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

1. Smog is the type of smoke that has fog in reality.

2. Smog is basically derived from the merging of two words; smoke and fog.

3. Smog is a yellowish or blackish fog formed mainly by a mixture of pollutants in the atmosphere which consists of fine particles and ground-level ozone.

4. Smog which occurs mainly because of air pollution can also be defined as a mixture of various gases with dust and water vapor.

Industrial smog contains two primary components: sulphur dioxide and particulate matter. These combine with the water in the fog to produce acidic precipitation -- sulphur dioxide dissolves in water to form sulfuric acid -- and thick, tar-laden droplets.

The primary pollutant in photochemical smog, on the other hand, is ozone. It is produced when nitrogen oxides and volatile organic compounds in automobile and fossil-fuelled power-plant emissions combine with oxygen in the air in direct sunlight. Whereas industrial smog casts a grey pallor over the areas it affects, the nitrogen dioxide in photochemical smog creates a dingy, brownish haze.