Smog can be classified into two main types based on their climate conditions and chemical composition. Classical smog occurs in cool, humid climates and is characterized by a mixture of smoke, fog, and sulfur dioxide. It is also known as reducing smog. Photochemical smog, on the other hand, occurs in warm, dry, and sunny climates and results from the action of sunlight on unsaturated hydrocarbons and nitrogen oxides produced by automobiles and factories. It has a high concentration of oxidizing agents and is called oxidizing smog.