TROPOZ-II - GLOBAL DISTRIBUTIONS AND BUDGETS OF METHANE AND LIGHT-HYDROCARBONS

One hundred atmospheric samples were collected aboard the French Carav elle research aircraft, during the TROPOZ II experiment (January 1991) . Tropospheric meridional distributions versus height were then derive d from 70 degrees N to 60 degrees S and between 0.25 lan and 11 km for methane, acetylene, ethane and propane. Areas of significant emission s were identified over northern latitudes with, for acetylene, maximum mixing ratios in the north (1.896 ppbv) more than 70 times higher tha n in background southern latitudes (0.025 ppbv). The influence of emis sions from biomass burning was also obvious in the tropical boundary l ayer. Significant dynamic phenomena led to high mixing ratio zones abo ve 8 or 10 lan even for the most reactive hydrocarbons. For the first time, simultaneous assessment of global tropospheric contents of sever al light hydrocarbons was carried out. Using TROPOZ II data (January 1 991) and STRATOZ III data (June 1984) collected by Rudolph (1988) duri ng similar aircraft flights in 1988, the following tropospheric loads (in Tg-compound) were estimated, in January 1991 and June 1984, respec tively: 1.1 and 0.4 for acetylene, 5.0 and 3.9 for ethane, 3.6 and 1.4 for propane and 3545 for methane in January only. According to our re sults, 40 to 65% of acetylene and alkanes are oxidized in the tropics. In addition, by computing the annual tropospheric sink of acetylene a nd alkanes, an evaluation of their annual global fluxes was performed. The figures are, in Tg-compound y(-1) with an uncertainty of 80% to a n order of magnitude, based on January and June data, respectively: 10 and 6.6 for acetylene, 16.3 and 17.6 for ethane and 52.3 and 26.5 for propane.