Vertical distributions of N<sub>2</sub>O isotopocules in the equatorial stratosphere

Abstract. Vertical profiles of nitrous oxide (N2O) and its isotopocules, isotopically substituted molecules, were obtained over the equator at altitudes of 16–30 km. Whole air samples were collected using newly developed balloon-borne compact cryogenic samplers over the Eastern Equatorial Pacific in 2012 and Biak Island, Indonesia in 2015. They were examined in the laboratory using gas chromatography and mass spectrometry. The mixing ratio and isotopocule ratios of N2O in the equatorial stratosphere showed a weaker vertical gradient than the previously reported profiles in the subtropical and mid-latitude and high-latitude stratosphere. From the relation between the mixing ratio and isotopocule ratios, further distinct characteristics were found over the equator: (1) Observed isotopocule enrichment factors (ϵ values) in the middle stratosphere (25–30 km) are almost equal to ϵ values reported from broadband photolysis experiments conducted in the laboratory. (2) ϵ values in the lower stratosphere (