LOWER TROPOSPHERIC OZONE TREND OBSERVED IN 1989-1997 AT OKINAWA, JAPAN

In order to elucidate recent tropospheric ozone trends in Northeast As ia, 8 year-long ozone sounding data obtained between 1989 and 1997 at Naha (Okinawa Island), Japan, were analyzed incorporating with backwar d trajectory categorization. Focusing on the regionally polluted conti nental outflow, only data associated with air masses that reached Naha from northern, northwestern, and western directions during autumn/ wi nter/early spring seasons (from October to March) were selected for an alysis. The concentration of ozone shows an increase of about 2.5 +/- 0.6 % (one standard deviation) per year for a 0 - 2 km layer from the ground representing the planetary boundary. The surface ozone concentr ations obtained at Cape Hedo (northern tip of Okinawa Island) at the s ame timing as the selected ozone sounding also showed an increasing tr end of 2.6% per year but with a large statistical uncertainty of + 2.0 %. This result is in accordance with the 22-year period (1969-1990) o f tropospheric ozone trends, 1.5 - 2.5 % per year, obtained previously at three other Japanese ozone sounding stations, Kagoshima, Tsukuba, and Sapporo [Akimoto et al. 1994], demonstrating the continuous increa se of tropospheric ozone in Northeast Asia in 1990s. It is suggested t hat this tropospheric ozone trend would be related to the increasing e mission of NOx from Northeast Asian region (China, Japan, South Korea, Taiwan) during this period with a rate of 3.9% per year.