Previous Year Question
Photo chemical smog always contains
Aluminium ion
Ozone
Methane
Phosphorus
Correct Answer: B
Detailed Solution
Photochemical Smog is primarily an oxidising smog that develops under warm, dry and sunny conditions. It is formed particularly through photochemical reactions involving Nitrogen Oxides (NOₓ) and Volatile Organic Compounds (VOCs) released from vehicles and other combustion sources.
During these reactions, Ozone (O₃) is formed as an important secondary pollutant. Therefore, ground-level Ozone is a major characteristic component of photochemical smog.
The process can be understood simply as:
NOₓ + VOCs + Sunlight → Photochemical reactions → O₃ and other secondary pollutants
Besides Ozone, photochemical smog may contain PAN (Peroxyacetyl Nitrate), Aldehydes, Nitrogen Dioxide and other photochemical oxidants.
It is important to distinguish Stratospheric Ozone from Tropospheric Ozone. Stratospheric Ozone protects Earth from harmful UV radiation, whereas ground-level/Tropospheric Ozone is a harmful air pollutant and an important component of photochemical smog.
Methane is a Greenhouse Gas but is not the defining compulsory component intended in this question. Aluminium ion and Phosphorus are also not normal components of photochemical smog.