OVERVIEW OF AN AIRCRAFT EXPEDITION INTO THE BRAZILIAN CERRADO FOR THEOBSERVATION OF ATMOSPHERIC TRACE GASES

Tropospheric trace gases were measured from an aircraft platform. The flights were organized to sample air masses from the geographic area o f central Brazil, where the vegetation, a savanna-type environment wit h the local name of ''cerrado'', is subject to burning every year, esp ecially through August, September, and October. These measurements wer e made as a Brazilian local contribution to the international field ca mpaign organized by NASA, the Transport and Atmospheric Chemistry Near the Equator-Atlantic (TRACE A) mission, and the Southern African Fire Atmospheric Research Initiative (SAFARI). The major NASA TRACE A miss ion used the NASA DC 8 aircraft, with most flights over the South Atla ntic Ocean region. In Brazil, missions using small aircraft measured o zone and carbon dioxide continuously, and carbon monoxide, nitrous oxi de, and methane using grab sampling. In addition, ground-based measure ments were made continuously over most of the dry months of 1992, and ozonesondes were launched at three different sites. Geostationary Oper ational Environment Satellite-East (GOES E) images and a special netwo rk of radio soundings provided meteorological information, and advance d very high resolution radiometer (AVHRR) images indicated the distrib ution of fire pixels in the region of interest. Most of the biomass bu rning in 1992 occurred in the state of Tocantins, with about 22% of al l the burning in Brazil. The state of Mate Grosso was second, with 19% of all burning. The Brazilian aircraft was used mostly in these two s tates, near the cities of Porto Nacional and Cuiaba, for in situ sampl ing; 31 vertical profiles were made in air masses considered to be wel l mixed, that is, not in fresh plumes. Although the major interest was the dry season, sampling was also made during the previous wet season period in April 1992 for comparison; 10 vertical profiles were obtain ed using the same aircraft and measurement techniques. There is a clea r difference between these two opposite seasonal periods, most evident in the O-3 and CO data. Both Cuiaba and Porto Nacional show some 30-6 0 parts. per billion by volume (ppbv) larger methane concentrations, f or example, during the dry season, in comparison to the wet season, th e difference at Cuiaba being larger. The methane data for the wet seas on show no significant differences between Cuiaba and Porto Nacional m ixing ratios, which seems to exclude the existence of significant sour ces or sinks at these sites during this wet season. The ozone mixing r atios vary around 15 +/- 5 ppbv in the wet season, and from a minimum of 35 to a maximum of 70 +/- 10 ppbv, depending on height, in the dry season. The largest variability is seen in the carbon monoxide mixing ratios which vary from 90-100 ppbv in the wet season to maxima of 300 at 3.3 km and 600 ppbv at 1.2 km height in the dry season.