Theoretical studies of atmospheric reaction mechanisms in the troposphere

Abstract

The chemistry of the atmosphere encompasses a vast number of reactions acting on a plethora of intermediates. These reactions, occurring sequentially and in parallel, give rise to intertwined and irreducible mechanisms describing the complex chemical transformations of organic and inorganic compounds in the atmosphere. The complexity of this system is that it requires combined experimental, theoretical, and modeling approaches to elucidate the characteristics of the individual reactions, and their mutual interaction. In this review, we describe recent results from quantum chemical and theoretical kinetic studies of relevance to atmospheric chemistry. The review first summarizes the most commonly used theoretical methodologies. It then examines the VOC oxidation initiation channels by OH, O(3), NO(3) and Cl, followed by the reactions of the alkyl, alkoxy, alkylperoxy and Criegee intermediates active in the subsequent oxidation steps. Specific systems such as the oxidation of aromatics and the current state of knowledge on OH-regeneration in VOC oxidation are also discussed, as well as some inorganic reactions.

Role of the reaction of stabilized Criegee intermediates with peroxy radicals in particle formation and growth in air

“…It can be seen in Fig. 2b and c that the presence of formic acid, which reacts with SCI, 5,45,[66][67][68] strongly suppresses the formation of longer oligomers, confirming that SCI play a key role in oligomer formation.…”

“…45,67,68,[72][73][74] In order to evaluate the influence of water vapor on both oligomer and new particle formation from ozonolysis, we conducted chamber experiments over a wide range of relative humidities using 800 ppb trans-3-hexene and 1.5 ppm O 3 . Fig.…”

“…In addition, SCI react with a number of other atmospheric species, e.g., H 2 O, SO 2 , NO 2 , carboxylic acids, as well as carbonyl and hydroxyl compounds. 5,45,[66][67][68]72,[93][94][95] Bimolecular reactions with these scavengers, in particular H 2 O, have been suggested to be the dominant loss pathway of some SCIs in the atmosphere. 45,67,72 However, in the present study, water vapor was shown to increase new particle formation while decreasing the total mass.…”

Communication: Thermal unimolecular decomposition of syn-CH3CHOO: A kinetic study

“…In addition to providing additional sources of hydroxyl radicals at night, it also produces organic compounds that can then lead to the formation of aerosols and particulates. [1][2][3][4][5][6] Therefore, understanding the mechanism and kinetics of the elementary ozonolysis reactions is fundamentally important to atmospheric chemistry and kinetic models.…”

“…[1][2][3][4][5][6] Hot CIs have sufficient internal energies to undergo prompt H-migration and/or ring-closure, leading to formations of OH radicals and/or organic acids/esters, respectively. 7 Cold CIs, in contrast, have insufficient internal energies to undergo fast unimolecular reactions, 7 and thus, their lifetimes are much longer than those of hot CIs.…”