Measurements of N₂O, CF₂Cl₂, CFCl₃, CH₃CCl₃, CCl₄, and CH₃Cl in the Troposphere and Lower Stratosphere over North America

Abstract

Samples of tropospheric and stratospheric air were collected on aircraft flights between October 4 and October 13, 1976. The region of the atmosphere surveyed was over the North American continent (approximately 18°N to 65°N latitude). Samples were obtained at heights ranging from about 3, 000ft. to 45, 000ft. Measurements of N₂O, CF₂Cl₂, CFCl₃, CH₃CCl₃, and CCl₄ were made by GC/EC techniques, and of CH₃Cl by GC/MS. The latitudinal and height profiles of these trace gases are reported in this paper. Calculations based on these measurements yield the following average tropospheric concentrations: [N₂O]=(330±2) ppb v, [CF₂Cl₂]=(236±7) ppt v, [CFCl₃]=(140±5) ppt v, [CH₃CCl₃]=(145±25) ppt v, and [CCl₄]=(134±9) ppt v (where the ± values are the standard deviations). The N₂O mixing ratio decreases only slightly in the lower stratosphere. CF₂Cl₂ and CFCl₃ mixing ratios decrease by about 10% and 15% respectively, within 4km above the tropopause. CCl₄ mixing ratio declines by about 50% within 4km above the tropopause. CH₃CCl₃ mixing ratios also show a sharp decline above the tropopause, similar to that of CCl₄. CH₃Cl on the other hand displays almost no change in mixing ratio between the free troposphere and the lower stratosphere.