Organic nitrates (RONO2) are relevant compounds in the atmosphere as they are involved in the NOx spread, thus related to the O3 and SOA production. For this reason, the study of the reactivity of RONO2 has a huge importance for achieving proper atmospheric pollutants predictions. So far, the studies of these compounds have only been focused on non-functionalized RONO2 fates in the gas phase, however, most of them are highly oxidised, with a relevant presence in condensed phases, as shown by recent field experiments. Moreover, these studies have mostly been performed with mixtures of RONO2 leading to a complicated chemistry where the contribution of the multiphasic processes is unclear. In particular, the reactivity of these compounds in the aqueous phase is still completely unknown, while in the last decade the relevance of aqueous processes on atmospheric chemistry has been shown. The present work deals with the atmospheric reactivity of several RONO2 within the aqueous phase by studying individual molecules. We have selected four RONO2: two commercial alkyl nitrates and two oxidised RONO2 which we have synthesized. We will present our methodology set up for the study of atmospheric relevant reactions as hydrolysis, direct photolysis and OH-oxidation in the aqueous-phase. A complete study has been performed by monitoring the reaction with a wide variety of analytical techniques. LC-UV, LC-MS, GC-MS and HPIC have been used for identifying and covering the time profiles of the reactants and products in the aqueous-phase. Online techniques such as PTR-MS and a NOx analyser have been coupled to the reactor to follow the exchange of the volatile compounds with the gas-phase. In addition, we have identified the intermediate radicals formed in the aqueous-phase by EPR. For OH-oxidation, we have determined precise kinetic rate constants by a new competitive kinetics method developed using an on-line mass spectrometry detection (PTR-MS). We have elucidated the mechanisms which take place in the reactions, and identified the main reaction products. The results reveal the influence of the functional groups on the reactivity of the organic nitrates. Furthermore, they show the extent to which the aqueous processing differs from the gas-phase reactivity. We have reported the formation of NO2- and NO3- through specific aqueous reactions and the formation of other highly oxidised compounds, thus implicating the connexion between SOA formation and aqueous phase reactivity.

Aqueous phase reactivity of polyfunctional organic nitrates under atmospheric conditions

2019 Fall National Meeting

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