Various aspects of the air quality problems caused by ambient particles in and around the city of Seoul are discussed. First, the trend of the air quality in Seoul over time is investigated along with the types and quantities of energy consumption in Seoul. It was found that the general air quality in Seoul has improved over the last twenty years because of a change in the primary fuel used in Korea. However, the visibility in Seoul, a representation of the ambient particle concentration, is still worse than in other cities in Korea. In the air around Seoul, secondary particle generation might be as important as particles directly emitted from within the city or transported from outside.