3. ESTIMATION OF EMISSION INTENSITY DISTRIBUTION WITHIN TOKYO BAY
Fuel consumption necessary for operation of ships in a certain limited sea area can be estimated from the data such as the number of sailing ships, operating modes, load factor and the specific fuel consumption during each mode of operation of various ships. Fig.4 shows a map of pollution intensity along routes of ships within Tokyo Bay.
Then the intensity of SOx or NOx emissions can be calculated by multiplying fuel consumption by the aforementioned emission data. Figs. 5 and 6 show the distribution of emission intensity of SOx and NOx, respectively. It can be seen that the emission intensity is bigger in harbors such as Yokohama, Kawasaki, Tokyo, Chiba, Yokosuka and Kisarazu compared with that at the center part of the bay. The total number of ships which entered these harbors in 1994 was 312,992 which represents around 10% of the total number of ships entered harbors in Japan in this year. By gross tonnage, relatively small-sized ships of less than 500 gross tons (tankers or bulk carriers) are almost 2/3 of the total. This is the common feature of domestic marine transport in Japan. Many of these small-sized tankers use main engines as power sources at the time of cargo handling operations. This fact yields peak values at Yokohama sea berth and others. Since cargo ships other than oil tankers use power sources on land in many cases, fuel consumption of ships becomes relatively smaller and the emission intensity also reduces. The total amount of SOx emission in Tokyo Bay is 19,700 t/y in 1994, in which 11,200 t/y during mooring, and almost 1/4 is from domestic small ships. For NOx, 30,800 t/y is the grand total, and 19,500 t/y is during mooring, and around 1/5 is from smaller ships. Incidentally, the total amount of NOx emissions from automobiles in the whole area of Tokyo was 17,500 t/y for passenger cars, 34,700 t/y for trucks, and the grand total was 52,200 t/y in 1990. Then the NOx emission from ships should not be ignored in Tokyo area. These estimation have been performed by MAP Committee in '93 and '94, but S&O Committee also obtained similar results independently, by adopting similar procedures in 1993.
4. TURBULENT DIFFUSION ANALYSIS AND ESTIMATION OF POLLUTANT DENSITY ON LAND
Based on these emission intensity distribution, the turbulent diffusion analysis of the pollutants within the atmosphere has been performed. The turbulent diffusion characteristics should be considerably different from that on land. A simulation model for the analysis of turbulent atmospheric boundary layer based on modified OCD/APT model [3] developed by D. Godden & S.R. Hanna has been developed by MAP Committee. Calculations have been carried out by using the data of velocity and direction of wind, temperature of air and of sea water, taken hourly and accumulated through a year around the Tokyo Bay. Also the turbulent diffusivity over the sea and on land is estimated by taking into account the instability of atmosphere. This model agreed well with the measured data taken by using a laser rader.
Calculated results are shown in Fig.7. It can be seen that both the values of SOx and NOx concentration are high around the harbors. There are many monitoring stations on land around the coastal area of Tokyo Bay distributed by the Environment Agency of the Government of Japan, as shown in Fig.8, which are measuring and recording SOx and NOx concentration in the atmosphere continuously through out of the year. Fig.9 shows the SOx and NOx concentration within atmosphere and its contribution percentage to the overall density at the monitoring stations designated in Fig.8. In the case of SOx, there is a point at where the yearly averaged contribution percentage of ships reaches as high as 50%.
Fig.4. Estimation of Sources of Emission in Tokyo Bay
Fig.5. SOx Emission Intensity Distribution in Tokyo Bay
Fig.6. NOx Emission Intensity Distribution in Tokyo Bay
