Seasonal trends of ozone in equatorial Africa: Experimental evidence of photochemical formation

Abstract

Surface ozone measurements obtained at Brazzaville, Congo (4°20′S, 15°20′E), from 1983 to 1986 are summarized. In addition, results from aircraft surveys (1985 and 1986) from Brazzaville to the Atlantic coast and results from a shipboard expedition (1986) along the Atlantic coast at the Equator are presented. On the basis of the data, there appears to exist a seasonal cycle with the highest values in early spring (southern) which compare with the mid‐latitude values observed in the northern hemisphere. The data suggest that during the dry season, emission of precursor gases from biomass burning leads to high ozone values in the boundary layer. Ozone mixing ratios approached levels as high as 100 parts per billion by volume in a layer residing just above the monsoon. In the wet season, the data suggest that biogenic, organic emissions may act as precursors to photochemical ozone production and may contribute to the fairly high ozone burden of the lower troposphere over Equatorial Africa.