Organic Peroxide and OH Formation in Aerosol and Cloud Water

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icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion Atmos. Chem. Phys. Discuss., 15, 17367–17396, 2015 www.atmos-chem-phys-discuss.net/15/17367/2015/ doi:10.5194/acpd-15-17367-2015 ACPD © Author(s) 2015. CC Attribution 3.0 License. 15, 17367–17396, 2015

This discussion paper is/has been under review for the journal Atmospheric Chemistry Organic peroxide and and Physics (ACP). Please refer to the corresponding ﬁnal paper in ACP if available. OH formation in aerosol and cloud Organic peroxide and OH formation in water aerosol and cloud water: laboratory Y. B. Lim and B. J. Turpin evidence for this aqueous chemistry Title Page

Y. B. Lim and B. J. Turpin Abstract Introduction

Department of Environmental Sciences, Rutgers University, New Brunswick, NJ 08901, USA Conclusions References

Received: 29 May 2015 – Accepted: 01 June 2015 – Published: 25 June 2015 Tables Figures Correspondence to: Y. B. Lim ([email protected]) J I Published by Copernicus Publications on behalf of the European Geosciences Union. J I

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17367 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion Abstract ACPD Aqueous chemistry in atmospheric waters (e.g., cloud droplets or wet aerosols) is well 15, 17367–17396, 2015 accepted as an atmospheric pathway to produce secondary organic aerosol (SOAaq). Water-soluble organic compounds with small carbon numbers (C2-C3) are precursors 5 for SOAaq and products include organic acids, organic sulfates, and high molecular Organic peroxide and weight compounds/oligomers. Fenton reactions and the uptake of gas-phase OH rad- OH formation in icals are considered to be the major oxidant sources for aqueous organic chemistry. aerosol and cloud However, the sources and availability of oxidants in atmospheric waters are not well water understood. The degree to which OH is produced in the aqueous phase aﬀects the 10 balance of radical and non-radical aqueous chemistry, the properties of the resulting Y. B. Lim and B. J. Turpin 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 Title Page electrospray ionization mass spectrometry (FTICR-MS). Organic peroxides are known Abstract Introduction 15 to form through gas-phase oxidation of volatile organic compounds. They contribute secondary organic aerosol (SOA) formation directly by forming peroxyhemiacetals, and Conclusions References epoxides, and indirectly by enhancing gas-phase oxidation through OH recycling. We Tables Figures provide simulation results of organic peroxide/peroxyhemiacetal formation in clouds

and wet aerosols and discuss organic peroxides as a source of condensed-phase OH J I 20 radicals and as a contributor to aqueous SOA. J I

1 Introduction Back Close Full Screen / Esc 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 Printer-friendly Version by scattering (Seinfeld and Pandis, 1998) and sometimes by absorbing solar radiation Interactive Discussion 25 (e.g., “brown carbon”) (Andreae and Gelencser, 2006; Bones et al., 2010; Zhang et al., 2011). Although the chemical and physical properties of aerosols are needed to predict 17368 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion eﬀects, the properties of SOA are poorly understood because SOA formation itself is poorly understood. Aqueous chemistry in atmospheric waters (e.g., cloud droplets or ACPD wet aerosols) is a potentially important pathway to produce SOA (SOA ; Blando and aq 15, 17367–17396, 2015 Turpin, 2000), and could be comparable in magnitude to “traditional” SOA, formed via 5 partitioning of semivolatile organic products of gas-phase oxidation (SOAgas) globally (Liu et al., 2012; Lin et al., 2012; Henze et al., 2008) and in locations where relative Organic peroxide and humidity and aerosol hygroscopicity are high (Carlton and Turpin, 2013; Carlton et al., OH formation in 2008; Fu et al., 2008; Chen et al., 2007). Because SOAaq is formed from small water- aerosol and cloud soluble precursors with high O/C ratios, it forms SOA (e.g., oligomers, organic salts) water 10 with high O/C ratios and helps to explain the highly oxygenated nature of atmospheric Y. B. Lim and B. J. Turpin organic aerosols, while SOAgas is less oxygenated (Aiken et al., 2008; Lim et al., 2010, 2013). OH radicals are important oxidants in clouds. In the high solute concentrations Title Page present in wet aerosols a more complex system of organic radical and non-radical 15 reactions occurs (Lim et al., 2010; McNeill et al., 2012; Ervens et al., 2014). Thus, an Abstract Introduction understanding of the availability of OH radicals is important to assessing the relative Conclusions References importance of radical and non-radical chemistry in aerosols. The uptake of gas-phase OH radicals into atmospheric waters (Faust and Allen, 1993) and Fenton reactions in Tables Figures the condensed/aqueous media (Arakaki and Faust, 1998) are considered the major 20 oxidant sources for aqueous organic chemistry. Oxidant sources in organic-containing J I cloud, fog and aerosol waters and oxidant reactions with dissolved organic compounds J I have been documented (Arakaki et al., 2013; Weller et al., 2014; Long et al., 2013). Depending on sources of OH radicals, aqueous oxidation reactions could exhibit a sur- Back Close

face area dependence (e.g., controlled by OH uptake), or a volume dependence (e.g., Full Screen / Esc 25 controlled by OH production through aqueous chemistry; Ervens et al., 2014). Herein, we explore the hypothesis that organic peroxides produce OH radicals within the atmo- Printer-friendly Version spheric aqueous phase; we also demonstrate the formation of organic peroxides in the aqueous phase and their contribution to condensed phase chemistry. Interactive Discussion

17369 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion Organic peroxides (herein particularly, organic hydroperoxides = ROOH) are known to play an important role in gas phase chemistry. They are commonly found in the at- ACPD mosphere with mixing ratios of 0.1–1 ppb (Lee et al., 1993; De Serves et al., 1994; 15, 17367–17396, 2015 Sauer et al., 2001; Grossmann et al., 2003; Lee et al., 2000; Guo et al., 2014). They 5 are known to form through gas-phase reactions of volatile organic compounds (VOCs) with OH radical, NO3 radical and O3 (Atkinson and Arey, 2003). While their chem- Organic peroxide and istry is not fully understood, these atmospheric organic species are “key” to peroxy OH formation in radical/NOx chemistry (Dibble, 2007; Glowacki et al., 2012), lead to photochemical aerosol and cloud smog formation, important to the HOx-NOx-O3 balance (Wennberg et al., 1998; Singh water 10 et al., 1995), contribute to O3 formation or depletion in the upper troposphere, and form SOA (Tobias and Ziemann, 2000). Organic peroxides (formed from gas-phase ozonoly- Y. B. Lim and B. J. Turpin sis of monoterpenes, e.g., α- and β-pinenes) are major constituents of SOA (Docherty et al., 2005). Monoterpenes have a global flux second only to isoprene and maybe the Title Page most efficient SOAgas precursor class (Kanakidou et al., 2005). Organic peroxides con- 15 tribute to organic aerosol by forming peroxyhemiacetal oligomers with atmospherically Abstract Introduction abundant organic carbonyls (e.g., aldehydes and ketones) via acid catalysis in aerosols Conclusions References (Tobias and Ziemann, 2000, 2002). Due to the characteristically weak O-O bonds of organic peroxides, the gas-phase decomposition of organic peroxides through photolysis Tables Figures or intermolecular radical reactions recycles OH radicals and can enhance gas-phase 20 photooxidation of atmospheric organic compounds. Recent field studies demonstrate J I that gas-phase OH recycling enhances isoprene photooxidation (Paulot et al., 2009; Taraborrelli et al., 2012). J I Organic peroxides are known to be moderately water soluble (Henry’s law constant Back Close ∼ 100–1000 Matm−1). They are present in rainwater with concentrations of 0.1–10 µM Full Screen / Esc 25 (Lind et al., 1986; Hellpointer and Gab, 1989; Liang et al., 2013), presumably by uptake from the gas phase. In this work, we show that organic peroxides are also produced Printer-friendly Version from aqueous-phase OH oxidation. We identify organic peroxide products from methylglyoxal and acid catalyzed oligomers (i.e., peroxyhemiacetals formed with methylgly- Interactive Discussion oxal) by ultra-high resolution mass spectrometry. We simulate organic peroxide and

17370 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion peroxyhemiacetal formation under atmospheric conditions and explore organic peroxide contributions to aqueous-phase OH production and to SOAaq formation. ACPD 15, 17367–17396, 2015 2 Experimental section Organic peroxide and 2.1 Cuvette chamber reactions OH formation in

5 Reactions of methylglyoxal with OH radicals in the aqueous phase were conducted in aerosol and cloud a cuvette chamber, which holds 10 cuvettes (3 mL each; Spectrocell) equidistant from water a 254 nm Hg UV lamp (Strahler). Cuvettes were immersed in a water bath to main- Y. B. Lim and B. J. Turpin tain the temperature at 25 ◦C. In each cuvette, 10 mM of methylglyoxal (Sigma-Aldrich) was dissolved in 18 MΩ Mili-Q water. OH radicals (10−13–10−12 M) were generated in

