Pos, W. H. Universidade Federal de Mians Gerais/EE-DESA, whpos@net.em.com.br
Riemer, D. H. National Center for Atmospheric Research/ACD, riemer@acd.ucar.edu
Zika, R. G. University of Miami/RSMAS, rzika@rsmas.miami.edu

 
FURTHER EVIDENCE OF FREE RADICAL PARTICIPATION ON HYDROGEN SULFIDE SPECIES OXIDATION IN NATURAL WATERS
 
Photoreaction of hydrogen sulfide species in natural waters involves a complex mechanism. Free radical reactions have been suggested as one of the major pathways by which hydrogen sulfide species undergo oxidation. Metal catalysis is a potential generator of free radicals through redox reactions. In these experiments, sulfide photooxidation rates obtained with Biscayne Bay seawater (BBSW) that had been treated to reduce metal content by filtration through a Dowex column were much lower than those obtained from untreated BBSW. The relative rates (k) calculated from the slope of ln[sulfide] vs time indicated a decrease on the order of 50% for samples that had been filtered compared to those that had not. However, DOC analyses of both samples showed a reduction in DOC concentration in the treated sample relative to the untreated sample. The ratio (DOC(unfilt)/DOC(filt)) was strictly proportional to the ratio of sulfide photooxidation rate (k(unfilt)/k(filt)). These experiments demonstrate that metal-DOM interactions are complex and cannot be regarded as separate processes when studying DOM related reactions in natural waters. Preliminary calculations show that the pathway involved in the sulfide photooxidation is primarily driven by free radical reactions. This is based on the low value of Eact (14.8 +/- 2.8) kJ/mol) obtained from the Arrhenius plot. The low Eact value obtained here demonstrates the ease with which photochemical transformations occur in seawater.
 
Day: Thursday, Feb. 4
Time: Poster
Location: Sweeney Center
 
Code: SS37TH0974S