Measurements of odd nitrogen compounds in the stratosphere by the ATMOS experiment on Spacelab 3

Abstract

The Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment, launched April 30, 1985, on Spacelab 3, measured vertical profiles at 30°N and 48°S of a host of reservoir gases, source 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 NO y family (i.e., NO, NO 2 , HNO 3 , N 2 O 5 , HNO 4 , and ClONO 2 ), thereby giving a direct measurement of the total odd nitrogen mixing ratio for the first time. Some of these species (N 2 O 5 , HNO 4 , ClONO 2 ) 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 [NO], 8.6±1.3 ppbv for [NO 2 ], 7.7±2.1 ppbv for [HNO 3 ], 1.6±0.8 ppbv for [N 2 O 5 ], 0.35±0.14 ppbv for HNO 4 , and 1.4±0.7 ppbv for [ClONO 2 ]. All of these peak values were found in northern hemisphere profiles, with the exception of HNO 3 and the implied value for N 2 O 5 . 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 the key role [NO y ] plays in buffering the odd chlorine depletion effect on ozone. The abundances of 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 [NO y ] measurements, comparisons in this case were made with a lower‐limit profile obtained from the sum of measured nighttime [NO 2 + HNO 3 ] and derived N 2 O 5 , obtained 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 [NO 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.