10 each cuvette by photolysis of 20 mM of H2O2 (Sigma-Aldrich) with the rate constant of Title Page −5 −1 5.58 × 10 Ms . The H2O2 photolysis rate constant was determined from H2O2 + UV control experiments conducted in the same cuvette chamber as described previously Abstract Introduction (Tan et al., 2010) and corrected for light absorption by H2O2 (Lim et al., 2013). The Conclusions References OH radical concentrations were estimated via modeling (Lim et al., 2013). It should Tables Figures 15 be noted that using 20 mM of H2O2 and the 254 nm UV lamp was not intended to simulate tropospheric photolysis, rather to provide a source of OH radicals. According J I to our previous control experiments (i.e., methylglyoxal + UV; methylglyoxal + H2O2), small amounts of pyruvic, acetic and formic acids form slowly in control experiments. J I However, dicarboxylic acids, the major products, did not form in the absence of OH Back Close 20 radicals (i.e., in control experiments; Tan et al., 2010). Photooxidation of methylglyoxal was allowed to proceed for 1 h. After being removed from the chamber, the cuvettes Full Screen / Esc were kept frozen until analysis. No catalase was added in order to preserve organic peroxide products. Printer-friendly Version

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17371 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion 2.2 Organic peroxide and peroxyhemiacetal analysis ACPD Ultra high resolution Fourier Transform Ion Cyclotron Resonance Electrospray Ioniza- tion Mass Spectrometer (FTICR-MS; Thermo-Finnigan LTQ-XL, Woods Hole Oceano- 15, 17367–17396, 2015 graphic Mass Spectrometer Facility) was used to determine the elemental composition 5 of organic products as described previously (Altieri et al., 2008; Tan et al., 2012). The Organic peroxide and ◦ capillary voltage and a capillary temperature were −30.00 V and 300 C, respectively OH formation in for negative mode analyses. Positive mode analyses were conducted with a capillary aerosol and cloud ◦ voltage of 20.00 V and a capillary temperature of 260 C. Both FTICR-MS and FTICR- water MS/MS were used to analyze organic peroxide products from aqueous photooxidation 10 of methylglyoxal and a standard solution, which was prepared by adding 10 mM of Y. B. Lim and B. J. Turpin tert-butyl hydroperoxide (Sigma-Aldrich) and 10 mM of methylglyoxal (Sigma-Aldrich). These samples were diluted 100 fold with water (by volume), and diluted again with methanol (MeOH) by 2 fold (by volume). Thus, the mobile phase consisted of 50 % wa- Title Page ter and 50 % MeOH; 0.1 % of formic acid (by volume) was also added. These diluted Abstract Introduction 15 samples were immediately introduced into the electrospray ionization source by direct infusion at 5 µLmin−1. Photooxidation products of methylglyoxal were expected in both Conclusions References negative and positive modes due to a carboxylic group (negative mode) and a hydroxyl Tables Figures group (positive mode) in their structure (Table 1), whereas tert-butyl hydroperoxide is

found only in the positive mode. J I

J I 20 3 Organic peroxide chemistry Back Close

We hypothesize that aqueous-phase OH radical reactions of methylglyoxal lead to or- Full Screen / Esc ganic peroxide formation as shown in Fig. 1. OH radical reactions are initiated by H-

atom abstraction. Subsequent O2 addition and HO2 decomposition mainly lead to the Printer-friendly Version formation of pyruvic acid and acetic acid (Lim et al., 2013). Both pyruvic and acetic acid Interactive Discussion 25 react further with OH radicals and O2, forming peroxy radicals (RO2), which undergo bimolecular RO2-RO2 reactions (Lim et al., 2013). However, substantial amounts of 17372 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion peroxy radicals could also react with HO2 forming organic peroxides (as indicated by a bold arrow) since HO2 is a common byproduct of aqueous photooxidation (Lim et al., ACPD 2010 and 2013) and is also water soluble (Henry’s law constant = 4×103 Matm−1; this 15, 17367–17396, 2015 is ∼ 100 times higher than that of OH radicals). 5 We further expect organic peroxides to form peroxyhemiacetals with aldehydes via acid catalysis in the aqueous phase (Fig. 2a), as they do in dry aerosols (Tobias and Organic peroxide and Ziemann, 2000; Docherty et al., 2005). Below we document the formation of peroxy- OH formation in hemiacetals from a commercially available organic peroxide, tert-butyl hydroperoxide aerosol and cloud and methylglyoxal in aqueous solution (Fig. 2b). Then we argue that organic peroxide water 10 products (R OOH and R OOH in Fig. 1) from the aqueous OH oxidation of methyl- 1 2 Y. B. Lim and B. J. Turpin glyoxal react further with methylglyoxal in water to produce peroxyhemiacetals. Brieﬂy, a carbonyl group (aldehyde) in methylglyoxal is protonated by H+, then a hydroper- oxyl group (-OOH) attacks a protonated carbonyl group forming peroxyhemiacetal. Title Page This peroxyhemiacetal chemistry is a well established oligomerization mechanism for 15 SOA from gas-phase ozone reactions of alkenes in smog chamber studies (Tobias and Abstract Introduction Ziemann, 2000). In Tobias and Ziemann study, organic peroxides are ﬁrst formed in Conclusions References the gas phase and become particles through gas-particle partitioning. Then organic peroxides form peroxyhemiacetals with by-product aldehydes through acid-catalyzed Tables Figures heterogeneous reactions on the particle surface. In current study, the detection of per- 20 oxyhemiacetals in our aqueous chemistry experiments (see below) provides evidence J I for organic peroxide formation through aqueous photochemistry. J I

Back Close 4 Results and discussion Full Screen / Esc 4.1 Standard solution (mixture of methylglyoxal and t-butyl hydroperoxide) Printer-friendly Version FTICR-MS and FTICR-MS/MS analyses of the aqueous mixture of methylglyoxal + Interactive Discussion 25 and t-butyl hydroperoxide show methylglyoxal (m/z 127.03666, 145.04714 and + 159.06278) and a peroxyhemiacetal (PHAstd; m/z 185.07797) in the positive 17373 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion mode (Fig. 3). In a mobile phase of 50 % MeOH and 50 % water, methylglyoxal undergoes solvation both with water (hydration) and with MeOH, and is detected ACPD as a sodium adduct (i.e., m/z+ 127.03666 = [methylglyoxal + MeOH + Na]+, + + + 15, 17367–17396, 2015 m/z 145.04714 = [methylglyoxal + H2O + MeOH + Na] , and m/z + 5 159.06278 = [methylglyoxal + 2MeOH + Na] ). Methylglyoxal solvation with MeOH was veriﬁed by FTICR-MS/MS (Fig. 4). The fragments of m/z+ 159.06278 are Organic peroxide and + + + m/z 141.05203 (H2O loss), m/z 127.03668 (MeOH loss), and m/z 95.01041 OH formation in (another MeOH loss). The ion m/z+ 95.01041 is the sodium adduct to methylglyoxal aerosol and cloud (a theoretical reading for [methylglyoxal + Na]+ is m/z+ 95.01090). A sodium adduct water + 10 is also expected for a peroxyhemiacetals, and seen in Fig. 3 as m/z 185.07797 + Y. B. Lim and B. J. Turpin (= [PHAstd + Na] ). Details of FTICR-MS readings and theoretical readings based on actual molecular/atomic masses are shown in Table 1. + The PHAstd peak, m/z 185.07802 (theoretical reading of + Title Page [PHAstd + Na] = 185.07899) was fragmented by infrared multiphoton dissocia- + + 15 tion (IRMPD). Major fragments (Fig. 5) are m/z 153.05228 (MeOH loss) and m/z Abstract Introduction 95.01041 ([methylglyoxal + Na]+). In electron impact (hard ionization), fragmentation Conclusions References of organic peroxides results in the loss of HO2 (Tobias and Ziemann, 2000; Docherty et al., 2005). However, O2 loss is expected for soft ionization, IRMPD fragmentation in Tables Figures FTICR-MS/MS (M. Soule and E. Kujawinski, personal communication, 2013). In Fig. 5, + 20 the ion m/z 81.06971 indicates the loss of O2 from t-butyl hydroperoxide. We also J I + observed the O2 loss (m/z 153.07158) from PHAstd. FTICR-MS/MS and theoretical readings are provided in Table 2. J I Note that no organic peroxide peak was observed in the standard solution (nor in Back Close methylglyoxal + OH samples). This is not surprising because (1) high temperature of ◦ Full Screen / Esc 25 the capillary in an electrospray chamber (∼ 250 C) is likely to decompose organic peroxides (M. Soule, personal communication, 2013), (2) it is diﬃcult to ionize organic Printer-friendly Version peroxides (Witkowski and Gierczak, 2013) and organic peroxides react with methylglyoxal to form peroxyhemiacetals. These peroxyhemiacetals are much more stable Interactive Discussion (lesser volatile) than organic peroxides (Tobias and Ziemann, 2000). These peroxy-

