THE TROPOSPHERIC DISTRIBUTION OF CARBON-MONOXIDE AS OBSERVED DURING THE TROPOZ-II EXPERIMENT

As part of the TROPOZII large-scale measurement campaign in January 19 91 we deployed a Four Laser Airborne Infra Red (FLAIR) tunable diode l aser spectrometer on board a Caravelle 116 research aircraft. We repor t here in situ CO measurements which were obtained with one of the fou r channels of the FLAIR instrument at a time resolution of either one or two minutes. The flight route of the TROPOZ II campaign followed th e Atlantic coasts of North America, the Pacific and Atlantic coasts of South America and the Atlantic coasts of West Africa and Europe. A to tal of 48 CO vertical profiles extending from the surface to 10.5 km a ltitude were obtained. Ln the meridional direction adjacent profiles w ere separated by less than 10 degrees latitude. Polewards of 30 degree s S the CO distribution was very homogeneous with a mean mixing ratio of 55 ppbv. Between 30 degrees S and the equator, the CO mixing ratio above 8 km altitude ranged up to 130 ppbv and was 20-60 ppbv higher th an in the mid free troposhere. Three day backward trajectories for the se CO rich airmasses originated over Amazonia. Earlier trace gas measu rements as well as circulation studies suggested that these airmasses were of Northern Hemispheric origin and had been rapidly convected to the upper troposphere over central South America. The influence of bio mass burning is clearly apparent from the measurements performed at 10 degrees N on the African side of the Atlantic with CO mixing ratios b eing 100-300% higher than on the Central American side. CO mixing rati os further north ranged from 80 to 130 ppbv in the free troposphere an d increased to 130-150 ppbv at lower altitudes.