OZONE AND AEROSOL DISTRIBUTIONS AND AIR-MASS CHARACTERISTICS OVER THESOUTH-ATLANTIC BASIN DURING THE BURNING SEASON

In situ and laser remote measurements of gases and aerosols were made with airborne instrumentation to investigate the sources and sinks of tropospheric gases;md aerosols over the tropical South Atlantic during the NASA Global Tropospheric Experiment (GTE)/Transport and Atmospher ic Chemistry Near the Equator-Atlantic (TRACE A) field experiment cond ucted in September-October 1992. Gases from extensive fires in Brazil were transported by convective storms into the upper troposphere where tropospheric ozone (O-3) was photochemically produced and advected ea stward over the South Atlantic. In central Africa, the fires were wide spread, and in the absence of deep convection, the fire plumes were ad vected at low altitudes (below similar to 6 lan) over the Atlantic, Th ere was a positive correlation between O-3 and aerosols found in the p lumes that were not involved in convection. High O-3 (>75 parts per bi llion by volume (ppbv)) was observed in the low-altitude plumes, and a lso in the upper troposphere where O-3 often exceeded 100 ppbv with lo w aerosol loading. The average tropospheric O-3 distributions were det ermined for the following: Brazil and western South Atlantic, eastern and central South Atlantic, central and east coast of Africa, and the entire South Atlantic Basin. The tropopause heights and O-3 columns ac ross the troposphere were calculated for individual flights and for th e average O-3 distributions in the above regions. A maximum tropospher ic O-3 column of 56 Dobson units (DU) was found over the biomass burni ng region in Zambia and in the subsidence region over the central Sout h Atlantic. The high O-3 region over the South Atlantic from 4 degrees to 18 degrees S corresponded with the latitudinal extent of the fires in Africa. In situ and laser remote measurements were used to determi ne the frequency of observation and chemical composition of nine major air mass types. Biomass burning emissions contributed to most of the air masses observed over the South Atlantic Basin, and biomass burning was found to contribute up to half (28 DU) of the O-3 column across t his region.