Photochemical smog and industrial smog
A combination of primary pollutants such as carbon monoxide, nitric oxide and hydrocarbons ans secondary pollutants such as nitrogen dioxide, nitric acid, ozone, hydrogen peroxide, peroxacyl nitrites (P.A.N.s) and formaldehyde, produced and some of the primary pollutants interact under the influence of sunlight.
Breathing and respiratory problems in human-beings and reduces visibility leading to accidents
Moreover, cities in which photochemical smog predominates usually have sunny warm and dry climate. For example- photochemical smog occurs during the early morning traffic rush hours. It causes breathing and respiratory problems in human-beings and reduces visibility leading to accidents.
It consists of a mixture of sulfur dioxide and S.P.M including a variety of solid particles and droplets of sulfuric acid formed from some of the sulfur dioxide. This type of air pollution tends to predominate during the winter (especially in the early morning) in heavily industrialized urban cities. It causes toxic effects on plants, animals and human beings.
Vehicular pollution is due to the failure of transport management in these cities
The main of methane are gas leaks from coal mines, biomass burning and garbage, landfills, enteritis fermentation in cattle and insects etc.
WHO has issued global air quality guidelines which set voluntary targets for particulate matter pollution. Urban air quality has deteriorated in all pollution has reached intolerable levels. This reflects a combination of vehicular and industrial emissions. Further vehicular pollution is due to the failure of transport management in these cities.