In the production of photochemical smog, there are primary and secondary sources that contribute to its production.

Authors Avatar

In the production of photochemical smog, there are primary and secondary sources that contribute to its production. Primary sources are injected directly into the atmosphere, whereas secondary sources are formed in the atmosphere through chemical and photochemical reactions. As the graph shows, motor vehicles (the red and pink columns) contribute largely to most of the primary pollutants. The main pollutants though are Carbon Monoxide and oxides of nitrogen (Nox). Motor vehicles also contribute largely to the secondary pollutant Nitrogen Dioxide.

During the combustion of coal, primary pollutants are formed. Oxides of Nitrogen and Sulphur are formed because is there is both nitrogen and sulphur in coal – initially from the decomposed organisms. This becomes oxidised by burning. Oxides of Nitrogen are also created because there is such a high temperature of combustion, atmospheric nitrogen and oxygen form what is called thermal NOx (1).

Photochemical smog is a condition that develops when primary pollutants interact under the influence of sunlight (2) to produce secondary pollutants.

Several reactions lead to the production of the constituents of photochemical smog, taking place in the troposphere. Ozone is present in all levels of the atmosphere, even in unpolluted air.  In unpolluted air, Nitrous Oxide reacts with the ozone, producing Nitrous Dioxide and Oxygen:

Join now!

                03 + NO                 NO2 + O2                (a)

However, natural sunlight breaks down the Nitrous Dioxide when the wavelength is less than 435nm:                NO2 + sunlight                NO + O                (b)

This atomic oxygen (from (a)) then reacts with the abundant oxygen (from (b)) to form ozone:

                O2 + O                O3                        (c)

The ozone created and broken down soon reaches a steady equilibrium. However if this air becomes polluted with hydrocarbons and oxides of nitrogen, ozone levels increase. This is because Nitrogen oxide can become Nitrogen Dioxide without destroying Ozone. To demonstrate this let us represent the hydrocarbon with RCH3:                

                RCH3 + OH                RCH2 + H20        (d)

                RCH2 + O2                  RCH2O2                (e)

The peroxy radical ...

This is a preview of the whole essay