What is smog? How is classical smog different from photochemical smog?

(N/A) The word smog is derived from smoke and fog. This is the most common example of air pollution that occurs in many cities throughout the world. There are two types of smog:
$(i)$ Classical smog: This type of smog occurs in cool,humid climates. It is a mixture of smoke,fog,and sulphur dioxide $(SO_2)$. It is also called reducing smog because it is a chemically reducing mixture.
$(ii)$ Photochemical smog: This type of smog occurs in warm,dry,and sunny climates. It is produced due to the action of sunlight on unsaturated hydrocarbons and nitrogen dioxide $(NO_2)$ produced by automobiles and factories. It is also called oxidising smog because it has a high concentration of oxidising agents.