Production of Singlet Oxygen (1O2) during the Photochemistry of Aqueous Pyruvic Acid: The Effects of pH and Photon Flux under Steady-State O2(aq) Concentration

Alexis J. Eugene; Marcelo I. Guzman

doi:10.1021/acs.est.9b03742

Production of Singlet Oxygen (¹O₂) during the Photochemistry of Aqueous Pyruvic Acid: The Effects of pH and Photon Flux under Steady-State O₂(aq) Concentration

Alexis J. Eugene, Marcelo I. Guzman

Research output: Contribution to journal › Article › peer-review

18 Scopus citations

Abstract

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.

Original language	English
Pages (from-to)	12425-12432
Number of pages	8
Journal	Environmental Science and Technology
Volume	53
Issue number	21
DOIs	https://doi.org/10.1021/acs.est.9b03742
State	Published - Nov 5 2019

Bibliographical note

Funding 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.

Publisher Copyright:
Copyright © 2019 American Chemical Society.

ASJC Scopus subject areas

Chemistry (all)
Environmental Chemistry

Access to Document

10.1021/acs.est.9b03742

Cite this

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title = "Production of Singlet Oxygen (1O2) during the Photochemistry of Aqueous Pyruvic Acid: The Effects of pH and Photon Flux under Steady-State O2(aq) Concentration",

abstract = "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.",

author = "Eugene, {Alexis J.} and Guzman, {Marcelo I.}",

note = "Funding 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. Publisher Copyright: Copyright {\textcopyright} 2019 American Chemical Society.",

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AU - Guzman, Marcelo I.

N1 - Funding 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. Publisher Copyright: Copyright © 2019 American Chemical Society.

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N2 - 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.

AB - 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.

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