Photochemical smog is the most widely known and perhaps most serious air pollutant. It is formed in the atmosphere by the reaction between gaseous pollutants, nitrogen oxides and hydrocarbons

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Photochemical Smog

Photochemical smog is the most widely known and perhaps most serious air pollutant. It is formed in the atmosphere by the reaction between gaseous pollutants, nitrogen oxides and hydrocarbons in the presence of strong sunlight. These gases are from motor vehicle exhaust and commercial/industrial processes. The two types of pollutants that produce photochemical smog are primary pollutants and secondary pollutants.

Primary pollutants are harmful substances put directly into the air by human activity. The main types of primary pollutants responsible for photochemical smog are:

  • NOx (Oxides of nitrogen)
  • Volatile organic compounds(VOC)
  • CO( Carbon monoxide)

The secondary pollutants are:

  • Ozone(O3)
  • Nitrogen dioxide(NO2)
  • Hydrogen peroxide(H2O2)
  • Peroxyacetyl nitrate(PAN)

These are the equations in the formation of photochemical smog:[2]

NO2 (in presence if sunlight)    NO + O.

O + O2    O3

O3 + hydrocarbons      aldehydes

Hydrocarbons + O2 + NO2    lachrymatory substances (like PAN)

 

Pollution form a coal power station        

        Coal-fired power stations are major sources of pollution. The extensive use of coal is because there is a lot of it around. Although it produces pollutants coal is an important fuel for some considerable time to come.  A coal-fired power station has three main inputs: coal, cooling water pure water to use in steam turbines. The main outputs are electricity, waste heat, CO2, SOx, NOx and ash.

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SOx  emissions

All living organisms contain compounds of sulphur which are the origin of the sulphur found in coal. When coal burns, the sulphur compounds are converted to oxides of sulphur.

NOx Emissions

The flue gases in the power station contain oxides of nitrogen (NOx). This is because fuels contain compounds of nitrogen formed from the proteins contained in organisms. When the fuel is burnt, these nitrogen compounds are oxidised to form fuel NOx .At the high temperature of combustion, atmospheric nitrogen and oxygen combine to form thermal  NOx .

Favourable conditions for photochemical smog ...

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