Write down the reactions involved during the formation of photochemical smog



When fossil fuels are burnt, a variety of pollutants | are emitted into the earth’s troposphere. Two of | the pollutants that are emitted are hydrocarbons (unburnt fuels) and nitric oxide (NO). When these j pollutants build up to suffidently high levels, a I chain reaction occurs from their interaction with sunlight in which NO is converted to nitrogen | dioxide (N${{O}{2}}$). This N${{O}{2}}$ absorbs energy from sunlight and breaks up into nitric oxide and free oxygen atom.

Oxygen atoms are very reactive and can combine with the ${{O}{2}}$ of the air to produce ozone.

The ozone formed in the above reaction (H) reacts rapidly with the NO(g) formed in reaction (i) to regenerate N${{O}
{2}}$. N${{O}{2}}$is a brown gas and at sufficiently high levels can contribute to haze.

Ozone is a toxic gas and both N${{O}
{2}}$ and ${{O}{2}}$ are ) strong oxidising agents and can react with the unburnt hydrocabrons in the polluted air to produce chemicals such as formaldehyde (HCHO), acrolein C${{H}{2}}$ = CHCHO) and peroxyacety nitrate (PAN).