17374 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion hemiacetal peaks (and fragments) appear in FTICR-MS (and FTICR-MS/MS) analysis of standard solutions and samples (see below), providing evidence for the presence ACPD (and formation) of organic peroxides from methylglyoxal + OH. FTICR-MS/MS of per- 15, 17367–17396, 2015 oxyhemiacetal peaks show corresponding organic peroxide fragments, methylglyoxal 5 and other fragments as expected (Tobias and Ziemann, 2000; Docherty et al., 2005). Organic peroxide and 4.2 Aqueous photooxidation products of methylglyoxal OH formation in aerosol and cloud A FTICR mass spectrum of an aqueous methylglyoxal solution exposed to OH radi- water cals for 60 min is shown in Fig. 6 (negative mode). Main photooxidation products (Tan − − et al., 2012; Lim et al., 2013) are seen at m/z 87.00862 (pyruvic acid) and m/z Y. B. Lim and B. J. Turpin 10 177.04036 (2, 3-dimethyltartaric acid; structure shown in Fig. 6). This spectrum also − − provides evidence for peroxyhemiacetal formation at m/z 163.02392 (= [PHA1− H] ) − − Title Page and m/z 191.01998 (= [PHA2− H] ) since these readings are very close to the theoretical readings, m/z− 163.02405 for PHA and m/z− 191.01918 for PHA (Table 1). 1 2 Abstract Introduction Fragmentation of these peaks by FTICR-MS/MS supports their identiﬁcation as perox- − − 15 yhemiacetals. In Fig. 7a, m/z 131.01339 and m/z 131.01585 result from the losses Conclusions References of MeOH and O , respectively, from PHA , and m/z− 59.01377 results from the loss 2 1 Tables Figures of O2 from R1OOH, which is the organic peroxide constituent of PHA1. Similarly, in − − Fig. 7b, m/z 159.02946 results from the loss of O2 from PHA2, and m/z 59.01377 J I results from the loss of O2 from R2OOH, which is the organic peroxide constituent of 20 PHA2. Note, as was the case with the mixed peroxide-aldehyde standard, the organic J I peroxides themselves were not observed (see previous section). Detected and theo- Back Close retical readings are provided in Table 2. + Full Screen / Esc The FTICR-MS/MS was also conducted in the positive mode (Fig. 8) for PHA1 (m/z + 187.02069 in Fig. 8a) and PHA2 (m/z 215.01565 in Fig. 8b). The theoretical readings Printer-friendly Version 25 are 187.02186 for PHA1 and 215.01678 for PHA2 (Table 1). The methylglyoxal frag- m/z+ m/z+ ments ( 95.1041 in Fig. 8a and 95.0140 in Fig. 8b) appear. This conﬁrms Interactive Discussion that both PHA1 and PHA2 are indeed acid-catalyzed products of methylglyoxal.

17375 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion 5 Atmospheric implications ACPD Using ultra-high resolution FTICR-MS and FTICR-MS/MS, we observed the presence of peroxyhemiacetals, after aqueous photooxidation of methylglyoxal and in aqueous 15, 17367–17396, 2015 methylglyoxal-organic peroxide standard solutions. The presence of stable peroxy- 5 hemiacetals is an indicator of the existence of the less stable organic peroxides. Thus, Organic peroxide and this work provides evidence for the formation of organic peroxides through aqueous OH formation in phase OH radical oxidation of methylglyoxal. aerosol and cloud water 5.1 Organic peroxide production in clouds and wet aerosols Y. B. Lim and B. J. Turpin Below we demonstrate through chemical modeling that organic peroxides photochem- 10 ically form from organics present both in clouds and wet aerosols. We used the full kinetic model for glyoxal and methylglyoxal (Lim et al., 2013) to simulate the forma- Title Page tion of organic peroxides and peroxyhemiacetals. The following updates were made Abstract Introduction to the model: (1) the rate constant for the bimolecular reactions of RO2 and HO2 was 6 −1 −1 given as 3×10 M s (Reactions R213–R219 in Table S1 in the Supplement) based Conclusions References 6 −1 −1 15 on the rate constant for [HO + HO ] ∼ 1 × 10 M s , (2) the concentration of OH in 2 2 Tables Figures the aqueous phase was set to ∼ 10−14 (previously ∼ 10−12) according to recent esti- mations (Arakaki et al., 2013) (Fig. S1a in the Supplement), (3) the concentration of −8 J I HO2 in the aqueous phase was estimated to be ∼ 10 M maintained by the Henry’s law equilibrium; therefore, the excess HO2 produced by photooxidation in the aque- J I 20 ous phase was transported to the gas phase (Fig. S1b). All the reactions included in Back Close the model are listed in Table S1. For wet aerosol simulations, 1 M (the initial concentration) of methylglyoxal was used in the aqueous phase. Note that we do not expect Full Screen / Esc that methylglyoxal is present at 1 M in aerosols. However, water-soluble organic matter is present at 1–10 M. So this analysis treats all water-soluble organic matter as if Printer-friendly Version 25 it behaves like methylglyoxal. Under wet aerosol conditions ([methylglyoxal] = 1 M, initial Interactive Discussion −14 −8 [H2O2]initial = 0 M, [OH] ∼ 10 M, and [HO2] ∼ 10 M), ∼ 400 µM of organic peroxides during the 12 h daytime were formed through aqueous OH radical reactions (Fig. 10a). 17376 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion The model also includes the sinks of aqueous-phase organic peroxides: OH radical reactions (Reactions R220–R225), photolysis (Reaction R230), and the evaporation ACPD to the gas phase (Reaction R234) in Table S1. Note that organic peroxide (ROOH) 15, 17367–17396, 2015 formation in Fig. 10a and b does not change within the Henry’s law constant, 100 to −1 5 1000 Matm , and the evaporation rate is assumed to be a diﬀusion-controlled trans- fer coeﬃcient (Lelieveld and Crutzen, 1991; Lim et al., 2005), which is the upper limit Organic peroxide and based on the equation provided by Lelieveld and Crutzen (1991). Here, the gas-phase OH formation in [ROOH] is assumed to be 1 ppb (R234 in Table S1). In atmospheric cloud conditions aerosol and cloud −14 −8 ([methylglyoxal]initial = 10 µM, [H2O2]initial = 0 M, [OH] ∼ 10 M, and [HO2] ∼ 10 M), water 10 ∼ 0.4 µM of organic peroxide formation during the 12 h daytime is expected (Fig. 10b) while all the sinks of organic peroxides listed above are included. This concentration Y. B. Lim and B. J. Turpin of aqueous-phase photochemically produced organic peroxides is within the range of measured rainwater concentrations (0.1–10 µM) and similar to the concentration ex- Title Page pected by Henry’s law equilibrium from gas-phase organic peroxides (0.1–1 ppb). Abstract Introduction 15 5.2 Peroxyhemiacetal formation in wet aerosol Conclusions References The formation of peroxyhemiacetals competes with (1) hydration of methylglyoxal and Tables Figures (2) photolysis and OH reactions of organic peroxides (Fig. 9). Competing with methylglyoxal hydration means that only a dehydrated methylglyoxal (DeMGLY), not hy- J I drated methylglyoxal (MGLY), forms a peroxyhemiacetal (PHA) with an organic perox- 20 ide (ROOH), since the aldehyde reacts with peroxides. The dehydration equilibrium for J I ∼ methylglyoxal is included in the model (R226 in Table S1). In wet aerosols, 0.4 mM of Back Close DeMGLY out of 1 M MGLY will undergo peroxyhemiacetal formation and react with OH radicals (Reactions R227 and R228 in Table S1) at the same time (Fig. S2a). The main Full Screen / Esc sink for peroxyhemiacetals is expected to be OH reaction (no evaporation is expected). 25 The peroxyhemiacetal formation equilibrium (Reaction R229) and the OH reaction of Printer-friendly Version

peroxyhemiacetals (Reaction R231) are listed in Table S1. The modiﬁed model sim- Interactive Discussion ulates ∼ 0.4 µM of peroxyhemiacetal formation during the 12 h daytime and the minor increase during the nighttime (Fig. 10b). Under cloud conditions, peroxyhemiacetal for- 17377 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion mation is negligible (Note that the model simulates ∼ 4 × 10−15 M peroxyhemiacetal formation during the daytime from 10 µM of methylglyoxal photooxidation in Fig. 10b). ACPD 15, 17367–17396, 2015 5.3 OH recycling due to the photolysis of organic peroxides in atmospheric waters Organic peroxide and −15 5 In both cloud and wet aerosol conditions, 7.5 × 10 M of aqueous-phase OH produc- OH formation in tion is expected from the photolysis of organic peroxides ([ROOH]initial ∼ 400 µM in wet aerosol and cloud aerosols and [ROOH]initial ∼ 0.4 µM in cloud droplets) formed by aqueous photooxida- water tion during the 12 h daytime (Fig. S3) while the sink of ROOH is OH reaction. Note that ∼ 10−14 M of OH was recently estimated in atmospheric waters (Arakaki et al., 2013) Y. B. Lim and B. J. Turpin −14 −15 10 and ∼ 10 –10 M of OH was previously estimated in the core of the bulk phase (Ja- cob, 1986). Thus, the aqueous production of organic peroxides in atmospheric waters could be an important source of aqueous OH through organic peroxide photolysis. Title Page Abstract Introduction

The Supplement related to this article is available online at Conclusions References doi:10.5194/acpd-15-17367-2015-supplement. Tables Figures

15 Acknowledgements. This research has been supported in part by the National Science Foun- J I dation (grants 1 052 611) and the US Environmental Protection Agency’s Science to Achieve Results (STAR) program (grant 83 541 201). The work has not been subjected to any federal J I agency review and therefore does not necessarily reﬂect the views of the EPA or NSF; no oﬃcial Back Close endorsement should be inferred. We acknowledge Melissa C. Kido Soule, Elizabeth B. Kujaw- 20 inski and the funding sources of WHOI FT-MS Users’ Facility (National Science Foundation Full Screen / Esc OCE-0 619 608 and the Gordon and Betty Moore Foundation). We also thank Paul J. Ziemann for helpful discussions. Printer-friendly Version

