Fog — is a form of cloud on the earth's surface containing tiny water droplets. These water droplets are capable of remaining suspended in the air for hours.
Smog — is a deadly mixture of smoke and fog. The smoke that would otherwise hang higher in the sky and the dust particles that would fall to the ground remain suspended in the air as they mix with the fog and cause a photochemical reaction.
Fog: colorless, odorless, 100% humidity, dew is formed
Smog: has a shade from yellowish to bluish, often has an odor of burning, can be when the air humidity is normal.