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Air pollution is defined as the presence of one or more undesired airborne contaminants (air pollutants) in the outdoor atmosphere in quantities and duration that can be harmful to the health and welfare of human beings, animal life, plant or property. Air pollutants can be classified into two groups: Primary pollutants and Secondary pollutants. Primary air pollutants are pollutants in the atmosphere that exist in the same form as in source emissions. Examples include carbon monoxide, carbon dioxide, sulfur dioxide, nitrogen oxide, CFCs and particulates. Secondary air pollutants are pollutants formed in the atmosphere as a result of reactions such as hydrolysis, oxidation and photochemical oxidation. Examples include nitrogen dioxides, acidic mists, ozone, and photochemical smog.
Primary and secondary pollutants Air pollution is now a serious problem in many major cities, especially mega cities such as Los Angeles, Tokyo, Mexico city, Beijing, and Hong Kong. One of the most easily perceived problems of air pollution is visibility degradation. Other major effects include greenhouse effect, acid rain and ozone layer depletion. In Hong Kong, air pollution is monitored
by the Environmental Protection Department (EPD). Its work includes
enforcing Air Pollution Control Ordinance, establishing Air Quality
Objectives, operating Air Quality Monitoring Stations and publishing
Air Pollution Index etc. In 1989, the Ozone Layer Protection Ordinance
was enacted to help protect the earth's ozone layer. Recently, the Air
Pollution Programme introduced in 2000 has brought immediate and positive
results in reducing air pollution from vehicles.
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