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17378 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion References ACPD Aiken, A. C., DeCarlo, P. F., Kroll, J. H., Worsnop, D. R., Huffman, J. A., Docherty, K.,Ulbrich, I. M., Mohr, C., Kimmel, J. R., Sueper, D., Zhang, Q., Sun, Y., 15, 17367–17396, 2015 Trimborn, A., Northway, M., Ziemann, P. J., Canagaratna, M. R., Onasch, T. B., Alfarra, R., 5 Prevot, A. S. H., Dommen, J., Duplissy, J., Metzger, A., Baltensperger, U., and Jimenez, J. L.: O / C and OM / OC Ratios of primary, secondary, and ambient organic aerosols with high Organic peroxide and resolution time-of-flight aerosol mass spectrometry, Environ. Sci. Technol., 42, 4478–4485, OH formation in 2008. aerosol and cloud Altieri, K. E., Seitzinger, S. P., Carlton, A. G., Turpin, B. J., Klein, G. C., and Marshall, A. G.: water 10 Oligomers formed through in-cloud methylglyoxal reactions: chemical composition, properties, and mechanisms investigated by ultra-high resolution FT-ICR mass spectrometry, At- Y. B. Lim and B. J. Turpin mos. Environ., 42, 1476–1490, 2008. Andreae, M. O. and Gelencsér, A.: Black carbon or brown carbon?, The nature of light- absorbing carbonaceous aerosols, Atmos. Chem. Phys., 6, 3131–3148, doi:10.5194/acp- Title Page 15 6-3131-2006, 2006. Arakaki, T. and Faust, B. C.: Sources, sinks, and mechanisms of hydroxyl radical (OH) pho- Abstract Introduction toproduction and consumption in authentic acidic continental cloud waters from Whiteface Mountain, New York: the role of the Fe(R) (R = II, III) photochemical cycle, J. Geophys. Res., Conclusions References 103, 3487–3504, 1998. Tables Figures 20 Arakaki, T., Anastasio, C., Kuroki, Y., Nakjima, H., Okada, K., Kotani, Y., Handa, D., Azechi, S., Kimura, T., Tsuhako, A., and Miyagi, Y.: A general scavenging rate constant for reaction of hydroxyl radical with organic carbon in atmospheric waters, Environ. Sci. Technol., 47, 8196– J I 8203, 2013. J I Atkinson, R. and Arey, J.: Atmospheric degradation of volatile organic compounds, Chem. Rev., 25 103, 4605–4638, 2003. Back Close Blando, J. D. and Turpin, B. J.: Secondary organic aerosol formation in cloud and fog droplets: a literature evaluation of plausibility, Atmos. Environ., 34, 1623–1632, 2000. Full Screen / Esc Bones, D. L., Henricksen, D. K., Mang, S. A., Gonsior, M., Bateman, A. P., Nguyen, T. B., Cooper, W. J., and Nizkorodov, S. A.: Appearance of strong absorbers and fluorophores in Printer-friendly Version + 30 limonene-O3 secondary organic aerosol due to NH4 -mediated chemical aging over long time scales, J. Geophys. Res., 115, D05203, doi:10.1029/2009JD012864, 2010. Interactive Discussion

17379 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion Carlton, A. G., Turpin, B. J., Altieri, K. E., Seitizinger, S. P., Mathur, R., Roselle, S. J., and Weber, R. J.: CMAQ model performance enhanced when in-cloud secondary organic aerosol ACPD is included: comparisons of organic carbon predictions with measurements, Environ. Sci. Technol., 42, 8798–8802, 2008. 15, 17367–17396, 2015 5 Carlton, A. G. and Turpin, B. J.: Particle partitioning potential of organic compounds is highest in the Eastern US and driven by anthropogenic water, Atmos. Chem. Phys., 13, 10203–10214, doi:10.5194/acp-13-10203-2013, 2013. Organic peroxide and Chen, J., Griﬃn, R. J., Grini, A., and Tulet, P.: Modeling secondary organic aerosol forma- OH formation in tion through cloud processing of organic compounds, Atmos. Chem. Phys., 7, 5343–5355, aerosol and cloud 10 doi:10.5194/acp-7-5343-2007, 2007. water De Serves, C.: Gas phase formaldehyde and peroxide measurements in the artic atmosphere, J. Geophys. Res., 99, 5471–5483, 1994. Y. B. Lim and B. J. Turpin Dibble, T. S.: Failures and limitations of quantum chemistry for two key problems in the atmospheric chemistry of peroxy radicals, Atmos. Environ., 42, 5837–5848, 2007. 15 Docherty, K. S., Wu, W., Lim, Y. B., and Ziemann, P. J.: Contribution of organic peroxides to Title Page secondary organic aerosol formed from reactions of monoterpenes with O3, Environ. Sci. Technol., 39, 4049–4059, 2005. Abstract Introduction Ervens, B., Sorooshian, A., Lim, Y. B., and Turpin, B. J.: Key parameters controlling OH-initiated formation of secondary organoc aerosol in the aqueous phase (aqSOA), J. Geophys. Res.- Conclusions References 20 Atmos., 119, 3997–4016, 2014. Tables Figures Faust, B. C. and Allen, J. M.: Aqueous-phase photochemical formation of hydroxyl radical in authentic cloudwaters and fogwaters, Environ. Sci. Technol., 27, 1221–1224, 1993. Fu, T.-M., Jacob, D. J., Wittrock, F., Burrows, J. P.,Vrekoussis, M., and Henze, D. K.: Global bud- J I gets of atmospheric glyoxal and methylglyoxal, and implications for formation of secondary J I 25 organic aerosols, J. Geophys. Res., 113, D15303, doi:10.1029/2007JD009505, 2008. Glowacki, D. R., Lockhart, J., Blitz, M. A., Klippenstein, S. J., Piling, M. J., Robertson, S. H., Back Close and Seakins, P. W.: Interception of excited vibrational quantum states by O2 in atmospheric association reactions, Science, 337, 1066–1069, 2012. Full Screen / Esc Grossmann, D., Moortgat, G. K., Kibler, M., Schlomski, S., Bachmann, K., Alicke, B., Geyer, A., 30 Platt, U., Hammer, M.-U., and Vogel, B.: Hydrogen peroxide, organic peroxides, carbonyl Printer-friendly Version compounds and organic acids measured at pabstthum during BERLIOZ, J. Geophys. Res., 108, 8250, doi:10.1029/2001JD001096, 2003. Interactive Discussion

17380 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion Guo, J., Tilgner, A., Yeung, C., Wang, Z., Louie, P. K. K., Luk, C. W. Y., Xu, Z., Yuan, C., Gao, Y., Poon, S., Herrmann, H., Lee, S., Lam, K. S., and Wang, T.: Atmospheric peroxides ACPD in a polluted subtropical environment: seasonal variation, sources and sinks, and importance of heterogeneous processes, Environ. Sci. Technol., 48, 1443–1460, 2014. 15, 17367–17396, 2015 5 Hellpointer, E. and Gab, S.: Detection of methyl, hydroxymethyl and hydroxyethyl hydroperoxides in air and precipitation, Nature, 337, 631–634, 1989. Henze, D. K., Seinfeld, J. H., Ng, N. L., Kroll, J. H., Fu, T.-M., Jacob, D. J., and Heald, C. L.: Organic peroxide and Global modeling of secondary organic aerosol formation from aromatic hydrocarbons: high- OH formation in vs. low-yield pathways, Atmos. Chem. Phys., 8, 2405–2420, doi:10.5194/acp-8-2405-2008, aerosol and cloud 10 2008. water Jacob, D. J.: Chemistry of OH in remote clouds and its role in the production of formic acid and peroxymonosulfate, J. Geophys. Res., 91, 9807–9826, 1986. Y. B. Lim and B. J. Turpin Kanakidou, M., Seinfeld, J. H., Pandis, S. N., Barnes, I., Dentener, F. J., Facchini, M. C., Van Dingenen, R., Ervens, B., Nenes, A., Nielsen, C. J., Swietlicki, E., Putaud, J. P., Balkan- 15 ski, Y., Fuzzi, S., Horth, J., Moortgat, G. K., Winterhalter, R., Myhre, C. E. L., Tsigaridis, K., Title Page Vignati, E., Stephanou, E. G., and Wilson, J.: Organic aerosol and global climate modelling: a review, Atmos. Chem. Phys., 5, 1053–1123, doi:10.5194/acp-5-1053-2005, 2005. Abstract Introduction Lee, J. H., Leahy, D. F., Tang, I. N., and Newman, L.: Measurement and speciation of gas-phase peroxides in the atmosphere, J. Geophys. Res., 98, 2911–2915, 1993. Conclusions References 20 Lee, M., Heikes, B. G., and O’Sullivan, D. W.: Hydrogen peroxide and organic hydroperoxide in Tables Figures the troposphere: a review, Atmos. Environ., 34, 3475–3494, 2000. Lelieveld, J. and Crutzen, P. J.: The role of clouds in tropospheric photochemistry, J. Atmos. Chem., 12, 229–267, 1991. J I Liang, H., Chen, Z. M., Huang, D., Zhao, Y., and Li, Z. Y.: Impacts of aerosols on the chemistry J I 25 of atmospheric trace gases: a case study of peroxides and HO2 radicals, Atmos. Chem. Phys., 13, 11259–11276, doi:10.5194/acp-13-11259-2013, 2013. Back Close Lim, H. J., Carlton, A. G., and Turpin, B. J.: Isoprene forms secondary organic aerosol through cloud processing: model simulations, Environ. Sci. Technol., 39, 4441–4446, 2005. Full Screen / Esc Lim, Y. B., Tan, Y., Perri, M. J., Seitzinger, S. P., and Turpin, B. J.: Aqueous chemistry and its 30 role in secondary organic aerosol (SOA) formation, Atmos. Chem. Phys., 10, 10521–10539, Printer-friendly Version doi:10.5194/acp-10-10521-2010, 2010. Interactive Discussion

