The oxidation of NO₂ to nitrate-day and night

Abstract

In a recent article Richards (1983) has suggested a chemical reaction mechanism, given in Table 1, for night-time NO₂ oxidation. Richards makes several qualitative statements concerning the ability of this mechanism to represent measured night-time NOₓ concentrations but does not present simulated results based on this mechanism. In order to assess the validity of Richards' suggested mechanism, we have integrated the rate equations corresponding to the reactions in Table 1 under the following conditions: (1) There is a constant source of NO, S_(NO) (ppm min⁻¹) during the night, (2) At t = 0 (1800 PDT) the initial concentrations are those reported by Platt et al. (1980) from the Los Angeles area. These initial conditions are summarized in Table 2. Since the NO concentration at 1800 PDT was not reported by Platt et al. (1980), to obtain an initial condition we have assumed that the concentration of NO at this time can be obtained from the NO₂ and O₃ concentrations through the photostationary state relation with an approximate NO₂ photolysis rate of 0.1 min⁻¹. The NO emission flux, S_(NO) must be specified to carry out the calculation, and we have considered values typical for Los Angeles. The object of our calculation is, as we noted above, to ascertain if the reaction set in Table 1 is capable of explaining observed night-time NOₓ chemistry.

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