A STUDY OF THE REACTION NAO2-]NAO+O2 - IMPLICATIONS FOR THE CHEMISTRYOF SODIUM IN THE UPPER-ATMOSPHERE(O)

Sodium superoxide (NaO2) is believed to be a major sink for meteor-abl ated Na in the upper atmosphere. However, the rate constant for the re action between NaO2 and O is not known, and its determination is the s ubject of this study. NaO2 was produced by the reaction between Na vap or, an excess of 02, and the carrier gas N2 in the upstream section of a fast flow tube reactor. Excess atomic 0 was then added, so that a s teady state developed in which the sodium was partitioned between its atomic form and a variety of oxides. The steady state fraction of atom ic Na, monitored by laser-induced fluorescence, was then observed as a function of [0] and [O2], from which it was deduced that k(NaO2 + O) = (2.2 +/- 1.0) x 10(-11) cm3 molecule-1 s-1 at 300 K (3sigma uncertai nty). As a prelude to this experiment, the recombination reaction betw een O2 and Na was studied by the conventional flow tube technique, yie lding k(Na + O2 + N2) = (3.14 +/- 0.20) x 10(-30) (300/T)-(1.52 +/- 0. 27) cm6 molecule-2 s-1. These experimental results were then incorpora ted into a one-dimensional model of sodium in the upper atmosphere bet ween 65 and 110 km. It is shown that formation of NaHCO3 rather than N aO2 is the dominant removal process for atomic Na below 90 km. This ne w model, whose only important assumption is the rate constant for the reaction NaHCO3 + H --- > Na + H2CO3, predicts a seasonal variation of the atomic Na layer in excellent agreement with recent lidar observat ions at 40-degrees and 69-degrees-N and also demonstrates that tempera ture fluctuations produced by gravity waves should induce significant chemical responses in the Na layer below 88 km.