17381 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion Lim, Y. B., Tan, Y., and Turpin, B. J.: Chemical insights, explicit chemistry, and yields of secondary organic aerosol from OH radical oxidation of methylglyoxal and glyoxal in the aqueous ACPD phase, Atmos. Chem. Phys., 13, 8651–8667, doi:10.5194/acp-13-8651-2013, 2013. Lin, G., Penner, J. E., Sillman, S., Taraborrelli, D., and Lelieveld, J.: Global modeling of SOA 15, 17367–17396, 2015 5 formation from dicarbonyls, epoxides, organic nitrates and peroxides, Atmos. Chem. Phys., 12, 4743–4774, doi:10.5194/acp-12-4743-2012, 2012. Lind, J. A. and Kok, G.: Henry’s Law determinations for aqueous solutions of hydrogen peroxide, Organic peroxide and methylhydroperoxide, and peroxyacetic acid, J. Geophys. Res., 91, 7889–7895, 1986. OH formation in Liu, J., Horowitz, L. W., Fan, S., Carlton, A. G., and Levy II, H.: Global in-cloud production of aerosol and cloud 10 secondary organic aerosols: implementation of a detailed chemical in the GFDL Atmospheric water Model AM3, J. Geophys. Res., 117, D15303, doi:10.1029/2012JD017838, 2012. Long, Y., Charbouillot, T., Brigante, M., Maihot, G., Delort, A.-M., Chaumerliac, N., and Deguil- Y. B. Lim and B. J. Turpin laume, L.: Evaluation of modeled cloud chemistry mechanism against laboratory irradiation experiments: the HxOx/iron/carboxylic acid chemical system, Atmos. Environ., 77, 686–695, 15 2013. Title Page McNeill, V. F., Woo, J. L., Kim, D. D., Schwier, A. N., Wannell, N. J., Sumner, A. J., and Barakt, J. M.: Aqueous-phase secondary organic aerosol and organosulfate formation in Abstract Introduction atmospheric aerosols: a modeling study, Environ. Sci. Technol., 46, 8075–8081, 2012. Paulot, F., Crounse, J. D., Kjaergaard, H. G., Kurten, A., Clair, J. M. St., Seinfeld, J. H., and Conclusions References 20 Wennberg, P.O.: Unexpected epoxide formation in the gas-phase photooxidation of isoprene, Tables Figures Science, 325, 730–733, 2009. Sauer, F., Beck, J., Schuster, G., and Moortgat, G. K.: Hydrogen peroxide, organic peroxides and organic acids in a forest area during FIELDVOC’94, Chemosphere Global Change Sci., J I 3, 309–326, 2001. J I 25 Seinfeld, J. H. and Pandis, S. N.: Atmospheric Chemistry and Physics, 1st Edn., Wiley- Interscience, New York, 1998. Back Close Seinfeld, J. H. and Pankow, J. F.: Organic atmospheric particulate material, Annu. Rev. Phys. Chem., 54, 121–140, 2003. Full Screen / Esc Singh, H. B., Kanakidou, M., Crutzen, P. J., and Jacob, D. J.: High concentrations and pho- 30 tochemical fate of oxygenated hydrocarbons in the global troposphere, Nature, 2, 50–54. Printer-friendly Version 1995. Interactive Discussion

17382 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion Tan, Y., Carlton, A. G., Seitzinger, S. P., and Turpin, B. J.: SOA from methylglyoxal in clouds and wet aerosols: measurements and prediction of key products, Atmos. Environ., 44, 5218– ACPD 5226, 2010. Tan, Y., Lim, Y. B., Altieri, K. E., Seitzinger, S. P., and Turpin, B. J.: Mechanisms leading to 15, 17367–17396, 2015 5 oligomers and SOA through aqueous photooxidation: insights from OH radical oxidation of acetic acid and methylglyoxal, Atmos. Chem. Phys., 12, 801–813, doi:10.5194/acp-12-801- 2012, 2012. Organic peroxide and Taraborrelli, D., Lawrence, M. G., Crowley, J. N., Dillon, T. J., Gromov, S., Groß, C. B. M., OH formation in Vereecken, L., and Lelieveld, J.: Hydroxyl radical buffered by isoprene oxidation over tropical aerosol and cloud 10 forests, Nat. Geosci., 5, 190–193, 2012. water Tobias, H. J. and Ziemann, P. J.: Thermal desorption mass spectrometric analysis of organic aerosol formed from reactions of 1-tetradecene and O3 in the presence of alcohols and Y. B. Lim and B. J. Turpin carboyxlic acids, Environ. Sci. Technol., 34, 2105–2115, 2000. Weller, C., Tilgner, A., Brauer, P., and Herrmann, H.: Modeling the impact of iron-carboxylate 15 photochemistry on radical budget and carboxylate degradation in cloud droplet and particles, Title Page Environ. Sci. Technol., 48, 5652–5659, 2014. Wennberg, P. O., Hanisco, T. F., Jaegle, L., Jacob, D. J., Histsa, E. J., Lanzendorf, E. J., An- Abstract Introduction derson, J. G., Gao, R.-S., Kelm, E. R., Donnelly, S. G., Del Negro, L. A., Fahey, D. W., McKeen, S. A., Salawitch, R. J., Webster, C. R., May, R. D., Herman, R. L., Proffit, M. H., Conclusions References 20 Margitan, J. J., Atlas, E. L., Schauffler, S. M., Flocke, F., EmElroy, C. T., and Bui, T. P.: Hydro- Tables Figures gen radicals, nitrogen radicals, and the production of O3 in the upper troposphere, Science, 279, 49–53, 1998. Witkowski, B. and Gierczak, T.: Analysis of α-acyloxyhydroperoxy aldehydes with Electrospray J I Ionization-Tandem Mass Spectrometry (ESI-MSn), J. Mass Spectrom., 48, 79–88, 2013. J I 25 Zhang, Q., Jimenez, J. L., Canagaratna, M. R., Allan, J. D., Coe, H., Ulbrich, I., Al- farra, M. R., Takami, A., Middlebrook, A. M., Sun, Y. L., Dzepina, K., Dunlea, E., Back Close Docherty, K., DeCarlo, P. F., Salcedo, D., Onasch, T., Jayne, J. T., Miyoshi, T., Shimono, A., Hatakeyama, S., Takegawa, N., Kondo, Y., Schneider, J., Drewnick, F., Weimer, S., De- Full Screen / Esc merjian, K., Williams, P., Bower, K., Bahreini, R., Cottrell, L., Griffin, R. J., Rautiainen, J., 30 and Worsnop, D. R.: Ubiquity and dominance of oxygenated species in organic aerosols in Printer-friendly Version anthropogenically-influenced northern hemisphere mid-latitudes, Geophys. Res. Lett., 34, L13801, doi:10.1029/2007GL029979, 2007. Interactive Discussion

17383 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion Zhang, X., Lin, Y.-H., Surratt, J. D., Zotter, P.,Prevot, A. H. S., and Weber, R. J.: Light-absorbing soluble organic aerosol in Los Angeles and Atlanta: a contrast in secondary organic aerosol, ACPD Geophys. Res. Lett., 38, L21810, doi:10.1029/2011GL049385, 2011. Ziemann, P. J.: Evidence of low-volatility diacyl peroxides as a nucleating agent and major 15, 17367–17396, 2015 5 component of aerosol formed from reactions of O3 with cyclohexene and homologous compounds, J. Phys. Chem. A, 106, 4390–4402, 2002. Organic peroxide and OH formation in aerosol and cloud water

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17384 1 Table 1. FTICR-MS and theoretical readings for methylglyoxal, organic peroxides and 1 Table 1. FTICR-MS and theoretical readings for methylglyoxal, organic peroxides and 2 peroxy hemicetals. | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion 1 1 TableTable 1. 1.FTICR-MS FTICR-MS and andtheoretical theoretical readings readings for methylglyoxal,for methylglyoxal, organic organic peroxides peroxides and and 2 peroxy1 hemicetals. Table 1. FTICR-MS and theoretical readings for methylglyoxal, organic peroxides and Table 1. FTICR-MS1 MethylglyoxalTable 1. and FTICR-MS theoretical and theoretical readingsOrganic readings Peroxide for methylglyoxal,for methylglyoxal, Peroxyhemiacetal organic peroxides peroxides and and peroxy 21 2 peroxyTableperoxy hemicetals.1. hemicetals.FTICR-MS and theoretical readings for methylglyoxal,(= Methylglyoxal organic peroxides + Organic Peroxide) and ACPD hemicetals.2 2peroxy peroxy hemicetals. hemicetals. Peroxyhemiacetal 2 peroxy hemicetals.Methylglyoxal1 Table 1 1. Table FTICR-MS 1. FTICR-MS and theoretical and Organictheoretical readings readings forPeroxide methylglyoxal, for methylglyoxal, organicPeroxyhemiacetal peroxidesorganic peroxides and and MethylglyoxalMethylglyoxal OrganicOrganic Peroxide Peroxide Peroxyhemiacetal(=PeroxyhemiacetalPeroxyhemiacetal Methylglyoxal + Organic Peroxide) 15, 17367–17396, 2015 MethylglyoxalMethylglyoxalMethylglyoxal Organic OrganicOrganic Peroxide Peroxide (= Methylglyoxal(= Methylglyoxal + Peroxyhemiacetal Organic + Organic Peroxide) Peroxide) 2 peroxy2 hemicetals.peroxy hemicetals. (= Methylglyoxal(=(= MethylglyoxalMethylglyoxal + Organic + Organic Peroxide) Peroxide)Peroxide) Methylglyoxal1 Table 1. FTICR-MS andOrganic theoretical Peroxide readings for methylglyoxal,Peroxyhemiacetal organic peroxides and t-butyl hydroperoxide (= MethylglyoxalPeroxyhemiacetalPHA + Organic Peroxide) 2 peroxyMethylglyoxal hemicetals.Methylglyoxal Organic OrganicPeroxide Peroxide Peroxyhemiacetalstd MW 72.02113 MW 90.06809 (= Methylglyoxal(= MWMethylglyoxal + Organic 162.08922 Peroxide) + Organic Peroxide) Organic peroxide and

