Gas measurements on Western Pacific in Mirai MR01-K02 cruise

The Japanese investigation ship, Mirai, cruised in the Western Pacific in May 2001. The cruise is a part of ACE-ASIA project. During the cruise, we measured atmospheric gas components on the ship. CO, O₃, NO, NO_x, SO₂ were measured continuously by commercial instruments, and 40 canisters were sampled for hydrocarbon measurements and were analyzed by GC-FID and GC-MS in the laboratory in Tokyo. Since the shipped area is located in the east of Japan main island, most of the air masses would be affected by the pollutants emitted in Japan. In May, the wind is mostly coming from the west, and long range transport of polluted air and aerosol would be observed. After leaving the port near Tokyo, the concentrations of CO, O₃, SO₂, NO and NO_x decreased gradually as expected. NO and NO_x are sensitive to the influence of the exhaust emitted from the ship itself. SO₂ is also sensitive to the exhaust from the ship, but there are some small, and broad peaks which are not corresponding to the NO and NO_x peaks. The concentration of O₃ and hydrocarbons decreased drastically after the front passage. Westerly wind polluted in Japan was dominant in most case, but the clean maritime air came from east or south when low pressure passed. The backward trajectories explain the concentration changes of hydrocarbons well. When the air came quickly from Japan, high concentrations were observed. There are good correlation between O₃ and hydrocarbons.