Elucidating the critical oligomeric steps in secondary organic aerosol and brown carbon formation
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Published:2022-06-07
Issue:11
Volume:22
Page:7259-7271
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Ji YuemengORCID, Shi Qiuju, Ma Xiaohui, Gao Lei, Wang Jiaxin, Li Yixin, Gao Yanpeng, Li Guiying, Zhang RenyiORCID, An Taicheng
Abstract
Abstract. Small α-dicarbonyls represent the major
precursors of secondary organic aerosol (SOA) and brown carbon (BrC) in the
atmosphere, but the chemical mechanisms leading to their formation remain
unclear. Here we elucidate the fundamental kinetics and mechanisms for
aqueous-phase oligomerization of glyoxal (GL) using quantum chemical and
kinetic rate calculations. Our results identify several essential isomeric
processes for GL, including protonation to yield diol / tetrol and carbenium
ions, nucleophilic addition of carbenium ions to diol / tetrol as well as to
free methylamine / ammonia (MA / AM), and deprotonation to propagate oligomers
and N-heterocycles. Both protonation and nucleophilic addition occur without
activation barriers and are dominantly driven by electrostatic attraction.
Deprotonation proceeds readily via water molecules in the absence of MA / AM
but corresponds to the rate-limiting step for N-containing cationic
intermediates to yield N-heterocycles. On the other hand, the latter occurs
readily via a catalytic process by acidic anions (e.g., SO42-). A
carbenium ion-mediated reaction rate of GL is 4.62 × 10−3 s−1 under atmospheric conditions, in good agreement with the
experimental data. Our results provide essential mechanistic and kinetic
data for accurate assessment of the role of small α-dicarbonyls in
SOA and BrC formation.
Funder
Natural Science Foundation of Guangdong Province National Natural Science Foundation of China Science and Technology Planning Project of Guangdong Province
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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