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Upper ocean free radical chemistry
Applied Geochemistry, Vol. 3, p. 59, I988
0883-2927/88 $3.00 + ,00 Pergamon Press plc
Printed in Great Britain
Upper ocean free radical chemistry NEIL V. BLOUGH Department of Chemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, U.S.A.
THE OCEANS contain a vast, complicated array of chemical species. Heterogeneity is also apparent in the size distribution of these materials: they range from low to high molecular weight soluble compounds and extend up to microscopic and even macroscopic aggregates. It is likely that many (perhaps most) organic chromophores capable of sensitizing radical formation are part of high molecular weight or aggregated materials. In this situation the primary photochemistry, as well as many secondary reactions, presumably occurs within the matrix of the material. The extent to which photochemical equivalents are transferred to components in the external aqueous phase will depend on such factors as the kinetics of "intramolecular" recombination and disproportionation, the concentration of external electron donors/acceptors and their rates of diffusion into the matrix, and/or the ability of donors/acceptors to interact with the material through strong nonbonding interactions (e.g. hydrophobic association).
Also, the local properties of these microscopic reaction sites may differ dramatically from those of the surrounding aqueous phase. These differences could lead to reactions that normally would be unexpected for an aqueous milieu. For example, superoxide is a poor nucleophile in water, but a powerful one in aprotic environments. These possibilities are the basis for the following questions for discussion: (1) Do heterogeneous reaction pathways dominate oceanic free radical chemistry and photochemistry, or do they play only a minor role? How might this be tested? (2) What techniques are available for measuring "localized" or interfacial reactions? What are their levels of sensitivity? (3) Similar chemical processes may take place at the air-sea boundary. What new technologies are available for examining (photo) chemical reactions in surface films and monolayers?
59 AG 3 : l - g
0883-2927/88 $3.00 + ,00 Pergamon Press plc
Printed in Great Britain
Upper ocean free radical chemistry NEIL V. BLOUGH Department of Chemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, U.S.A.
THE OCEANS contain a vast, complicated array of chemical species. Heterogeneity is also apparent in the size distribution of these materials: they range from low to high molecular weight soluble compounds and extend up to microscopic and even macroscopic aggregates. It is likely that many (perhaps most) organic chromophores capable of sensitizing radical formation are part of high molecular weight or aggregated materials. In this situation the primary photochemistry, as well as many secondary reactions, presumably occurs within the matrix of the material. The extent to which photochemical equivalents are transferred to components in the external aqueous phase will depend on such factors as the kinetics of "intramolecular" recombination and disproportionation, the concentration of external electron donors/acceptors and their rates of diffusion into the matrix, and/or the ability of donors/acceptors to interact with the material through strong nonbonding interactions (e.g. hydrophobic association).
Also, the local properties of these microscopic reaction sites may differ dramatically from those of the surrounding aqueous phase. These differences could lead to reactions that normally would be unexpected for an aqueous milieu. For example, superoxide is a poor nucleophile in water, but a powerful one in aprotic environments. These possibilities are the basis for the following questions for discussion: (1) Do heterogeneous reaction pathways dominate oceanic free radical chemistry and photochemistry, or do they play only a minor role? How might this be tested? (2) What techniques are available for measuring "localized" or interfacial reactions? What are their levels of sensitivity? (3) Similar chemical processes may take place at the air-sea boundary. What new technologies are available for examining (photo) chemical reactions in surface films and monolayers?
59 AG 3 : l - g