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

Abstract

Abstract. Multifunctional organic nitrates, including carbonyl nitrates, are important species formed in NOx-rich atmospheres by the degradation of volatile organic compounds (VOCs). These compounds have been shown to play a key role in the transport of reactive nitrogen and, consequently, in the ozone budget; they are also known to be important components of the total organic aerosol. However, very little is known about their reactivity in both the gas and condensed phases. Following a previous study that we published on the gas-phase reactivity of α-nitrooxy ketones, the photolysis and reaction with OH radicals of 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone (which are a β-nitrooxy ketone and γ-nitrooxy ketone, respectively) were investigated for the first time in simulation chambers. The photolysis frequencies were directly measured in the CESAM chamber, which is equipped with a very realistic irradiation 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 experimental conditions. From these results, it was estimated that ambient photolysis frequencies calculated for typical tropospheric irradiation conditions corresponding 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 these compounds with atmospheric lifetimes of few hours. They also suggest that, similarly to α-nitrooxy ketones, β-nitrooxy ketones have enhanced UV absorption cross sections and quantum yields equal to or close to unity and that γ-nitrooxy ketones have a lower enhancement of cross sections, which can easily be explained by the larger distance between the two chromophore groups. Thanks to a product study, the branching ratio between the two possible photodissociation pathways is also proposed. Rate constants 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 rate constants estimated by the structure–activity relationship (SAR) of Kwok and Atkinson (1995) when using the parametrization proposed by Suarez-Bertoa et al. (2012) for carbonyl nitrates. Comparison with photolysis rates suggests that the OH-initiated oxidation of carbonyl nitrates is a less efficient sink than photodissociation but is not negligible in polluted areas.

A comparative and experimental study of the reactivity with nitrate radical of two terpenes: <i>α</i>-terpinene and <i>γ</i>-terpinene

“…It is also expected that organic nitrates adsorb on the stainlesssteel walls. Indeed, the loss rates of several multifunctional organic nitrates (in particular carbonyl nitrates) have been observed in previous studies (Suarez-Bertoa et al, 2012;Picquet-Varrault et al, 2020) and were found to range between 0.5 and 2 × 10 −5 s −1 . However, as yields of organic nitrates in the gas phase were calculated during a relatively short period (less than 1 h), these wall losses are expected to be low (less than 10 %), and this is confirmed by the good linearity of the plots.…”

“…Since the early 1980s and the discovery of the nitrate radical (NO 3 ) in the nocturnal troposphere (Noxon et al, 1980;Platt et al, 1980) and stratosphere (Naudet et al, 1981;Noxon et al, 1978), nighttime chemistry has been known to be active. NO 3 is mainly formed by the reaction of nitrogen dioxide (NO 2 ) with ozone and has two very efficient sinks during the day, its photolysis and its reaction with NO (Brown and Stutz, 2012).…”

“…They therefore significantly influence the nitrogenous species (NO y ) and ozone budgets in these regions (Ito et al, 2007). Furthermore, some (multifunctional) organic nitrates are low-volatile and highly soluble in both the aqueous phase and organic aerosols (Picquet-Varrault et al, 2020) and are thus capable of strongly partitioning into the atmospheric condensed phases (droplets, aerosols). Recent field observations of the aerosol chemical composition have shown that organic nitrates range from 10 % to 75 % of total organic aerosol (OA) mass (Kiendler-Scharr et al, 2016;Lee et al, 2016;Xu et al, 2015), suggesting that these species are important components of OAs.…”

On the importance of atmospheric loss of organic nitrates by aqueous-phase ·OH-oxidation

“…We used the developed SAR to predict the kOH rate constants of other atmospherically relevant organic nitrates to evaluate if the aqueous-phase •OH-oxidation has a significant role on their atmospheric lifetimes. Some of the evaluated organic nitrates have been detected in field campaigns (Beaver et al, 2012;Li et al, 2018); they are expected products from isoprene or monoterpenes photooxidation (Lee et al, 2014); or they are small polyfunctional nitrates that may be formed by the fragmentation of terpene nitrates or by the oxidation of alkyl nitrates (Picquet-Varrault et al, 2020;Treves and Rudich, 2003). Selecting organic nitrates potentially relevant to atmospheric chemistry, as well as those mentioned in the literature, we listed 49 compounds that were divided into 7 categories depending on their functionalization and chemical structure: 6 alkyl nitrates, 7 hydroxy nitrates, 7 ketonitrates, 5 aldehyde nitrates, 5 nitrooxy carboxylic acids, 7 other polyfunctional nitrates containing more than one oxygenated group, and 12 terpene nitrates corresponding to highly oxidized organic nitrates formed by the oxidation of terpenes, such as α-and β-pinene, limonene and myrcene.…”

“…The gas-phase chemistry of organic nitrates has been studied through kinetic experiments focusing on their •OH-oxidation (Bedjanian et al, 2018;Picquet-Varrault et al, 2020;Treves and Rudich, 2003;Wängberg et al, 1996;Zhu et al, 1991) and direct photolysis (Clemitshaw et al, 1997;Picquet-Varrault et al, 2020;Suarez-Bertoa et al, 2012). These experiments provide data for different types of organic nitrates, including alkyl nitrates, ketonitrates, hydroxy nitrates, dinitrates, cyclonitrates and alkene nitrates, and provide knowledge on their gas-phase atmospheric fate.…”