Chemical characteristics of tropospheric air over the tropical South Atlantic ocean: Relationship to trajectory history

The TRACE A (Transport and Atmospheric Chemistry Near the Equator-Atlantic) experiment was designed to explore the atmospheric chemistry and meteorology over the tropical South Atlantic Ocean with a focus on the impact of South American and African biomass burning and continental outflow on the region. TRACE A was conducted in September/October 1992. Companion papers in this special issue show that the chemical composition of tropospheric air throughout the region is strongly impacted by biomass burning and outflow from both continents. This paper shows similar results and examines the chemical composition of air measured during NASA DC-8 aircraft ascents/descents at locations along the coast of both continents as well as at mid-Atlantic Ocean locations. Chemical composition of the air and backward trajectory calculations are used to illustrate the influences of continental outflow and how influences change with location throughout the region. Included in the examples are data which show that air along the Atlantic coast of Africa is impacted by outflow from both South America and Africa as air at the higher altitudes (e.g., 8 to 10 km) originates from South America, while lower-altitude air is from African sources. Of additional interest are data measured over the Indian Ocean near the tip of Africa which show aged air from South America being impacted by biomass burning emissions as the air passes over Africa 1 to 2 days prior to sampling.