Meridional and vertical CO and CH4 distributions in the background troposphere (70°N-60°S; 0–12 km altitude) from scientific aircraft measurements during the stratoz III experiment (June 1984)

Abstract

During the STRATOZ III experiment (June 1984) designed for a study of trace gases in the atmosphere, more than 2000 concurrent measurements of CO and CH₄ by gas chromatography were obtained from a series of flights aboard a scientific aircraft “Caravelle 116” between 70°N and 60°S, and up to a cruising altitude of 12 km, over the Atlantic Ocean and along the American, African and European continents.

While a global interpretation of the data must await the examination of the whole series of compounds measured, a preliminary analysis of the results obtained for CO and CH₄ is reported here.

The CO and CH₄ mixing ratios are found to be higher in the Northern Hemisphere than in the Southern, which reflects the meridional distribution of their sources and the influence of tropospheric photochemistry. A prominent CO difference between the two hemispheres is observed in the continental air (NH: 100–200 ppb; SH: 80–90 ppb) while the oceanic air is much more homogeneous (NH: 80–90 ppb; SH: 60–70 ppb). In the case of CH₄, a regular decrease is observed between the high latitudes of the Northern Hemisphere and those of the Southern.

For the Southern Hemisphere, the CO values are in agreement with literature data, but for the Northern they are lower than previously reported. The CH₄ results suggest the possible existence of natural sources in the Southern Hemisphere (Amazonia; South Pacific).

A comparison of the measurements made in the Southern Hemisphere with reliable data sets previously reported in the literature confirms an increase rate of 1.2 ± 0.3 % per year for CH₄, but does not provide any evidence for a long term variation of the CO content.

The comprehensive data reported here will be of valuable interest to improve the understanding of the physico-chemistry of the troposphere and its evolution.