Air pollution is caused by many things. Before pointing out the health hazards I'll say what I know of the causes.
The black asphalt that is used in parking lots, driveways, roads and roof tops is a major contributor.
Diesel fumes from trucks and other sources.
Poor emissions from automobiles releasing carbon monoxide into the air.
Urban heat islands that are made up of black asphalt roads, parking lots, etc are slowly being changed around the country and world to a light colored surface. Black holds heat and has poor emission and poor reflectivity allowing the atmosphere to heat up to 65 degrees F warmer than the actual air temperature over a grass surface.
Air pollution causes respiratory ailments such as asthma and lung diseases. It can shorten life in humans and animals.
That is why it is important to plant trees and other greenery so those plants can absorb the carbon dioxide from the air and release oxygen.
During the summer thunderstorms can erupt from out of nowhere so to speak, over large black top areas.
Industry and cities have to bite the bullet and stop using materials that contribute to air pollution. Some cities have laws mandating greening.