Surface ozone and carbon monoxide levels observed at Oki, Japan: Regional air pollution trends in East Asia

Simultaneous ground-based measurements of ozone and carbon monoxide were performed at Oki, Japan, from January 2001 to September 2002 in order to investigate the O3 and CO characteristics and their distributions. The observations revealed that O3 and CO concentrations were maximum in springtime and minimum in the summer. The monthly averaged concentrations of O3 and CO were 60 and 234 ppb in spring and 23 and 106 ppb in summer, respectively. Based on direction, 5-day isentropic backward trajectory analysis was carried out to determine the transport path of air masses, preceding their arrival at Oki. Comparison between classified results from present work and results from the year 1994-1996 was carried out. The O3 and CO concentration results of classified air masses in our analysis show similar concentration trends to previous findings; highest in the WNW/W, lowest in N/NE and medium levels in NW. Moreover, O3 levels are higher and CO levels are lower in the present study in all categories.