Abstract
In Japan, the sulfur content in light oil has been reduced two times during this decade by governmental regulation, and the decrease of sulfur dioxide (SO2) level in the ambient air has been often observed throughout Japan. In the air monitoring data for SO2 during 1990-1999 in Nagoya City, the annual mean concentrations had gradually decreased and were found to have very good correlation with the estimated emission amount of SO2. The gross spatial dilution volume (Vd-t) covered the whole area of Nagoya urban area was practically calculated from the correlation to be 0.48×106 km3/(326 km2· year), and the spatial dilution volume (Vd) for the unit area to be 4.03 km3/(km2·day). In addition, Vd-t and Vd for Aichiprefecture, surrounding Nagoya area, were estimated for the comparison. From the published data on SO2 and NOR, Vd-t and Vd for other cities or regions were also calculated. The values of Vd from this and previous studies lie in the range of the 4 times and would be effected by the objective area. The relative higher Vd value would be given in the smaller area because of easy dilution by the airflow around the area. Thus, Vd can be utilized as a coefficient and an index for the estimate of the ambient concentration or the emission amount, or for the dynamics of various pollutants in the air in a certain urban area.
