Answer

It is the chemical reaction of sunlight, Nitrogen oxides and Volatile organic compounds in the atmosphere, which leaves airborne particles and ground level ozone.

Photochemical smog forms from the combustion residues of petrol and diesel engines. This lethal mixture of air pollutants can include the following:

• Aldehydes
• Nitrogen oxides such as Nitrogen Dioxide
• Peroxyacyl Nitrates
• Volatile organic compounds
• Tropospheric Ozone

All of these harsh chemicals are usually highly reactive and oxidizing. Photochemical smog is therefore considered to be a problem of modern industrialization. It is present in all modern cities, but it is more common in cities with sunny, warm, dry climates and a large number of motor vehicles. Because it travels with the wind, it can affect sparsely populated areas as well.