Advances on Atmospheric Oxidation Mechanism of Typical Aromatic Hydrocarbons

Abstract

Aromatic hydrocarbons are important precursors of ozone and secondary organic aerosols in the urban atmosphere, which have important impact on air pollution, climate change and human health. Thus the research on the oxidation mechanism of aromatic hydrocarbons has become one of the most challenging hotspots topics in atmospheric environmental chemistry. This paper reviews the recent studies of aromatic hydrocarbons oxidation mechanism, discusses the reaction channels and influencing factors during the oxidation process under high/low NOx conditions, and focuses on new discoveries and new theories in the studies of aromatic hydrocarbon oxidation reactions. In the atmosphere, the initiation of aromatic hydrocarbons is dominated by the reaction with the OH radicals. According to the different reaction products, the oxidation reaction of aromatic hydrocarbon is mainly divided into aldehyde pathway, phenolic pathway, bicyclic RO2 pathway and epoxide pathway. With the development of new theories such as the formation of polyhydroxy compounds by aldehyde pathway, alkoxy radical epoxidation reaction, intramolecular H-migration reaction of bicyclic peroxy radicals, 1,5-aldehydic H-shift reaction, and the generation of low-carbon products by CO-loss reaction, the understanding of aromatic hydrocarbons oxidation mechanisms has improved. However, due to the carbon missing and radical budgets imbalance problems in the existing oxidation mechanism, our understanding about the subsequent O3 and secondary organic aerosols formation mechanisms are very limited. Theoretical calculation and experiment are the main methods to study the oxidation mechanism of aromatic hydrocarbons. Mass spectrometry and spectroscopy are the dominant measurement techniques for the oxidation intermediates of aromatic hydrocarbons. Online mass spectrometry can capture the tracer intermediates at the molecular level, which plays an important role in revealing the oxidation mechanism of aromatic hydrocarbons. In recent years, tracer measurement technology, especially chromatography-mass spectrometry technology has developed rapidly. This open up a new direction for the accurate measurement of intermediates and the improvement of aromatic hydrocarbon oxidation mechanism. On this basis, improving aromatic hydrocarbons oxidation mechanism, paying attention to the carbon missing and radical budgets imbalance in the oxidation reaction, and exploring the environmental implication of aromatic hydrocarbons oxidation in the real atmospheric conditions are expected to become the important directions of aromatic hydrocarbon oxidation study

Mechanisms and Kinetics Studies of Butylated Hydroxytoluene Degradation to Isobutene

“…By combining the information from ESP, ALIE, and Fukui function f 0 ( r ), it is clear that the benzene ring on BHT and the tert -butyl group near the phenolic hydroxyl side are more likely to react with OH radicals. It is worth noting that it is consistent with related reports. ,, Although a large number of research studies show that BHT can form a variety of metabolites with the OH radical. However, the mechanism of BHT degradation in the environment to produce isobutene is unclear.…”

“…The oxidation of BHT can take place on the aromatic ring, and in the p -methyl, t -butyl groups . The hydroxyl radicals in the environment are very importantly related to the degradation of benzene compounds, , and the alkyl substituents on the benzene ring provide many active sites for hydrogen abstraction of OH radicals …”

“…4 The hydroxyl radicals in the environment are very importantly related to the degradation of benzene compounds, 4,20 and the alkyl substituents on the benzene ring provide many active sites for hydrogen abstraction of OH radicals. 20 3.1. Determine Reaction Sites.…”

“…It is worth noting that it is consistent with related reports. 4,20,23 Although a large number of research studies show that BHT can form a variety of metabolites with the OH radical. However, the mechanism of BHT degradation in the environment to produce isobutene is unclear.…”

“…The initiation of the oxidation reaction of BHT is dominated by hydroxyl radicals. , According to the previous studies, the H-abstraction process of the phenolic hydroxyl group in BHT is a barrierless process, but it is difficult for OH radicals to contact the phenolic hydroxyl group due to the steric effect of tert -butyl groups . Therefore, OH radicals can react with BHT by abstracting H atoms from tert -butyl groups or by adding to the aromatic ring …”