Tokyo's effort to clean up its environment was of a more recent nature - the last three decades, to be more precise. Tokyo today is a recognised example of how air quality in an industrial city can be drastically improved. Despite the limitations placed on them, the cities of both Los Angeles and Tokyo have shown the way especially when it comes to the areas of air quality control. Traditionally, the most common air pollutants in the urban environment are carbon monoxide, sulphur dioxide, nitrogen oxides, ozone, suspended particulate matter and lead. Industrial pollution refers largely to fossil fuels that are burnt in stationary sources leading to production of sulphur dioxides, nitrogen oxides and suspended particulate matter.
Domestic pollution is also responsible for producing the above air pollutants.
Petrol-fuelled vehicles are primarily sources of unburnt hydrocarbons, carbon monoxides and lead. Diesel vehicles, on the other hand are sources of nitrogen oxides and significant quantities of suspended particulate matter. While it is concluded that motor vehicles are the primary source of urban air pollution in developed countries, the case is different in developing countries. The reason is that developing countries trace their air pollution problems to industrial, domestic and vehicular sources. Bringing this source-context into a home scenario, it follows then that the air pollution problem in India can broadly be traced to these three sources.