LONG-RANGE TRANSPORT OF OZONE IN THE EAST-ASIAN PACIFIC RIM REGION

Measurements of surface ozone were conducted at three remote island si tes in the East Asian Pacific rim region during the Pacific Explorator y Mission-West (A) campaign period in September-October, 1991. The ozo ne concentrations observed at the three measurement stations at Oki an d Okinawa, Japan, and Kenting, Taiwan, had similar ranges varying betw een 6-63, 8-58, and 4-65 ppb, respectively, except for one event of sh ort-range transport of polluted air at Kenting, Day-to-day variations have been analyzed by using backward air parcel trajectories on isentr opic surfaces, The results showed that continental air masses which or iginated from northwestern Asia and passed through the high anthropoge nic emission region of East Asia contained the highest concentration o f ozone, 30-60 ppb with an average of 43-45 ppb at the three stations. In contrast, the lowest concentrations were observed for air parcels originating from the mid-Pacific and transported without mixing with t he continental outflow. These parcels contained 5-20 ppb of ozone with the average of 11, 15, and 9 ppb at Oki, Okinawa, and Kenting, respec tively, The air parcels from the South China Sea contained 22 and 18 p pb of ozone at Okinawa and Kenting, respectively, which were higher th an those from mid-Pacific. Continental air mass from the north-northea st to Oki containing 35-40 ppb ozone with the average of 37 ppb was re cognized as continental ''background.'' The high ozone concentrations in the northwesterly continental outflow exceeding the background was ascribed to photochemical buildup in the planetary boundary layer.