The correct answer is “Ozone”.
The photochemical smog always contains the Ozone gas or O3 as a pollutant.
Photochemical smog is a type of smog that is produced when UV light originating from the sun interacts with the oxides of nitrogen present in the atmosphere.
This type of smog usually manifests as a brown haze and is most commonly seen in highly populated cities that are placed in relatively warm climates.