The variation with altitude of the infrared solar spectrum in the 4.5-µm region was observed with a balloon-borne spectrometer. Line-by-line—layer-by-layer analysis of the N<sub>2</sub>O absorption lines in this region yields a detailed N<sub>2</sub>O mixing-ratio altitude profile up to ~20 km. The results show a nearly constant mixing ratio of ~0.33 ppm from 3 to 12 km followed by a gradual decrease to ~0.15 ppm near 19 km. The mixing ratio is estimated to be <0.01 ppm above 20 km.
A. Goldman, D. G. Murcray, F. H. Murcray, and W. J. Williams, "Balloon-borne infrared measurements of the vertical distribution of N2O in the atmosphere," J. Opt. Soc. Am. 63, 843-846 (1973)