AN INTERCOMPARISON OF INSTRUMENTATION FOR TROPOSPHERIC MEASUREMENTS OF DIMETHYL SULFIDE - AIRCRAFT RESULTS FOR CONCENTRATIONS AT THE PARTS-PER-TRILLION LEVEL

This paper reports results from NASA's Chemical Instrumentation and Te st Evaluation (CITE 3) during which airborne measurements of dimethyl sulfide (DMS) from six instruments were intercompared. Represented by the six instruments are three fundamentally different detection princi ples (flame photometric, mass spectrometric, and electron capture afte r fluorination); three collection/preconcentration methods (cryogenic, gold wool absorption, and polymer absorbent); and three types of oxid ant scrubbers (solid phase alkaline, aqueous reactor, and cotton). The measurements were made over the Atlantic Ocean in August/September 19 89 during flights from NASA's Wallops Flight Center, Virginia, and Nat al, Brazil. The majority of the intercomparisons are at DMS mixing rat ios < 50 pptv. Results show that instrument agreement is of the order of a few pptv for mixing ratios < 50 pptv and to within about 15% abov e 50 pptv. Statistically significant (95% confidence) measurement bias es were noted among some of the techniques. However, in all cases, any bias is small and within the accuracy of the measurements and prepare d DMS standards. Thus, we conclude that the techniques intercompared d uring CITE 3 provide equally valid measurements of DMS in the range of a few pptv to 100 pptv (upper range of the intercomparisons).