HCFCs, chemical species slated to replace CFCs in the near future in most Western nations. When the normal chlorofluorocarbons (see above) reach the stratosphere and are photo-decomposed, their released chlorine radicals destroy the natural ozone that acts as our umbrella to shield the Earth from ultraviolet radiation (see chlorine and ozone). With one or more hydrogen-carbon bonds, HCFCs are still useful as replacement for CFCs in most applications. However, this bonding structure makes HCFCs much more chemically unstable--as compared to CFCs--and therefore subject to hydroxyl radical and ozone attack early in their gas phase career in the atmosphere. In fact they react in the troposphere instead of the stratosphere. Their atmospheric lifetime is shorter than CFCs and they, therefore, have a smaller chance of reaching the stratosphere where their chlorine could be released by destructive photolysis and enter the catalytic ozone destruction cycle.