NITRITE PHOTOLYSIS IN SEAWATER BY SUNLIGHT

Nitrite is chemically stable but photochemically unstable in seawater. The net disappearance rate in abiotic low-nitrate seawater exposed to sunlight is ∼ 10% per day. The primary products are the free radicals NO and OH. Quantitative aspects of the kinetics and secondary product formation are discussed in terms of a fourteen-step reaction scheme. Possible pathways explaining the results are suggested but not unequivocally identified. The rate of reaction in various marine environments is estimated from cruise data and extrapolations to vary between 0.2-60·10-3 moles m-2yr-1, with a suggested global average for comparison purposes of 1-10·103 moles m-2yr-1. These results confirm and quantify our previous suggestion that nitrite photolysis represents a source of OH radical in seawater. The reaction rate is large enough that significant impacts on the geochemical cycles of dissolved organic carbon and nitrogen and heavy metals may plausibly result. Effects on marine biota and atmospheric trace gas composition are also possible. However, specific reactions coupling the nitrite system to other processes have not yet been identified or demonstrated empirically. © 1979.