Industries were often located in towns and cities, and together with the burning of coal in homes for domestic use, urban air pollution levels often reached devastating levels. During foggy conditions, pollution levels escalated and urban smogs (smoke and fog) were formed. These often brought cities to a halt, disrupting traffic but more dangerously causing death rates to dramatically rise.

The effects of this pollution on buildings and vegetation also became obvious. However, Rapid urbanization, motorization and economic growth contribute to a growing air pollution problem in most large developing urban centers. The number of motor vehicles in urban areas steadily increased and air quality problems associated with motor vehicles became more prevalent.

In the early 1980s, the main interest was the effects of lead pollution on human health, but by the late 1980s and early 1990s, the effects of other motor vehicle pollutants became a major concern. The 1990s have seen the occurrence of Smogs. These are not caused by smoke and sulfur dioxide pollution but by chemical reactions occurring between motor vehicle pollutants (Volatile Organic Compounds (VOCs) and sunlight. These are known as ‘photochemical smogs’.