NO2 Suppression of Autoxidation–Inhibition of Gas-Phase Highly Oxidized Dimer Product Formation

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Rissanen , M P 2018 , ' NO2 Suppression of Autoxidation–Inhibition of Gas-Phase Highly Oxidized Dimer Product Formation ' , ACS Earth and Space Chemistry , vol. 2 , no. 11 , pp. 1211-1219 . https://doi.org/10.1021/acsearthspacechem.8b00123

Title: NO2 Suppression of Autoxidation–Inhibition of Gas-Phase Highly Oxidized Dimer Product Formation
Author: Rissanen, Matti P.
Other contributor: University of Helsinki, INAR Physics

Date: 2018-11
Language: eng
Number of pages: 17
Belongs to series: ACS Earth and Space Chemistry
ISSN: 2472-3452
DOI: https://doi.org/10.1021/acsearthspacechem.8b00123
URI: http://hdl.handle.net/10138/268477
Abstract: Atmospheric autoxidation of volatile organic compounds (VOC) leads to prompt formation of highly oxidized multifunctional compounds (HOM) that have been found crucial in forming ambient secondary organic aerosol (SOA). As a radical chain reaction mediated by oxidized peroxy (RO2) and alkoxy (RO) radical intermediates, the formation pathways can be intercepted by suitable reaction partners, preventing the production of the highest oxidized reaction products, and thus the formation of the most condensable material. Commonly, NO is expected to have a detrimental effect on RO2 chemistry, and thus on autoxidation, whereas the influence of NO2 is mostly neglected. Here it is shown by dedicated flow tube experiments, how high concentration of NO2 suppresses cyclohexene ozonolysis initiated autoxidation chain reaction. Importantly, the addition of NO2 ceases covalently bound dimer production, indicating their production involving acylperoxy radical (RC(O)OO•) intermediates. In related experiments NO was also shown to strongly suppress the highly oxidized product formation, but due to possibility for chain propagating reactions (as with RO2 and HO2 too), the suppression is not as absolute as with NO2. Furthermore, it is shown how NOx reactions with oxidized peroxy radicals lead into indistinguishable product compositions, complicating mass spectral assignments in any RO2 + NOx system. The present work was conducted with atmospheric pressure chemical ionization mass spectrometry (CIMS) as the detection method for the highly oxidized end-products and peroxy radical intermediates, under ambient conditions and at short few second reaction times. Specifically, the insight was gained by addition of a large amount of NO2 (and NO) to the oxidation system, upon which acylperoxy radicals reacted in RC(O)O2 + NO2 → RC(O)O2NO2 reaction to form peroxyacylnitrates, consequently shutting down the oxidation sequence. Keywords: acylperoxy radicals; Autoxidation; dimers; Highly oxidized multifunctional compounds; Highly oxygenated molecules; HOM; nitrogen oxides; peroxyacylnitrate
Subject: 116 Chemical sciences
Autoxidation
Highly oxidized multifunctional compounds
Highly oxygenated molecules
HOM
acylperoxy radicals
dimers
nitrogen oxides
peroxyacylnitrate
ATMOSPHERIC CHEMISTRY
PEROXY-RADICALS
PHOTOCHEMICAL OXIDATION
CHEMICAL-IONIZATION
OZONOLYSIS PRODUCTS
PARTICLE FORMATION
ORGANIC-COMPOUNDS
REACTION-KINETICS
VAPOR-PRESSURES
CROSS-REACTIONS
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