Vertical profiles of ozone between 0 and 400 meters in and above the African equatorial forest

Abstract

Ozone concentrations have been measured in the northern Congo, near Impfondo (1°37 N, 18°04 E) during the DECAFE experiment in February 1988. This period corresponds to the dry season in the northern part of the equatorial region. The measurements were carried out simultaneously (1) at ground level in a large clearing, (2) inside the forest between 0 and 30 m, and (3) above the forest with a captive balloon flying up to 400 m. The results presented here are compared with the data obtained in the Mayombe forest in the southern part of Congo, near Dimonika in June 1988, during the dry season. For both northern and southern forested areas the ozone concentrations measured at ground level in a large clearing exhibit daily variations with maxima in the afternoon range between 10 and 30 parts per billion by volume (ppbv) and minima at the end of the night between 4 and 15 ppbv. The characterics of each surface ozone cycle are analyzed. Inside the forest, ozone concentrations are found very low near the ground and rarely exceed 15 ppbv above the canopy. At night the ozone concentrations are always close to zero at any level from the ground to the top of the canopy. Ozone removal processes are mainly located in the canopy. The ozone concentration above the forest is seen to increase in the early morning. Likely, this ozone production has a photochemical origin, the precursors coming from soils and biomass burning. The relationships among the vertical profiles of ozone, temperature, and water vapor are discussed.