Theoretical FTICR-MS Theoreticalt-butyl t-butyl hydroperoxideFTICR-MS hydroperoxide TheoreticalPeroxyhemiacetal FTICR-MS a Methylglyoxal t-butylt-butyl t-butylhydroperoxidea hydroperoxideOrganic hydroperoxide Peroxide PHAa PHAPHA std std OH formation in Reading Reading Reading Reading Reading(= Methylglyoxal stdPHA + OrganicReadingstdPHA Peroxide)st d MW 72.02113 MW 90.06809 MW 162.08922 MWMW MW72.02113 72.02113 72.02113MW 72.02113 MW 90.06809MW MW 90.06809 90.06809 MWMW 162.08922 162.08922 MW 162.08922 MW 162.08922 MW 72.02113 t-butyl+t-butyl hydroperoxideMW hydroperoxide 90.06809t-butyl +hydroperoxide + MW PHA162.08922 + aerosol and cloud TheoreticalTheoretical TheoreticalFTICR-MS FTICR-MSFTICR-MS Theoretical [M + Theoretical Na]Theoretical = FTICR-MSm/z FTICR-MS (NotFTICR-MS Theoretical [MTheoretical + TheoreticalNa]PHA PHA=st d FTICR-MSst dFTICR-MS stdFTICR-MSm/z Theoreticala FTICR-MSa Theoreticala a FTICR-MS Theoreticala a FTICR-MS TheoreticalTheoreticala a Reading FTICR-MSFTICR-MSMW 72.02113MWReading 72.02113 TheoreticalTheoretical aa ReadingMW 90.06809 MWFTICR-MS FTICR-MS90.06809Reading TheoreticalMWReadinga 162.08922aTheoreticalMW 162.08922FTICR-MSReading FTICR-MS ReadingReadingMWReading 72.02113a Reading Reading +Reading Reading Reading113.05786ReadingMW 90.06809a ReadingDetected)Reading Reading Reading185.07899 ReadingMW 162.08922a ReadingReading185.07797Reading water Readinga Theoreticalm/zReadingTheoretical FTICR-MS FTICR-MS ReadingTheoretical Theoreticala FTICR-MSReading FTICR-MS Theoretical ReadingTheoretical FTICR-MS aFTICR-MS Reading Reading Reading a Reading+ + a + Reading+ +Reading + a + + Reading Theoretical ReadingFTICR-MS a Reading Reading Theoretical Reading[M+ Reading+[M Na] + Na] t-butyla= Reading FTICR-MS = hydroperoxide+ Readingm/z m/z (Not Reading (Not TheoreticalReading [M +[M Na] a+ Reading+ Na] = Reading = FTICR-MSm/z Reading+ m/z a 127.03666 [M + Na] =a + m/z (Not+ [M + Na] =a + PHAm/zstd + Reading Reading + Reading[M + Na]113.05786 +=+ Reading+ m/z+ Detected) (Not+ + Reading[M185.07899 + + Na] + = +Reading + 185.07797m/z+ + MW 72.02113+ [M113.05786[M + + Na] Na] [M = = +MW Na] m/z90.06809Detected) = (Notm/z m/z (Not (Not[M +185.07899 Na] [M = [M + Na] MW + Na]=m/z 162.08922 185.07797 = m/z m/z Y. B. Lim and B. J. Turpin b + m/z m/z 113.05786 Detected) 185.07899 185.07797 [M + MeOH + 113.05786+ +Detected) 185.07899 + 185.07797+ + Theoreticalm/z +127.03666FTICR-MS+ +113.05786Theoretical113.05786 Detected) FTICR-MS Detected)185.07899 Theoretical185.07899 185.07797 FTICR-MS185.07797 Na] m/z+127.03666+ m/z [M +m/z 113.05786Na]+ = m/z +(NotDetected) [M + Na]+ 185.07899= m/z + 185.07797 127.03666Reading m/z a 127.03666 Reading [M + Na] = 113.05786Readinga m/z (NotReading Detected) [M + Na]Reading= 185.07899 a m/zReading185.07797 b b m/z 127.03666 = 127.03715 [M + [MMeOH + MeOH + 127.03666 + + 127.03666 113.05786 Detected) 185.07899 185.07797 + b + m/zb b + + + + [M + MeOH + Na][M Na] + MeOH 127.03666 [M + + MeOH + [M + Na] = m/z (Not [M + Na] = m/z b + R1OOH PHA1 [M + + MeOH = + 127.03715 Na]127.03666 + Na] Na] = 127.03715b + 113.05786 Detected) 185.07899 185.07797 + = 127.03715 = 127.03715 m/z MW 92.01096 MW 164.03209 Title Page [M= 127.03715 + MeOH Na] b + R1OOH PHA 1 [M + MeOHb + + + R1OOH PHA1 [M MeOH Na] R1OOH R1OOH PHA1 PHA1 + =Na] 127.03715 + + 127.03666 Theoretical FTICR-MS Theoretical FTICR-MS Na] R1OOHMWMW 92.01096 92.01096 MWPHAMW 164.032091 164.03209 = 127.03715 b a MW 92.01096MW 92.01096 MW 164.03209a MW 164.03209 = 127.03715 [M + MeOH + ReadingTheoretical R1OOH Reading FTICR-MS ReadingTheoretical PHA ReadingFTICR-MS1 = 127.03715 + TheoreticalMW 92.01096Theoretical FTICR-MS FTICR-MS Theoretical MWTheoretical 164.03209 FTICR-MS FTICR-MS Abstract Introduction Na] + TheoreticalMW 92.01096a FTICR-MS Theoretical - FTICR-MS MWa 164.03209 - m/z ReadingMWaa 92.01096R OOHa Reading Readinga aMWa 164.03209Reading = 127.03715 Theoretical ReadingReading R1OOH ReadingFTICR-MS 1 ReadingReading ReadingTheoreticalReading[MReading - H] Reading = PHA ReadingFTICR-MS 1 ReadingReadingm/zPHA 1 ++ + - - 145.04714 +m/zm/z Theoreticalm/z a- FTICR-MS- Theoretical- a - - - FTICR-MS- - m/z Theoreticala MW 92.01096RFTICR-MSOOH [M163.02427 [M- H]Theoretical - [M =H] [M a- =-H] H] = = m/zPHA MW163.02405 m/z FTICR-MS 164.03209m/zm/z Reading Reading[M - H]MW = 92.01096Readingm/zReading1 (Not Reading ReadingMW 164.03209Reading1 Reading Conclusions References + 145.04714145.04714 - a------163.02427163.02427163.02427 + 163.02405a 163.02405 163.02405+ 145.04714 Reading[M[M - H] - H] =[M =MW - H] 92.01096m/z= Reading (Notm/z m/z (Not (Not 163.02427Reading- MW 164.03209163.02405- Reading m/z Theoretical91.00314Theoretical [M - H] = FTICR-MS Detected)m/zFTICR-MS (Not [MTheoretical[M - H]+ Na]+ = Theoretical = + FTICR-MS+m/zm/z + FTICR-MS + 91.00314a 91.00314Detected) Detected)[M + Na] [M= a+ Na]-+ =m/z m/z+ + - [M + H2O + m/z 91.00314- 91.00314Theoretical a - Detected)Detected)FTICR-MS [M +[MTheoretical Na] +- H]Na] = = = am/zFTICR-MSm/z m/z b + [M145.04714 + H2O +[M + H 2O + ReadingReading aReadingReading163.02427187.02186Reading187.02186 Reading 187.02069a 163.02405Reading187.02069 Reading [M + Hb2O + + b + [M - H] = m/z (Not 187.02186 187.02069 Tables Figures MeOH + Na][M + HMeOH2O + + Na]MeOH + + Na] Reading Reading 187.02186Reading- 187.02069Reading- b b + 145.04714 + + - - 187.02186+ 187.02069+ MeOHMeOH + Na] + Na]m/z + [M - H] = m/z (Not [M -163.02427 H] = - - m/z163.02405 - - = 145.04768 = 145.04768= m/z +145.04768 m/z91.00314 − Detected)− [M + Na][M −= - [M H] =- H]m/z = m/z− m/z [M + H O += 145.04768= 145.04768145.04714 m/z 145.04714 [M − H] =- 91.00314 m/z- (Not Detected) [M − H] = 163.02427+ m/z 163.02405+ 2 b + 145.04714 91.00314 - Detected)- 187.02186163.02427[M ++ Na] =187.02069 163.02405+m/z [M + H bO + MeOH+ + Na] 145.04714 [M - H] = [M- - H] =m/z (Notm/z - (Not [M + Na]163.02427163.02427= 187.02186 163.02405m/z 187.02069163.02405 MeOH2 + Na] [M - H] = m/z (Not + + [M + H2O + 187.02186+ 187.02069+ ==145.04768 145.04768b + 91.00314 91.00314Detected) Detected) [M + Na][M + =Na] = + m/zm/z + J I [MMeOH + H O ++ Na] [M + H O + 91.00314 Detected) PHA[M2 + Na]PHA2 = m/z 2 2 R2OOH R2OOH 187.02186187.02186 187.02069187.02069 = 145.04768b + MeOHb + Na] + PHAPHA2 2 MeOH[M + H+ 2Na]O + + + RMW2OOH 120.00588R OOH MW 192.02701PHA 2 b + m/z R2OOHMW2 120.00588 187.02186MW 192.02701 187.02069 MeOH= 145.04768 + Na] = 145.04768 m/z J I + 159.06278+ MW 120.00588 MW 192.02701 m/z +m/z 159.06278TheoreticalMW MW 120.00588Theoretical 120.00588 FTICR-MS FTICR-MS Theoretical TheoreticalMWMW 192.02701FTICR-MS FTICR-MS = 145.04768 m/z Readinga Readinga Readinga PHAReading2a R2OOHReading Reading Reading Reading 159.06278 159.06278 159.06278 Theoretical TheoreticalTheoretical FTICR-MS FTICR-MSFTICR-MS TheoreticalTheoreticalTheoretical FTICR-MSFTICR-MSFTICR-MS Back Close a - -a PHA- 2 - m/z++ 159.06278 MWReadingReading a120.00588a R2OOH ReadingReading [M -Reading H]MW Reading= [M 192.02701 a- H] = m/zPHAReading 2 Readingm/z m/zb b Reading ReadingR2OOH Reading Reading [M + 2MeOH [M ++ 2MeOH + - - - - 191.01918191.01918 PHA191.01998 2 191.01998 b + + + + [M -R H]2OOH =[M - H] m/z= (Not m/z (Not - - [M + 2MeOH + Na]Na] 159.06278= 159.06330Na] = 159.06330 + MWMW 120.00588 120.00588MW 120.00588 + MWMW MW 192.02701 + m/z Theoreticalm/z 118.99805 118.99805 FTICR-MSDetected) Detected) Theoretical[M + Na][M [M= - - + H] Na] =+ FTICR-MS =m/z m/z-m/z- + Full Screen / Esc = 159.06330 b + a [M[M - - H]H]a = m/zm/zPHA [M + 2MeOHb + Reading MW 120.00588- Reading - ReadingMW 192.02701Reading 2 [M +b 2MeOH+ + m/z159.06278 159.06278 Theoretical[MTheoretical -- H] R= 2OOH FTICR-MS -FTICR-MSm/z (Not 215.01678 191.01918TheoreticalTheoretical191.01918215.01678 215.01565 191.01998FTICR-MS215.01565 191.01998FTICR-MS [M + 2MeOH+ Na]+ = 159.06330 Theoretical[M -- H] = a FTICR-MSm/z- (Not Theoreticala FTICR-MS + Na] = 159.06330 [M - H] = a m/z (Not 191.01918 +a 191.01998+ Na] = 159.06330 159.06278 Theoreticala 118.99805 ReadingFTICR-MS Detected)Reading Theoretical[MReading +a +Na] = FTICR-MSReading+m/z a + ReadingReading118.99805MW 120.00588ReadingDetected)Reading [M Reading +Reading -Na]+ = MWm/zReading -192.02701Reading + 3 Theoretical3 aTheoretical readingm/z is readingbased 118.99805on is actual based atomic/molecularona actual atomic/molecularDetected) weights obtained weights[M by[M obtained -online H]+ Na] = software,by a online= software,m/zm/z b Reading− Reading− Reading215.01678215.01678− - 215.01565Reading215.01565− - Printer-friendly Version [M + 2MeOH4 + “Molecular Isotopic Distribution[M − AnalysisH] - = 118.99805 (MIDAs)” m/z- (Not Detected) [M − H][M= - 191.01918H]- = m/zm/z191.01998 - + 4 159.06278“Molecularb Isotopic [M Distribution - H] = Analysism/z (MIDAs)” (Not 191.01918215.01678+ 191.01998215.01565+ Na] = 159.06330 [M + 2MeOH + Theoretical - FTICR-MS- [M +[MNa]191.01918 -Theoretical =H]215.01678 = 191.01998m/z m/z215.01565FTICR-MS 5 a b(http://www.ncbi.nlm.nih.gov/CBBresearch/Yu/midas/index.html).5+ (http://www.ncbi.nlm.nih.gov/CBBresearch/Yu/midas/index.html).[M - aH] = m/z (Not + - a + - [M + 2MeOHa b +Na] = 159.06330b 118.99805 - Detected) - [M[M + Na] - H] = = + m/zm/z + a 3 TheoreticalMeOH = Methanol. reading isNote based that onthe actualmobileReading atomic/molecularphase cont ains 50% Readingwaterweights (with obtained 0.05% 191.01918 formic by onlineReading acid) andsoftware, 191.01998 Reading Theoretical3 + readingTheoretical6 b is based on6 reading actual MeOH atomic/molecular is =based Methanol. on weights actual Note obtained[M thatatomic/molecular - byH] the online118.99805 mobile= software, phase “Molecular m/zweights contains Detected) Isotopic(Not 50%obtained Distribution water by (with Analysis [Monline 0.05% + (MIDAs)” Na] software, formic = acid) andm/z Interactive Discussion a[MNa] + 2MeOH = 159.06330 + - - 215.01678191.01918 + 215.01565191.01998 + 3 (http://Theoreticalwww.ncbi.nlm.nih.gov/CBBresearch/Yu/midas/index.html+4 4 “Molecular 7 “Molecularreading50%7 MeOH.Isotopic is50% basedIsotopic MeOH.Distribution on Distribution actual [M ).Analysis atomic/molecular - AnalysisH] = (MIDAs)” (MIDAs)”m/z weights (Not obtained by online215.01678 software, 215.01565 b Na] = 159.06330 c 118.99805 Detected) [M + Na] = m/z MeOH = Methanol. 8 NoteMeO that the is mobile a cdeprotonated phase contains MeOH. 50 % water (with 0.05 % formic acid) and 50 % MeOH. + - + - c 5 (http://www.ncbi.nlm.nih.gov/CBBresearch/Yu/midas/index.html).8 MeO is a deprotonated MeOH. 4 “MolecularMeO5 is a deprotonated (http://www.ncbi.nlm.nih.gov/CBBresearch/Yu/midas/index.html). Isotopic MeOH. Distribution Analysis118.99805 (MIDAs)” Detected) [M + 215.01678Na] [M= - H] =m/z 215.01565 m/z a bb 3 Theoretical[M 6+ 2MeOH 6b MeOH 3reading MeOH + =aTheoretical Methanol. is = basedMethanol. reading Noteon actual Note that is based thethat atomic/molecular mobile the on mobileactual phase atomic/molecular phase- cont weights ainscont ains50% obtained 50% waterweights- water (with obtainedby215.01678 (with online0.05% 0.05% by software,formic online formic software,acid) 215.01565 acid) and and 5 (http://www.ncbi.nlm.nih.gov/CBBresearch/Yu/midas/index.html).+ 9 9 [M - H] = m/z (Not 191.01918 191.01998 bNa] = 159.06330 7 50% MeOH. 46 “MolecularMeOHa 7 =50% Methanol.Isotopic4 cMeOH.“Molecular Distribution Note Isotopicthat theAnalysis Distribution mobile (MIDAs)” phase Analysis cont (MIDAs)”ains 50% water (with 0.05% formic acid)+ and + 3 Theoretical8c MeO reading is a deprotonated is based on MeOH. actual 118.99805atomic/molecular17385 weightsDetected) obtained by online[M + Na]software, = m/z 5 (http://www.ncbi.nlm.nih.gov/CBBresearch/Yu/midas/index.html).a 8 MeO5 is (http://www.ncbi.nlm.nih.gov/CBBresearch/Yu/midas/index.html).a deprotonated MeOH. 73 50%Theoretical MeOH. reading b is based on actual atomic/molecular weights obtained by online software, 4 b c “Molecular 6 IsotopicMeOH =Distribution Methanol. Note Analysis that the mobile(MIDAs)” phase contains 50% water (with 0.05%215.01678 formic acid) and 215.01565 684 MeOH“MolecularMeO is = aMethanol. deprotonated Isotopic Note Distribution MeOH. that the mobileAnalysis phase (MIDAs)” contains 50% water (with 0.05% formic acid) and17 17 5 (http://www.ncbi.nlm.nih.gov/CBBresearch/Yu/midas/index.html).9 9 7 50% MeOH. 75 50%(http://www.ncbi.nlm.nih.gov/CBBresearch/Yu/midas/index.html).b MeOH. c 6 c MeOH =8 Methanol.MeO is aNote deprotonated that the MeOH. mobile phase contains 50% water (with 0.05% formic acid) and 389 aMeO bTheoretical is a deprotonated reading MeOH.is based on actual atomic/molecular weights obtained by online software, 6 7 MeOH50% MeOH.= Methanol. Note that the mobile phase contains 50% water (with 0.05% formic acid) and 9 47 “Molecular50%c MeOH. Isotopic Distribution Analysis (MIDAs)” 17 17 9 8 c MeO is a deprotonated MeOH. 58 (http://www.ncbi.nlm.nih.gov/CBBresearch/Yu/midas/index.html).MeO is a deprotonated MeOH. 6 9 b MeOH = Methanol. Note that the mobile phase contains 50% water (with 0.05% formic acid)17 and 9 17 7 50% MeOH. 17 8 cMeO is a deprotonated MeOH. 17 17 9

