were developed in the early 1930s and are used in a variety of industrial, commercial, and household applications. These substances are non-toxic, non-flammable, and non-reactive with other chemical compounds. These desirable safety characteristics, along with their stable thermodynamic properties, make them ideal for many applications--as coolants for commercial and home refrigeration units, aerosol propellants, electronic cleaning solvents, and blowing agents. Production and Use of CFCs experienced nearly uninterrupted growth as demand for products requiring their use continued to rise.


Global monitoring of ozone levels from space has shown statistically significant downward trends in ozone at all latitudes outside the tropics. Measurements at several ground-based stations have shown corresponding upward trends in CFCs in both the northern and southern hemisphere. Despite rapid phase-out of CFCs, ozone levels are expected to be lower than pre-depletion levels for several decades due to the long tropospheric lifetimes of CFCs. These compounds are carried into the stratosphere, where they can undergo hundreds of catalytic cycles involving ozone before being scavenged by other chemical species.


Replacement compounds for CFCs have also been evaluated for their Ozone Depletion Potential (ODP).Hydrochlorofluorocarbons (HCFCs) still contain chlorine atoms, but the presence of hydrogen makes them reactive with chemical species in the troposphere. This greatly reduces the prospects of the chlorine reaching the stratosphere, as chlorine will be removed by chemical processes in the lower atmosphere.  Hydro fluorocarbons (HFCs), which contain no chlorine, have been slowly been phased in as non ozone depleting replacements for ODSs in several applications. These replacement substances however have a Global Warming Potential (GWP) (Link to definition page)  and  thus also require control with regards to emissions, use and disposal.