The word smog is combination of smoke and fog. At least two distinct types of smog are recognized: Classical smog and photochemical smog.
Classical  smog is also known as sulfurous smog or London smog. Sulfurous smog, which results from a high concentration of sulfur oxides in the air and is caused by the use of sulfur-bearing fossil fuels, particularly coal.
Photochemical smog: This type of smog was observed in Los Angeles(1940s) and hence named as Los Angeles smog. It is formed when the air contains  NO2 and hydrocarbons and the mixture is exposed to sunlight. As the reaction take place in the presence of light to form the smog, it is called photochemical smog.
London Smog and Los Angeles Smog (Classical Smog vs Photochemical Smog)
London Smog vs Los Angeles Smog (Main constituents and chemistry)
Classical Smog vs Photochemical Smog
London smog
Classical smog
Los Angeles smog 
Photochemical smog
This type of smog is first observed in 1952 in London.
This type of smog was first observed  in 1943 in Los Angeles.
It involves smoke and fog (smog)
The word smog is misnomer here as it does not involve any smoke or fog.
It is formed due to presence of SO2 and humidity in the air which combine to form H2SO4 (Sulphuric acid) fog which deposits on the particulates. Therefore London smog  is also known as Sulfurous smog
It is formed due to photochemical reaction (presence of sunlight) taking place when air contains NO2 and hydrocarbons forming toxic chemicals like peroxyacylnitrates (PAN), Ozone etc.. 
Los Angeles smog is also known as Photochemical smog.
It is reducing* in character. Chemically it is reducing mixture  and hence is called reducing smog.
It is oxidizing* in character. It has high concentration of oxidizing agents hence it is known as oxidizing smog.
It causes bronchitis irritation, i.e., problem in the lungs.
It causes irritation in the eyes.
It is formed in the months of winter particularly in the morning hours when temperature is low.
It is formed in the months of summer during afternoon when there is bright sunlight so that photochemical reactions can take place.
*Reduction: in simple terms addition of hydrogen
*Oxidation: addition of oxygen


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  1. amazingly differenced truly helpful thanks..

  2. very good attempt....thanks...

  3. Thanks very helpful! I found nothing about this in Ukrainian so i just translated..


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