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.