NARRATOR: This brownish haze, photochemical smog hanging over Los Angeles, results from a combination of factors: the city's plentiful sunshine, high density of automobile traffic, and frequent temperature inversions that trap polluted air.

Photochemical smog tends to occur more often on dry summer days when the region experiences the most sunlight. It is characteristic of urban areas and is thus commonly found in densely populated cities such as Los Angeles, Sydney, Mexico, New Delhi, and Beijing, among many others. It is also sometimes referred to as ‘Los Angeles Smog.’

Secondary pollutants, such as ozone, are formed when primary pollutants undergo chemical reactions in the atmosphere. Photochemical smog, as found for example in Los Angeles, is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes.

It is formed due to photochemical reaction (presence of sunlight) taking place when air contains NO2 and hydrocarbons forming toxic chemicals like peroxyacylnitrates (PAN), Ozone etc.. Los Angeles smog is also known as Photochemical smog. It is reducing* in character. Chemically it is reducing mixture and hence is called reducing smog.

Photochemical smog, which is also known as “Los Angeles smog,” occurs most prominently in urban areas that have large numbers of automobiles. It requires neither smoke nor fog. This type of smog has its origin in the nitrogen oxides and hydrocarbon vapours emitted by automobiles… role of nitric oxide