So, smog which is produced chemically is actually a kind of air pollution.
This poisonous smog is actually produced by the photochemical reaction.
And this photochemical reaction takes place in sunlight, when the Nitrogen oxides and the other volatile organic compound will react in the presence of sunlight then it will lead to the creation of the photochemical smog which is actually a brown haze.
So, smog is made out of Ozone, Nitrogen, smoke, Oxides of Sulfur etc. and so is actually a combination of smoke and fog.
Hence, would obviously be hazardous to the health.
Therefore, Smog is a combination of smoke and fog.