Chloroform – concentration gradients in soil air and atmospheric air, and emission fluxes from soil

Since we demonstrated the natural formation of chloroform in soil, the question arose to which extent this contributes to the chloroform present in the atmosphere. Concentration gradients in soil air and atmospheric air of different forests were measured. Chloroform concentration gradients indicating emission occur in forest soils and the atmosphere under the canopy, whereas this was not observed for other chlorinated solvents. Above the canopy all concentration gradients observed for chloroform and 1,1,1-trichloroethane indicate deposition. The emission flux was measured using enclosures and calculated from the observed concentration gradients in soil air and atmospheric air. Wood-degrading areas and soils with a humic layer were found to emit up to 1000 ng chloroform m−2 h−1 and seem to be larger chloroform sources than the other areas of study. Rather unexpectedly, some points of one sampling site appeared to emit 1,1,1-trichloroethane, tetrachloromethane and tetrachloroethene. A reasonable agreement was found between the fluxes using enclosures and those derived from the concentration gradients in soil air and atmospheric air.