Which of the following statements is not correct?

• A
  Catalytic converters present in automobiles prevent the release of nitrogen oxide to the atmosphere.
• B
  Photochemical smog is a mixture of smoke,fog and $SO_2$.
• C
  Chlorofluorocarbons damage ozone layer.
• D
  Acid rain corrodes water pipes resulting in the leaching of heavy metals into the drinking water.