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. Multifunctional organic nitrates, including carbonyl nitrates, are importantspecies formed in NOx-rich atmospheres by the degradation of volatile organic compounds (VOCs). Thesecompounds have been shown to play a key role in the transport of reactivenitrogen and, consequently, in the ozone budget; they are also known to be importantcomponents of the total organic aerosol. However, very little is known abouttheir reactivity in both the gas and condensed phases. Following a previousstudy that we published on the gas-phase reactivity of α-nitrooxyketones, the photolysis and reaction with OH radicals of4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone (which are a β-nitrooxy ketone and γ-nitrooxy ketone, respectively) were investigated for thefirst time in simulation chambers. The photolysis frequencies were directlymeasured in the CESAM chamber, which is equipped with a very realisticirradiation system. The jnitrate/jNO2 ratios were found to be (5.9±0.9)×10-3 for 4-nitrooxy-2-butanone and (3.2±0.9)×10-3 for 5-nitrooxy-2-pentanone under our experimentalconditions. From these results, it was estimated that ambient photolysisfrequencies calculated for typical tropospheric irradiation conditionscorresponding to the 1 July at noon at 40∘ N (overhead ozone column of 300 and albedo of 0.1) are (6.1±0.9)×10-5 s−1 and (3.3±0.9)×10-5 s−1 for 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone, respectively.These results demonstrate that photolysis is a very efficient sink for thesecompounds with atmospheric lifetimes of few hours. They also suggest that,similarly to α-nitrooxy ketones, β-nitrooxy ketones haveenhanced UV absorption cross sections and quantum yields equal to or close tounity and that γ-nitrooxy ketones have a lower enhancement of crosssections, which can easily be explained by the larger distance between thetwo chromophore groups. Thanks to a product study, the branching ratio betweenthe two possible photodissociation pathways is also proposed. Rateconstants for the reaction with OH radicals were found to be (2.9±1.0)×10-12 and (3.3±0.9)×10-12 cm3 molecule−1 s−1,respectively. These experimental data are in good agreement with rateconstants estimated by the structure–activity relationship (SAR) of Kwok and Atkinson (1995) when using theparametrization proposed by Suarez-Bertoa et al. (2012) for carbonylnitrates. Comparison with photolysis rates suggests that the OH-initiatedoxidation of carbonyl nitrates is a less efficient sink thanphotodissociation but is not negligible in polluted areas.

Photolysis and oxidation by OH radicals of two carbonyl nitrates: 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone