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 ques tion arose to which extent this contributes to the chloroform present in th e atmosphere. Concentration gradients in soil air and atmospheric air of di fferent forests were measured. Chloroform concentration gradients indicatin g emission occur in forest soils and the atmosphere under the canopy, where as this was not observed for other chlorinated solvents. Above the canopy a ll concentration gradients observed for chloroform and 1,1,1-trichloroethan e indicate deposition. The emission flux was measured using enclosures and calculated from the observed concentration gradients in soil air and atmosp heric 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, tetrachloromethan e and tetrachloroethene. A reasonable agreement was found between the fluxe s using enclosures and those derived from the concentration gradients in so il air and atmospheric air. (C) 2000 Elsevier Science Ltd. All rights reser ved.