Atmospheric fate and deposition of polychlorinated dibenzo-p-dioxins and dibenzofurans.

摘要

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) are introduced into the atmosphere from a variety of combustion sources and become dispersed throughout the environment. The PCDD/F homologue profiles of sources, represented by municipal and industrial waste incineration effluents, are (on average) characterized by an almost uniform homologue profile of PCDD/F. In contrast, sink profiles, represented by sediments, are dominated by octachlorodibenzo-p-dioxin (8D). Both degradation and deposition processes could account for this change in homologue profile. In this thesis, we investigate how photodegradation of particle-bound PCDD/F, wet deposition, and dry deposition contribute to the observed changes in PCDD/F homologue profiles.;Sampling methods included the use of wet-only samplers to collect rain and the use of inverted frisbees and flat plates to collect dry deposition. Samples were prepared for analysis by silica gel and alumina column chromatography and were analyzed by electron capture, negative ionization, gas chromatographic mass spectrometry.;We first studied the photodegradation of PCDD/F adsorbed to various fly ashes (surrogate atmospheric particles) using a rotary photoreactor illuminated with a 450 W, medium-pressure mercury vapor lamp. The results of these experiments suggest that airborne, particle-bound PCDD/F do not photodegrade.;Rain was collected in Indianapolis, Indiana. Dissolved phase and particle-bound PCDD/F were measured separately. The average, total wet deposition flux of PCDD/F in Indianapolis was 160 ng/(m;Dry deposition fluxes were measured in Bloomington, Indiana, and Indianapolis. The average dry deposition flux in Bloomington was 100 ng/(m;Our results indicate that the changes in PCDD/F homologue profiles are not caused by photodegradation of particle-bound PCDD/F. However, both wet and dry deposition, which are important mechanisms for the removal of atmospheric PCDD/F, contribute to the enhancement of 8D observed in the sediments.