NASA GTE TRACE-A EXPERIMENT (SEPTEMBER OCTOBER 1992) - OVERVIEW

An overview of the Transport and Atmospheric Chemistry near the Equato r-Atlantic (TRACE A) field mission is presented. TRACE A was conducted to provide a comprehensive investigation of the chemical composition, transport, and chemistry of the atmosphere over the tropical South At lantic Ocean and the adjacent South American and African continents. M easurements for TRACE A consisted of a remote sensing component to der ive tropospheric ozone and biomass burning patterns, an airborne atmos pheric chemistry component to determine the composition of the air in the most pristine areas of our research domain as well as to character ize the photochemistry and transport of trace gas emissions from both fire and biogenic sources, a series of ozonesonde observations, and an enhanced radiosonde network and airborne meteorological measurements that provided information about the transport of trace gases and the p hysical processes that were responsible for their observed distributio ns. The data were interpreted through the use of both photochemical an d meteorological numerical models. The picture that emerges from TRACE A is that widespread biomass burning in both South America and southe rn Africa is the dominant source of the precursor gases necessary for the formation of the huge amounts of ozone over the South Atlantic Oce an. In addition, however, the meteorology in this region of the world is favorable for the accumulation of these pollutants over the tropica l Atlantic basin so that photochemical processes produce large quantit ies of ozone in situ. The generation of ozone occurs over scales of th ousands of kilometers and is unusually enhanced in the upper troposphe re where relatively high concentrations of nitrogen oxides (NOx) preva il. This latter finding suggests that convective processes (or other l ifting mechanisms) may play an important role in the generation of tro pospheric ozone or that there may be an additional significant upper t ropospheric source of NOx, such as from lightning.