3. RATIO OF ATMOSPHERIC POLLUTANTS CONTRIBUTED BY SHIPS
Atmospheric emissions from ships was calculated by multiplying the amount of fuel consumed by the factors for the various emissions from each ship. These amounts are compared to land-based amounts in figure 4 and 5. Figure 4 shows that for waters surrounding Japan, NOx had the heaviest concentration, at 37%, SOx was next at 23%, while CO2, in almost direct proportion to fuel used, decreased to 3%.
In comparison with CO2, which is emitted in almost direct proportion to the amount of fuel used, the high contributions of NOx and SOx is, as mentioned earlier, attributable to the fact that although regulations concerning these two substances are increasingly stringent for land-based emissions, no such regulations exist for marine engines, fuel of poor quality is often used, and engine efficiency is given first priority.
In regard to incompletely combusted substances that are emitted, such as CO and CH4, combustion conditions being generally better for ship engines than for automobiles, and the low fuel amounts consumed during transit, the emissions factors are estimated to be small, and the contribution to overall emissions to be at the same level as CO2, or in direct proportion to amounts of fuel consumed.
In looking at global emissions, compared to the 2% that CO2 occupies, NOx at 13% and SOx at 6% are disproportionately high, reflecting a lack of forethought in regard to ship engine emissions compared to their counterparts on land.
Emission from ships around Japan includes emission from ships for internal navigation, Fishery boats. Pleasure boats and the ships engaged in the international navigation when they port in Japan and sail the sea in 200 nautical miles from Japan
Unit; 103t (except contributory rate)
Land-based sources include mobile sources except ships, stationary sources, industrial processes, etc.
Fig.4 Emissions from ship around Japan and comparison with total emissions in Japan
NOx and SOx are referred to in the 1996 data by Oliver J.G.J, et al (1996) Description of EDGER Version 2.0: a set of global emission inventories of greenhouse gases and ozone-depleting substances for all anthropogenic and most natural sources on a per country basis and on 1 deg × 1 deg grid. CO2 amounts are referred to in the 1996 data in BP Statistical Review of World Energy 1997. This includes ships.
Fig.5 The worldwide emissions from ship and comparison with total emissions
4. A DISPERSAL SIMULATION OF ATMOSPHERIC POLLUTANTS FROM SHIPS
In calculations for the dispersal simulation in the region around Japan, data from Tokyo and Osaka bays were used.
In the dispersal calculations for Tokyo bay, it was thought that S02 and NOx concentrations upon reaching the shoreline would possibly increase with a yearly average of 6 ppb and 15 ppb respectively (See Fig.6, 7) [2]. In Osaka bay, during a short-term simulation, while it was thought that S02 and NOx hourly concentrations would possibly increase with 30 ppb and 40 ppb respectively, the O3 concentration was shown not to have a great effect (See Fig.8) [3]. In comparison to the contribution of land based emissions to atmospheric environmental concentrations in inhabited areas, that of ships is smaller due to the distance at which these gases are emitted, allowing them more time for diffusion before reaching the inhabited areas.
However, in regard to NOx, as it is known to be a precursor simulations of dispersal conditions alone are thought to be inadequate and should include a sedimentation process and photochemical reaction process in future.
