Vertical distributions of COS, CS₂, DMS and other sulfur compounds in a loblolly pine forest

Measurements of atmospheric COS, CS₂, DMS, SO₂ and aerosol sulfate and methanesulfonate (MSA) concentrations were conducted in a loblolly pine forest in central Georgia between July and September 1990. The daytime profiles obtained for the reduced sulfur gases (COS, CS₂, DMS) often showed significantly higher concentrations at the canopy level than above the forest canopy, indicating a net emission of these gases from the tree tops. No evidence was found for a net uptake of COS by the canopy during daytime. With one exception, all COS concentrations measured during the day were significantly higher than corresponding nighttime values. These results appear to be in conflict with recent studies suggesting a net uptake of atmospheric COS by plants during photosynthetic activity. Possible explanations for these different findings are discussed. Nighttime profiles indicated no major biosphere-atmosphere exchange of COS, CS₂ or DMS. Nighttime DMS concentrations were significantly higher than corresponding daytime values. A clear inverse relationship between the diel variations of DMS and MSA was observed, consistent with rapid photochemical oxidation of DMS under the given conditions.