REACTIVE NITROGEN OVER THE PACIFIC-OCEAN DURING PEM-WEST-A

Measurements of NO and NOy were carried out during NASA's Pacific Expl oratory Mission-West A. In total, 18 aircraft flights were made over t he Pacific Ocean, predominantly over the western Pacific Ocean in Sept ember and October 1991. NO and NOy were measured using a chemiluminesc ence instrument, and NOx was calculated from NO using a chemical box m odel. The measurements were carried out from 0.3 to 12 km in altitude. The NO, calculated NOx ((NOx)(mc)), and NOy mixing ratios in continen tal air were significantly higher than in maritime air. In maritime ai r, NO increased with altitude. The median values of NO in the boundary layer and the lower, middle; and upper troposphere were 3.7, 5.1, 11. 5, and 26.6 parts per trillion by volume (pptv), respectively. In cont inental air, NO and (NOx)(mc) mixing ratios revealed a C-shaped profil e. The median NO values observed in the four altitude regions were 37. 8, 17.5, 18.2, and 53.2 pptv, respectively. NOy did not show any appar ent altitude dependence either in maritime or in continental air. In m aritime air, median NOy values in the lower, middle, and upper troposp here ranged between 211 and 226 pptv and in continental air between 38 2 and 401 pptv. The lowest values of NOy, PAN, and O-3 were observed i n tropical air masses throughout the entire altitude region. In the mi ddle and upper troposphere of the high-latitude air masses, NO and (NO x)(mc) values were the lowest, although NOy mixing ratios were similar to those in continental air masses. PAN, O-3, CO, CH4, and C2H6 data were used to study the budget of reactive nitrogen over the Pacific Oc ean. O-3 mixing ratios were found to be correlated with those of (NOx) (mc), NOy, PAN, and CH4, although the degree of correlation varied wit h air mass and altitude. These correlations, together with the profile s of these species, suggest that photochemical production of O-3 from precursor species over the continent is important for the O-3 budget i n the troposphere over, the western Pacific Ocean.