1 Table 2. FTICR-MS/MS1 Table and 2. th FTICR-MS/MSeoretical readings and for th eoreticalfragments readings of peroxyhemiacetals for fragments andof peroxyhemiacetals and 2 organic peroxides2 organic peroxides 1 Table 2. FTICR-MS/MS and theoretical readings for fragments of peroxyhemiacetals and Organic peroxide and Table2 organic 2. peroxidesOrganicFTICR-MS/MS Peroxide 1 OrganicTable and 2. theoreticalPeroxide FTICR-MS/MS andPeroxyhemiacetal readings theoretical readings for for fragments Peroxyhemiacetalfragments of peroxyhemiacetals of peroxyhemiacetals and and or- ganic1 Table peroxides. 2. OrganicFTICR-MS/MS Peroxide and 2th eoreticalorganic readings peroxides for fragmPeroxyhemiacetalents of peroxyhemiacetals and OH formation in 2 organic peroxides 1 Table 2. FTICR-MS/MS and theoretical readings for fragments of peroxyhemiacetals and 2 organicOrganic peroxides Peroxide Peroxyhemiacetal aerosol and cloud Organic Peroxide Peroxyhemiacetal Organic Peroxide Organic Peroxide PeroxyhemiacetalPeroxyhemiacetal t-butyl hydroperoxide t-butyl hydroperoxide PHA water t-butyl hydroperoxide PHAstd std PHAstd t-butyl hydroperoxide PHAstd Fragment (loss of O2) Fragment (lossFragment of O2) (loss of O2) Fragment Fragment (loss (loss of O of2) MeOH) Fragment (loss of MeOH) Fragmentt-butyl hydroperoxide (loss of O2) Fragmentt-butyl (loss hydroperoxide of O2) Fragment (loss of MeOH) PHAstd PHAstd Y. B. Lim and B. J. Turpin Fragment (lossFTICR- of OFTICR-2) FragmentFTICR- (lossFTICR- of OFTICR-2) Fragment (loss of MeOH)FTICR- TheoreticalTheoretical FTICR-MS/MSFTICR-MS/MSTheoretical Theoretical TheoreticalFTICR-MS/MSFragment (loss of O 2)Theoretical TheoreticalTheoretical Fragment (loss of O2) FragmentTheoretical (loss of MeOH) FragmentFragment (loss(loss of of O O22) )Fragment (lossMS/MS of FragmentO2)MS/MS Fragment (loss of O(loss2) ofMS/MS MeOH)MS/MSFTICR- MS/MS FragmentFTICR-MS/MS (loss of MeOH) ReadingReading ReadingReadingReading TheoreticalReadingReading Reading FTICR-MS/MS Reading ReadingTheoretical Reading FTICR- TheoreticalReading FTICR- TheoreticalReading FTICR-MS/MSReading TheoreticalReading ReadingMS/MS Reading Theoretical MS/MSReading Theoretical FTICR-MS/MSReading Theoretical FTICR-Reading Reading FTICR-MS/MSFTICR- MS/MS TheoreticalReading MS/MS FTICR-MS/MS Theoretical+ FTICR-MS/MS+ Theoretical[M + NaReading – + ReadingTheoretical[M + Na – Reading + Reading Reading Reading Reading[M + Na – O2+] = Readingm/z + + [M Reading+ + Na – MS/MSm/z+ + [M ++ Na Reading[M – + NaMS/MSm/z – Reading+ Reading+ [M + Na – Reading + Reading [M + NaReading – O2] = [MReading m/z+ Na – O2] Reading=O 2] = ++ m/z m/z+ MeOH]Reading[M += + Na – + m/z + m/z [M + Na –+ +m/z 81.06803 81.06971 [M + Na – O2]] == 153.07158+ m/z + O ] MeOH] =[M + + Na153.05228 – = m/z [MMeOH] + Na +– = m/z + + 153.089162 Reading+ 153.052772 O ] =+ Reading + MeOH] = + + + 81.06803 81.0697181.06803 [M + Na –81.06971 O2] = 153.07158 m/z 2 + 153.07158153.07158m/z153.05228 + 153.05228m/z153.05228 Title Page [M + Na − O2] = 81.06803+ m/z+ 81.0697181.06803[M +[M Na+ – Na − O2] 81.06971+= 153.08916 [M153.08916 + Na –m/z O 2] =153.07158 + [M +MeOH]Na153.05277− MeOH] = = 153.05277 m/z 153.05228 [M + Na – O ] = m/z 153.0891681.06803 m/z 81.06971 153.08916153.05277 m/z 153.07158 153.05277 153.05228 2 O ]+ = MeOH]+ = 153.08916 153.05277 2 153.07158 153.05228 81.06803 81.06971 153.08916 153.05277 Abstract Introduction

