AN INTERCOMPARISON OF AIRCRAFT INSTRUMENTATION FOR TROPOSPHERIC MEASUREMENTS OF CARBONYL SULFIDE, HYDROGEN-SULFIDE, AND CARBON-DISULFIDE

This paper reports results of NASA's Chemical Instrumentation and Test Evaluation (CITE 3) during which airborne measurements for carbonyl s ulfide (COS), hydrogen sulfide (H2S), and carbon disulfide (CS2) were intercompared. Instrumentation included a gas chromatograph using flam e photometric detection (COS, H2S, and CS2), a gas chromatograph using mass spectrometric detection (COS and CS2), a gas chromatograph using fluorination and subsequent SF6 detection via electron capture (COS a nd CS2), and the Natusch technique (H2S). The measurements were made o ver the Atlantic Ocean east of North and South America during flights from NASA's Wallops Flight Center, Virginia, and Natal, Brazil, in Aug ust/September 1989. Most of the intercomparisons for H2S and CS, were at mixing ratios < 25 pptv and < 10 pptv, respectively, with a maximum mixing ratio of about 100 pptv and 50 pptv, respectively. Carbonyl su lfide intercomparisons were at mixing ratios between 400 and 600 pptv. Measurements were intercompared from data bases constructed from time periods of simultaneous or overlapping measurements. Agreement among the COS techniques averaged about 5%, and individual measurements were generally within 10%. For H2S and at mixing ratio > 25 pptv, the inst ruments agreed on average to about 15%. At mixing ratios < 25 pptv the agreement was about 5 pptv. For CS2 (mixing ratios < 50 pptv), two te chniques agreed on average to about 4 pptv, and the third exhibited a bias (relative to the other two) that varied in the range of 3-7 pptv. CS2 mixing ratios over the ocean east of Natal as measured by the gas chromatograph-mass spectrometer technique were only a few pptv and we re below the detection limits of the other two techniques. The CITE 3 data are used to estimate the current uncertainty associated with airc raft measurements of COS, H2S, and CS2 in the remote troposphere.