SMOG by Emre YAZICIOĞLU 1140 , 12 / C

Smog, is a term coined from the words ‘smoke’ and ‘fog’ arose from the conditions of coal smoke and fog experienced by the city of London in the early part of the 19th century. There are two types smog: Industrial or Reducing Smog Photochemical or Oxidizing Smog

Industrial Smog The reason of industrial smog is; combustion of sulfur containing coal used for heating, manufacturing process in industry and the generation of electricity. That’s why this type of smog mainly found in coal burning cities such as Chicago and Beijing. Industrial smog consists of water droplets, sulfur dioxide and trioxide, soot, ash and sulfuric acid.

Photochemical Smog It is the second type of smog and it is also known as oxidizing smog. It is like a chemical soup containing hundreds of different substance formed in the atmosphere as a result of free radical reactions brought by ultraviolet radiation from the sun. That is the reason why it is called photochemical smog.

Photochemical smog forms in large cities and occurs more in cities which are bowl shaped. Also lack of wind cause to form photochemical smog in large cities. These factors prevent air to move. The warm,dry,cloudless conditions are ideal for the formation of photochemical smog as any ultraviolet light from the sun’s rays is easily able to reach the Earth

The Formation of Photochemical Smog Photochemical smog is formed mainly because of thermal inversion In normal conditions, as the attitude increases the temperature decreases. The warm air in the surface of the earth rises with pollutants and cooler air in the upper part of atmosphere takes place of warm air. The cooler air in the surface of Earth warmed by Earth’s surface and it rises too. This process contiunes regulary.

The main sources of primary pollutants for photochemical smog are: Volatile Organic Chemicals ( VOCs) (act as catalysts) Nitrogen Oxides ( especially NO from automobile exhaust)

The Formation of nitrogen monooxide as a primary pollutant N2 (g) + O2 (g)  2 NO (g) (Needs high temperature!) Nitrogen monooxide oxidized to brown nitrogen dioxide gas either by oxygen of ozone. 2 NO (g) + O2 (g)  2 NO2 (g) or NO (g) + O3 (g)  NO2 (g) + O2 (g)

As the solar radiation is avaible in morning uv light takes place to produce oxygen radical. NO2 (g) + uv light  NO (g) + O (g) Oxygen Free Radical takes place many reactions to form secondary pollutants such as ozone and hdroxyl radicals O (g) + H2O (l)  2 OH (g)

Hydroxyl Radicals takes place these reaction to form nitric acid and radical propagation OH (g) + NO2 (g)  HNO3 (aq) OH (g) + RH (g)  R (g) + H2O (l)

Then peroxide free radical is formed by using last reaction R (g) + O2 (g)  ROO Peroxide radicals react with nitrogen dioxide to form peroxyacylnitrates. ROO + NO2 (g)  ROONO2