The photochemistry of pyruvic acid (PA) in aqueous atmospheric particles contributes to the production of secondary organic aerosols. This work investigates the fate of ketyl and acetyl radicals produced during the photolysis (λ ≥ 305 nm) of 5-100 mM PA under steady state [O2(aq)] = 260 μM (1.0 ≤ pH ≤ 4.5) for photon fluxes between 1 and 10 suns. The radicals diffuse quickly into the water/air interface of microbubbles and react with dissolved O2 to produce singlet oxygen (1O2∗). Furfuryl alcohol is used to trap and bracket the steady-state production of 2 × 10-12 ≤ [1O2∗] ≤ 1 × 10-11 M. Ion chromatography mass spectrometry shows that 2,3-dimethyltartaric acid (DMTA), 2-(3-oxobutan-2-yloxy)-2-hydroxypropanoic acid (oxo-C7 product), and 2-(1-carboxy-1-hydroxyethoxy)-2-methyl-3-oxobutanoic acid (oxo-C8 product) are formed under all conditions investigated. The sigmoidal dependence of initial reaction rates with pH resembles the dissociation curve of PA. For increasing photon fluxes, the branching ratio of products shifts away from the radical recombination that favors DMTA toward multistep radical chemistry forming more complex oxocarboxylic acids (oxo-C7 + oxo-C8). The large steady-state production of 1O2 indicates that PA in aerosols can be a significant source of atmospheric oxidants on par with natural organic matter.
|Number of pages||8|
|Journal||Environmental Science and Technology|
|State||Published - Nov 5 2019|
Bibliographical noteFunding Information:
M.I.G. thanks the U.S.A. National Science Foundation for research funding under awards 1903744 and 1255290. A.J.E. acknowledges support by the NASA Earth and Space Science Fellowship (NESSF) Program.
Copyright © 2019 American Chemical Society.
ASJC Scopus subject areas
- Chemistry (all)
- Environmental Chemistry