Sulfur gases and aerosols in and above the equatorial African rain forest

Abstract

We determined the distribution of gaseous and particulate sulfur compounds in the canopy of the tropical rain forest of northern Congo and the overlying atmosphere during February 12–25, 1988. Hydrogen sulfide and dimethylsulfide decayed exponentially with altitude from approximately 30–40 ppt at ground level to 3–5 ppt at around 3 km altitude. Emission fluxes from the forest to the atmosphere were estimated by fitting a one‐dimensional time‐dependent numerical model of chemistry and transport of the sulfur compounds to their observed vertical profiles. Emission fluxes of 0.6–1.0 nmol HS m min and 0.3–0.7 nmol DMS m min were consistent with the observed vertical profiles of HS and DMS. These fluxes compare well with fluxes reported previously for the Amazon rain forest during the dry season and support the view of a subordinate role of land biota in the global cycling of sulfur. The particulate sulfur concentration of 248 ppt was found below the forest canopy. Biomass burning is considered to be an important contributor to this particulate sulfur. Carbonyl sulfide was found to be enhanced above the 500 ppt tropospheric background throughout the mixing layer of 2–3 km depth, likely due to biomass burning.