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Characterization of products formed from the oxidation of toluene and m-xylene with varying NO and OH exposure. | LitMetric

Characterization of products formed from the oxidation of toluene and m-xylene with varying NO and OH exposure.

Chemosphere

School of Geography, Earth & Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, United Kingdom. Electronic address:

Published: September 2023

AI Article Synopsis

  • * Experiments using a PAM chamber revealed that both ring-retaining and ring-opening compounds are produced from the oxidation of these VOCs, with toluene generating a higher number of ring-opening products.
  • * SOA yields were found to be higher under high-NO conditions compared to low-NO, and a compound called DHOPA, often associated with toluene oxidation, was also present in m-xylene oxidation, suggesting its use as a general tracer for both VOCs.

Article Abstract

Aromatic volatile organic compounds (VOCs) are an important precursor of secondary organic aerosol (SOA) in the urban environment. SOA formed from the oxidation of anthropogenic VOCs can be substantially more abundant than biogenic SOA and has been shown to account for a significant fraction of fine particulate matter in urban areas. A potential aerosol mass (PAM) chamber was used to investigate the oxidised products from the photo-oxidation of m-xylene and toluene. The experiments were carried out with OH radical as oxidant in both high- and low-NO conditions and the resultant aerosol samples were collected using quartz filters and analysed by GC × GC-TOFMS. Results show the oxidation products derived from both precursors included ring-retaining and -opening compounds (unsaturated aldehydes, unsaturated ketones and organic acids) with a high number of ring-opening compounds observed from toluene oxidation. Glyoxal and methyl glyoxal were the major ring-cleavage products from both oxidation systems, indicating that a bicyclic route plays an important role in their formation. SOA yields were higher for both precursors under high-NO (toluene: 0.111; m-xylene: 0.124) than at low-NO (toluene: 0.089; m-xylene: 0.052), likely linked to higher OH concentrations during low-NO experiments which may lead to higher degree of fragmentation. DHOPA (2,3-dihydroxy-4-oxo-pentanoic acid), a known tracer of toluene oxidation, was observed in both oxidation systems. The mass fraction of DHOPA in SOA from toluene oxidation was about double the value reported previously, but it should not be regarded as a tracer solely for oxidation of toluene as m-xylene oxidation gave a similar relative yield.

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Source
http://dx.doi.org/10.1016/j.chemosphere.2023.139002DOI Listing

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