B+-+CFC+and+ozone+layer

=Why is the ozone layer still deteriorating despite the banning of chlorofluorocarbons(CFCs)?=

**Chlorofluorocarbons (CFCs)**

 * ======a type of organic compound that contains carbon, chlorine and fluorine======
 * ======used in aerosols, refrigerators, air conditioners in homes, vehicles and businesses, fire extinguishers, insulating foams, and styrofoam food packaging ======
 * ======marketed as Freon by DuPont and most common ones are trichlorofluoromethane (CFC-11) and dichlorodifluoromethane (CFC-12)======
 * ======highly effective refrigerants because they are ready to be converted between gas and liquid easily: each conversion either absorbs or releases energy (heat)======
 * ======safe to use because they are nonflammable, noncorrosive, nontoxic, nonreactive and odorless======
 * ======banned in the 1990s due to their environmental threats to the ozone layer======

How does CFCs affect the ozone layer?

 * ======When CFCs are released in the atmosphere, the following reaction occurs:======
 * ======After ozone is converted into oxygen, it is not able to absorb UV rays anymore======
 * ======Each chlorine radical can initiate and catalyze a reaction which can break down over 100,000 ozone molecules!======

Why is ozone layer so important to us?

 * ======ozone layer is a layer contains high concentration of ozone ( O3  ) located in the lower portion of stratosphere ======
 * ====== this layer absorbs 97% to 99% of the ultraviolet rays from the sun ======
 * ====== even a relatively small decrease in the concentration of ozone layer can cause a significantly large increased incidence of skin cancer and genetic damage ======

Why is ozone layer still depleting despite the banning of CFCs?

 * ====== CFCs have long lifetime which is about 50 to 100 years ======
 * ====== too many CFCs have been emitted over the past decades and these molecules are still reacting with ozone in the atmosphere ======
 * ====== there are lots of other free radical catalysts which can deplete the ozone layer, such as nitric oxide(NO), nitrous oxide (N2O), hydroxyl(OH), and atomic bromine(Br)   ======
 * ======these catalysts undergo reactions and convert ozone into oxygen gas or atomic oxygen======

Some interesting facts:

 * ======  Freon was replaced by R-134a which is 1,1,1,2-tetrafluoroethane   ======
 * ======  in 2009, the largest ozone depleting substance emitted by human activities was nitrous oxide   ======