Trends of air quality and atmospheric deposition in Tokyo

The trends of air quality and atmospheric deposition in the past 20 or more years in Tokyo are summarized. In the late 1960s and early 1970s the levels of SO2, SO42−, airborne particulate matter and its elemental compositions were high but their levels have rapidly declined until the 1970s because of their emission control and fuel and material switching. Recently, however, the decline has slowed down. The number of days on which Mt. Fuji was visible from Tokyo have increased in coincidence with the decrease of particulate matter concentration. The decrease of deposition of SO42− and other species also reflects the decline of air pollutant concentration. However, the atmospheric concentration and deposition of oxides of nitrogen did not decrease because of the increase of number of automobiles. It is also recognized that the alteration of structure of the city changes air quality.