Influence of regional-scale anthropogenic activity in northeast Asia on seasonal variations of surface ozone and carbon monoxide observed at Oki, Japan

Surface O-3 and CO measurements were carried out at Oki, Japan during March 1994 to February 1996 in order to elucidate the processes determining temp oral variations of O-3 and CO in the northeast Asian Pacific rim region. Th e isentropic trajectory analysis was applied to sort out the influences of the air mass exchange under the Asian monsoon system and the regional-scale photochemical buildup of O-3. The trajectories were categorized into five groups which cover background and regionally polluted air masses. The seaso nal cycles of O-3 and CO in the background continental air mass revealed sp ring maximum-summer minimum with averaged concentrations ranging from 32 an d 120 ppb to 45 and 208 ppb, respectively. In contrast,, O-3 concentrations in the regionally polluted continental air mass ranged from 44 to 57 ppb a nd showed a winter minimum and a spring-summer-autumn broad maximum, which was characterized by photochemical O-3 production due to anthropogenic acti vities in northeast Asia. CO concentrations in the same air mass showed a s pring maximum of 271 ppb and a summer-autumn minimum of 180 ppb. The photoc hemical buildup of O-3 resulting from anthropogenic activities in this regi on was estimated to be 21 ppb in summer, while its production was insignifi cant, an average 3 ppb, in winter. A comparison between data in northeast A sia and in Europe shows many similarities, supporting the contention that p hotochemical buildup of O-3 from large-scale precursor emissions in both re gions is very significant.