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Kinetics of the Nitrite to Nitric Oxide Reaction in Peat

Dep. of Chemistry and Biochemistry, Univ. of Windsor, Windsor, Ontario, Canada N9B 3P4

W. J. Findlay

Agriculture Canada Res. Stn., Harrow, Ontario, Canada, N0R 1G0

* Corresponding author.

ABSTRACT

Nitrite consumption and net NO production rates were measured across a pH range of about 3 to 8 and a temperature range of 5 to 40 or 10 to 70°C in nonsterile and sterile peat, respectively. The NO was sparged from stirred peat/water (1:10) slurries by N₂ or Ar carrier gas and analyzed. Addition of small quantities, 1 to 280 µg NO^-₂-N g^–1 dry peat, resulted in immediate No production. Biological production of NO exceeded chemical (nonbiological) production in nonsterile peat at pH >5. At pH >6, rates were less than 5 x 10^–9 mol min^–1 g^–1 dry peat with chemical production rates relatively insignificant. Decreasing pH increased rates significantly, particularly the nonenzymatic process, which apparently dominates NO production at pH <4.5. The chemical process was first order with respect to [NO^-₂]. The dependence of [H⁺] was complex, approximating first-order behavior at [H⁺] <4 x 10^–4 mol g^–1 dry peat and more strongly dependent at higher concentrations. The activation energy for the chemical reaction at pH 5.09 was 52.3 kJ mol^–1. The average value for nonsterile peat measured at pH 5.45 and 6.26 was 41.4 kJ mol^–1. The stoichiometric coefficient, a, for the overall reaction NO^-₂ a No was 2.14 ± 0.39 in sterile peat and 2.00 ± 0.38 in nonsterile peat. In the latter case, where both enzymatic and nonenzymatic reactions occur, the value may also reflect the nonenzymatic reaction. Other nitrogenous gases, N₂O, N₂, NO_x and CH₃ONO were not observed under the flow conditions employed, suggesting that NO is the primary product of NO^-₂ reduction.

Some of this work was presented at the Workshop on Role of Canadian Wetlands in the Atmospheric Cycles of C, N, and S; Canadian Institute for Research in Atmospheric Chemistry; Atmospheric Environment Service; Toronto, Ontario; 27–29 Jan. 1988.

Received for publication February 6, 1989.