Hello ,

Smog can be classified mainly into two types :

1. Classical or Sulphurous Smog : In early hours of winter in the presence of carbon and many other chemicals SO2 changes to SO3 and then H2SO4. This mixture forms the classical smog. 1st observed in London when 4000 people died and hence this smog is also known as London Smog. It is a reducing smog.
2. Photochemical or Loas Angeles Smog : Was 1st observed in 1950 Los Angeles in Summer in presence of Sunlight when NO2 and Hydrocarbons were present in large quantity due to vehicular pollution.The photochemical smog contains Peroxyacetyl nitrate (PAN), Nitrous acid (HNO2) and Nitric acid (HNO3) , Acrolein etc . It is a oxidising smog and has brown haze.