NITRIC-OXIDE IN THE EQUATORIAL PACIFIC BOUNDARY-LAYER - SAGA-3 MEASUREMENTS

As part of the Soviet-American Gases and Aerosols (SAGA) experiment, mixing ratios of atmospheric nitric oxide were measured at the surface of the equatorial Pacific Ocean between Hawaii and American Samoa during February and March 1990. Overall, NO mixing ratios for measurements made between 0800 and 1600 LT averaged 2.9 +/- 0.1 parts per trillion by volume (pptv), where the uncertainties represent 95% confidence limits in the mean. Concentrations were generally highest near the equator: NO mixing ratios obtained between 0800 and 1600 LT averaged 4.0 +/- 0.2 pptv in the 5-degrees-S-5-degrees-N latitude band and 2.1 +/- 0.2 pptv in the 5-degrees-15-degrees bands north and south of the equator. In the equatorial band the average diurnal behavior was a steady rise in NO from early morning until local noon, reaching a peak of about 4.5 pptv that remained until late afternoon before beginning a rapid decline. In the 5-degrees-15-degrees bands north and south of the equator the average diurnal curve for NO was flat (within experimental uncertainties) at about 2 pptv from 0800 to 1600. These findings are consistent with previous measurements of NO in both boundary layer and free tropospheric remote Pacific environments. They confirm a picture of the remote equatorial Pacific boundary layer as a region of low NO and net photochemical destruction Of O3. The NO and O3 measured on SAGA 3 correspond to a loss rate of ozone of approximately 1 parts per billion by volume (ppbv) O3/day in a region where mean surface O3 is 10 ppbv.