Gas-Surface Interactions in Cryogenic Whole Air Sampling.
Abstract
Physico-chemical phenomena associated with in-situ cryogenic whole air sampling of stratospheric species (i.e., CF2CL2, CFCL3, N2, O2, O3, NO, NO2, N2O, and CO2) are examined. Condensation phenomena on disks of various materials, (e.g., electropolished, gold-flashed, and hexamethyldisilazane-coated stainless steel), cooled by a mechanical, helium cycle refrigerator, and subsequent thermal desorption behavior were studied using quadrupole mass spectrometry and NOx chemiluminescence. Strong, spurious 'first' condensations in the 200-250 K temperature range were observed for most of the species studied. This phenomenon is attributed to water vapor contamination of the surface, which affects both the temperature and mechanism of the subsequent 'true' thermodynamic condensation, resulting in supersaturation and condensate growth initiation by surface nucleation. Desorption spectra of binary cryofrosts and of the pure components revealed significant levels of interaction between species in the cryofrost. These results preclude chromatographic cryo-fractionation as a reliable technique for whole air sample analysis. Reactions which occur during cryofrost regeneration were studied via temperature programmed and flash desorption. Surprisingly persistent disproportionation of NO (i.e., 4NO yields N2 + 2NO2) occurred with conversions of nearly 50% upon desorption of NO- containing cryofrosts. Rapid ozone recombination and oxidation of NO to NO2 by ozone are also reported. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1981
- Accession Number
- ADA108255
Entities
People
- E. J. Dineen
- J. M. Calo
- R. J. Fezza