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${{O}{2}}). This N{{O}{2}} absorbs energy from sunlight and breaks up into nitric oxide and free oxygen atom.
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Oxygen atoms are very reactive and can combine with the {{O}{2}} of the air to produce ozone.
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The ozone formed in the above reaction (H) reacts rapidly with the NO(g) formed in reaction (i) to regenerate N{{O}{2}}. N{{O}{2}}is a brown gas and at sufficiently high levels can contribute to haze.
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Ozone is a toxic gas and both N{{O}{2}} and {{O}{2}} are ) strong oxidising agents and can react with the unburnt hydrocabrons in the polluted air to produce chemicals such as formaldehyde (HCHO), acrolein C{{H}{2}}$ = CHCHO) and peroxyacety nitrate (PAN).
