The Engineer's Joint Council in ‘Air Pollution and Control’ in the U.S. defines air pollution as ‘the existence of one or more types of pollutants, such as dust, smoke, gas haze, offensive odor, smoke, and contamination, sufficient to cause harm to, or disturb, our lives and the lives of plants and animals.’

According to the resources of the World Bank, the level of pollution caused by floating dust, sulfurous acid gas, and nitrogen oxide is represented in the graph below. For Korea, the results shown are based on 1999 records. In accordance with these findings, it is highly possible that the level of pollution has decreased somewhat in other cities as well. Beijing (Peking), Mexico City, Bangkok, and Moscow recorded the highest levels of the three environmental pollutants.

In Korea, the level of dioxide nitrogen has exceeded the recommended level of various international health organizations. Other major cities around the world, such as Tokyo, Paris, L.A., Sydney, Barcelona, Vienna, and New York also have exceeded the recommended levels of these pollutants.