Abstract
Abstract. Aqueous chemistry in atmospheric waters (e.g., cloud droplets or wet aerosols) is considered a potentially important atmospheric pathway to produce secondary organic aerosol (SOAaq). Water-soluble organic compounds with small carbon numbers (C2–C3) are precursors for SOAaq; products include organic acids, organic sulfates, and high-molecular-weight compounds/oligomers. Fenton reactions and the uptake of gas-phase OH radicals are considered to be the major oxidant sources for aqueous organic chemistry. However, the sources and availability of oxidants in atmospheric waters are not well understood. The degree to which OH is produced in the aqueous phase affects the balance of radical and non-radical aqueous chemistry, the properties of the resulting aerosol, and likely its atmospheric behavior. This paper demonstrates organic peroxide formation during aqueous photooxidation of methylglyoxal using ultra-high-resolution Fourier transform ion cyclotron resonance electrospray ionization mass spectrometry (FTICR-MS). Organic peroxides are known to form through gas-phase oxidation of volatile organic compounds. They contribute secondary organic aerosol (SOA) formation directly by forming peroxyhemiacetals and epoxides (i.e., IEPOX), and indirectly by enhancing gas-phase oxidation through OH recycling. We provide simulation results of organic peroxide/peroxyhemiacetal formation in clouds and wet aerosols and discuss organic peroxides as a source of condensed-phase OH radicals and as a contributor to aqueous SOA.
Highlights
Secondary organic aerosol (SOA) is a major component of atmospheric fine particulate matter (PM2.5) (Zhang et al, 2007), contributes to adverse health, and affects climate by scattering (Seinfeld and Pandis, 1998) and sometimes by absorbing solar radiation (e.g., “brown carbon”) (Andreae and Gelencser, 2006; Bones et al, 2010; Zhang et al, 2011)
We provide simulation results of organic peroxide/peroxyhemiacetal formation in clouds and wet aerosols and discuss organic peroxides as a source of condensedphase OH radicals and as a contributor to aqueous secondary organic aerosol (SOA)
Because SOAaq is formed from small water-soluble precursors with high O / C ratios, it forms SOA with high O / C ratios and may explain the highly oxygenated nature of atmospheric organic aerosols, while semivolatile organic products of gas-phase oxidation (SOAgas) is less oxygenated (Aiken et al, 2008; Lim et al, 2010, 2013)
Summary
Secondary organic aerosol (SOA) is a major component of atmospheric fine particulate matter (PM2.5) (Zhang et al, 2007), contributes to adverse health, and affects climate by scattering (Seinfeld and Pandis, 1998) and sometimes by absorbing solar radiation (e.g., “brown carbon”) (Andreae and Gelencser, 2006; Bones et al, 2010; Zhang et al, 2011). Organic peroxides ( organic hydroperoxides – ROOH) are known to play an important role in gas-phase chemistry They are commonly found in the atmosphere with mixing ratios of 0.1–1 ppb (Lee et al, 1993, 2000; De Serves et al, 1994; Sauer et al, 2001; Grossmann et al, 2003; Guo et al, 2014). They are known to form through gas-phase reactions of volatile organic compounds (VOCs) with OH radicals, NO3 radicals and O3 (Atkinson and Arey, 2003) While their chemistry is not fully understood, these atmospheric organic species are “key” to peroxy radical/NOx chemistry (Dibble, 2007; Glowacki et al, 2012), lead to photochemical smog formation, are important to the HOx–NOx–O3 balance (Wennberg et al, 1998; Singh et al, 1995), contribute to O3 formation or depletion in the upper troposphere, and form SOA (Tobias and Ziemann, 2000; Ehn et al, 2014). We simulate organic peroxide and peroxyhemiacetal formation under atmospheric conditions and explore organic peroxide contributions to aqueousphase OH production and to SOAaq formation
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