Formation of aqueous-phase α-hydroxyhydroperoxides (α-HHP): potential atmospheric impacts 1Department of Chemistry, University of Toronto, Toronto, ON, Canada
17 Jun 2013
2Environmental NMR Centre, University of Toronto, Toronto, ON, Canada
Received: 12 February 2013 – Published in Atmos. Chem. Phys. Discuss.: 27 February 2013 Abstract. The focus of this work is on quantifying the degree of the aqueous-phase
formation of α-hydroxyhydroperoxides (α-HHPs) via reversible
nucleophilic addition of H2O2 to aldehydes. Formation of this
class of highly oxygenated organic hydroperoxides represents a poorly
characterized aqueous-phase processing pathway that may lead to enhanced SOA
formation and aerosol toxicity. Specifically, the equilibrium constants of
α-HHP formation have been determined using proton nuclear-magnetic-resonance
(1H NMR) spectroscopy and proton-transfer-reaction mass spectrometry
(PTR-MS). Significant α-HHP formation was observed from
formaldehyde, acetaldehyde, propionaldehyde, glycolaldehyde, glyoxylic acid,
and methylglyoxal, but not from methacrolein and ketones. Low temperatures
enhanced the formation of α-HHPs but slowed their formation rates.
High inorganic salt concentrations shifted the equilibria toward the
hydrated form of the aldehydes and slightly suppressed α-HHP
formation. Using the experimental equilibrium constants, we predict the
equilibrium concentration of α-HHPs to be in the μM level in
cloud water, but it may also be present in the mM level in aerosol liquid water
(ALW), where the concentrations of H2O2 and aldehydes can be high.
Formation of α-HHPs in ALW may significantly affect the effective
Henry's law constants of H2O2 and aldehydes but may not affect
their gas-phase levels. The photochemistry and reactivity of this class of
atmospheric species have not been studied.
Revised: 12 May 2013 – Accepted: 13 May 2013 – Published: 17 June 2013
Citation: Zhao, R., Lee, A. K. Y., Soong, R., Simpson, A. J., and Abbatt, J. P. D.: Formation of aqueous-phase α-hydroxyhydroperoxides (α-HHP): potential atmospheric impacts, Atmos. Chem. Phys., 13, 5857-5872, doi:10.5194/acp-13-5857-2013, 2013.