The Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment, launced April 30, 1985, on Spacelab 3, measured vertical profile at 30 ¿N and 48 ¿S of a host of reservoir gases, sources gases, and other trace molecules important in the odd nitrogen, odd chlorine, and odd hydrogen chemical families of the middle atmosphere. The measurements included simultaneous observations of all the main elements of the NOy family (i.e., NO, NO2, HNO3, N2O5, HNO4, and ClONO2), thereby giving a direct measurement of the total odd nitrogen mixing ratio for the first time. Some of these species (N2O5, HNO4, ClONO2) represent first detections in the stratosphere, or confirmation of previously published tentative indentifications, and detailed discussion of each is not given here.

The largest mixing ratios observed were ≈13¿2.6 parts per billion by volume (ppbv) for , 8.6¿1.3 ppbv for 2>, 7.7¿2.1 ppbv for 3>. 1.6¿0.8 ppbv for 2O5>, 0.35¿0.14 ppbv for HNO4, and 1.4¿0.7 ppbv for 2>. All of these peak values were found in northern hemisphere profiles, with the exception of HNO3 and the implied value for N2O5. The maximum total odd nitrogen mixing ratio of ≈17¿2.6 ppbv occurred at 43 km (≈2 mbar) and 30 ¿N. These results have important implications because of key role y> plays in buffering the odd chlorine depletion effect on ozone. The abundances of the individual gases and total odd nitrogen levels measured by ATMOS have been compared with prior results obtained from balloon and satellite platforms. Since there are no prior y> measurements, comparisons in this case were made with a lower-limit profile obtained from the sum of measured nighttime 2+HNO3> and derived N2O5, obained from model calculations initialized using earlier satellite results. The lower-limit profile agrees with ATMOS data to within 16% up to 42 km altitude.

Two-dimensional model calculations of y> are as much as 40% larger than ATMOS values above 30 km and up to 40% less than the observations in the lower stratosphere. ¿ American Geophysical Union 1988