LONG-RANGE TRANSPORT OF OZONE, CARBON-MONOXIDE, AND ACIDIC TRACE GASES AT OKI ISLAND, JAPAN, DURING PEM-WEST-B PEACAMPOT-B CAMPAIGN

Ground based measurements of ozone, CO, HNO3, SO2, HCl, and formic aci d were carried out at Oki, a remote island site in the Sea of Japan, d uring February 26 to March 16, 1994, as the Pacific Exploratory Missio n in the Western Pacific/Perturbation by East Asian Continental Air Ma ss to the Pacific Oceanic Troposphere (PEM-West B/PEACAMPOT B) campaig n. According to trajectory analysis, the air mass reaching Oki was cla ssified into four groups: northerly, northwesterly, west-northwesterly , and westerly flows. Clear dependence of gas concentrations on now di rection of air mass was found for all species studied. Lowest concentr ations were observed in the northerly airflow originating from the Ber ing Sea. The mean concentrations of ozone and CO in northerly flow wer e 37.6+/-1.9 and 157+/-7 ppbv, respectively. The mean values of HNO3, SO2, HCl, and formic acid in the northerly now were 34+/-10, 41+/-5, 1 07+/-23, and 54+/-81 pptv, respectively. The highest concentrations of all species were observed in the westerly now passing through a lower boundary layer over the Yellow Sea and South Korean Peninsula. The me an concentrations of ozone and CO in the westerly flow were 45.9+/-4.0 and 292+/-44 ppbv, respectively. The mean values of HNO3, SO2, HCl, a nd formic acid in the westerly now were 137+/-37, 2075+/-1307, 515+/-2 14, and 264+/-183 pptv, respectively. Clear seasonal variation of the ''background'' concentrations of ozone and CO were identified by compa rison with the data from the PEM-West A/PEACAMPOT A campaign conducted in the fall. In contrast to other species, strong diurnal variation o f formic acid with a daytime maximum was observed. The possibility of photochemical formation of formic acid from HCHO and the HO2 radical i s discussed.