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Insights into the Peroxide-Bicyclic Intermediate Pathway of Aromatic Photooxidation: Experimental Yields and NO-Dependency of Ring-Opening and Ring-Retaining Products. | LitMetric

Insights into the Peroxide-Bicyclic Intermediate Pathway of Aromatic Photooxidation: Experimental Yields and NO-Dependency of Ring-Opening and Ring-Retaining Products.

Environ Sci Technol

State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China.

Published: December 2023

AI Article Synopsis

  • * This study found that the peroxide-bicyclic intermediate pathway is the dominant process in the oxidation of alkylbenzenes, significantly affecting the yields of various products generated during reactions with hydroxyl radicals (OH) and nitrogen oxides (NO).
  • * The research revealed that yields of bicyclic nitrates were lower than expected, and introduced new findings on carbonyl olefinic acids, highlighting complex interactions between different chemical reactions and shedding light on why there are differences between experimental and model predictions.

Article Abstract

Aromatic hydrocarbons are important contributors to the formation of ozone and secondary organic aerosols in urban environments. The different parallel pathways in aromatic oxidation, however, remain inadequately understood. Here, we investigated the production yields and chemical distributions of gas-phase tracer products during the photooxidation of alkylbenzenes at atmospheric OH levels with NO present using high-resolution mass spectrometers. The peroxide-bicyclic intermediate pathway emerged as the major pathway in aromatic oxidation, accounting for 52.1 ± 12.6%, 66.1 ± 16.6%, and 81.4 ± 24.3% of the total OH oxidation of toluene, m-xylene, and 1,3,5-trimethylbenzene, respectively. Notably, the yields of bicyclic nitrates produced from the reactions of bicyclic peroxy radicals (BPRs) with NO were considerably lower (3-5 times) than what the current mechanism predicted. Alongside traditional ring-opening products formed through the bicyclic pathway (dicarbonyls and furanones), we identified a significant proportion of carbonyl olefinic acids generated via the 1,5-aldehydic H-shift occurring in subsequent reactions of BPRs + NO, contributing 4-7% of the carbon flow in aromatic oxidation. Moreover, the observed NO-dependencies of ring-opening and ring-retaining product yields provide insights into the competitive nature of reactions involving BPRs with NO, HO, and RO, which determine the refined product distributions and offer an explanation for the discrepancies between the experimental and model-based results.

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Source
http://dx.doi.org/10.1021/acs.est.3c05304DOI Listing

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