MEASUREMENTS OF NO, NOY, CO AND O3 AND ESTIMATION OF THE OZONE PRODUCTION-RATE AT OKI-ISLAND, JAPAN, DURING PEM-WEST

Measurements of NO, NOy, CO, and O-3 Were conducted at Oki Island, 65 ion west of the Japanese mainland during September-October 1991. The r esults show that the Oki Island site is relatively clean with mean (an d median) CO and NOy concentrations of 137 (130) ppbv and 713 (505) pp tv, respectively. These relatively low concentrations reflect the freq uent occurrence of winds from the less populated regions to the north during this campaign. During several periods, elevated CO, NOy, and O- 3 concentrations were associated with transport of pollutants from Jap an and Korea. CO and NOy are significantly correlated in the entire da ta set, reflecting the overall influence of anthropogenic emissions. M ean CO and NOy concentrations show small diurnal cycles with a maximum in the morning and early evening hours. Hourly mean O-3 concentration s exhibit a diurnal cycle of amplitude 3.5 parts per billion by volume , with a maximum in the early afternoon attributed to photochemical O- 3 production. The source of this afternoon O-3 enhancement is analyzed using regression analysis of O-3 and NOy and of O-3 and CO. Both NOy and CO are significantly correlated with O-3 during the daytime but ar e poorly or insignificantly correlated with O-3 at night, indicating t hat upwind photochemistry operating within the previous similar to 1 d ay was responsible for the observed afternoon O-3 enhancement. The NOy -O-3 regression analysis indicates formation of similar to 9 O-3 molec ules per NOy molecule reaching Oki Island. The mean and median midday NO concentrations of 55 and 23 parts per trillion by volume, respectiv ely, were sufficient to support net production of O-3. Using the resul ts of these measurements and prior modeling studies (Lin et al., 1988) , we estimate a ''lifetime-averaged'' O-3 production efficiency of 10 molecules O-3 per NOx molecule. Combined with estimated East Asian NOx emissions for 1987, this indicates an annual O-3 production of 1.0 x 10(14) g O-3 from photochemistry which is approximately 2 times the an nual stratospheric flux in this region. This value must be considered as a rough estimate but is probably accurate to within a factor of 2.