R1OOH PHA 1 R1OOHR1 OOH PHAPHA11 FragmentR1OOH (loss of O ) RFragment1OOH (loss of O ) FragmentPHA 1 (loss of MeOH) PHA1 2 Fragment (loss2 of O ) Fragment (loss of O ) Fragment (loss of MeOH) Conclusions References R1OOH Fragment (loss of O2PHA) 2 1 Fragment (loss of O22) Fragment (loss of MeOH) Fragment (loss of O2)Fragment (loss of O FTICR-) Fragment (lossFragment of O2) FTICR-(loss ofFTICR- O ) Fragment Fragment(lossFTICR- of MeOH) (loss of MeOH) TheoreticalFragment (lossFTICR-MS/MS of O2) TheoreticalTheoreticalFragment 2 (lossFTICR-MS/MS of OTheoretical2) FragmentTheoretical (lossFTICR- of2 MeOH)Theoretical FTICR- Fragment (loss of O2) TheoreticalFragment (lossMS/MS FTICR-MS/MSof O2) Fragment Theoretical (loss ofMS/MS MeOH) MS/MS Theoretical MS/MS Reading Reading ReadingReading ReadingReading Reading MS/MS Reading MS/MS Theoretical FTICR-MS/MSReading Theoretical ReadingReadingFTICR- Reading FTICR-MS/MSReading FTICR-Reading FTICR- TheoreticalReading ReadingFTICR- FTICR-MS/MS Tables Figures Theoretical FTICR-MS/MSTheoretical TheoreticalFTICR-MS/MSFTICR- TheoreticalTheoretical FTICR- Reading Theoretical Reading ReadingTheoretical- FTICR-MS/MS Reading- Theoretical Reading- - - Theoretical-[M – H – Reading - - - Reading[M – H – - Reading [M – H – O2] = MS/MSm/z [M – H – Om/z2] MS/MS m/zMS/MS - m/z MS/MS [MReading – H – O 2] = Readingm/zReading [M – HReading – O2-] Reading MS/MSm/z - Reading- Reading MS/MS- - MeOH][MReading – H = – - Reading− Reading− [M –Reading H – O59.013312] = − m/z59.01377 MeOH]Reading [M = –= H131.03444 –− O2] 131.01589m/z - 131.01339− m/z − 59.01331 59.01377m/z = 131.03444 131.01589ReadingReading m/z 131.01339ReadingReading Reading 130.99805MeOH] = Reading m/z [M − H − O2] = 59.01331 59.0137759.01331 [M − H − O2] =59.01377131.03444 130.99805= 131.03444 131.01589 131.01589 [M − H − MeOH] 131.01339= 130.99805 131.01339 ------[M – H – [M –- H – - - - 130.99805[M – H – - [M[M – H– H – –O O]] == [Mm/zm/z – H – O ] [M = –[M H –– O H] – Om/z] m/z m/z [M – H- – O ] m/z m/z m/z m/z 22 2 2 2 MeOH] =MeOH] 2 - = MeOH]- = J I 59.01331 59.01377 = 131.03444= 131.03444 131.01589 131.01589 = 131.03444 131.01339131.01589 131.01339 131.01339 59.01331 59.0137759.01331 59.01377 130.99805130.99805 130.99805

PHA2 R2OOH PHA2 R2OOH PHA2 J I FragmentR2OOH (loss of O2) Fragment (loss of O2) Fragment (loss of MeOH)

Fragment (loss of O2) Fragment (loss of O2) Fragment (loss of MeOH)FTICR- FTICR- Fragment (loss of O2)FragmentTheoretical (loss of Fragment OFTICR-MS/MS2PHA) 2 (loss ofFragmentTheoretical O2) (loss of O2) TheoreticalFragment (loss Fragment of MeOH) (loss of MeOH) R2OOH MS/MS MS/MS Back Close Theoretical FTICR-MS/MS TheoreticalReading Reading FTICR-MS/MSReading TheoreticalReading FTICR-MS/MS R OOH R OOH FTICR- PHA2 FTICR-FTICR-ReadingPHA 2 ReadingFTICR- ReadingTheoretical 2 FTICR-MS/MS Reading TheoreticalTheoretical2 Reading FTICR-MS/MSTheoretical Theoretical Reading ReadingTheoretical Reading Fragment (loss of O2) Fragment (loss- MS/MS of O2) Fragment- (loss ofMS/MS MeOH)- MS/MS - [M – H – MS/MS- Reading Reading ReadingReading[M – H – O2] = Readingm/z Reading Reading [M – H – O2] m/z Reading- m/z (Not Reading Readinge MeOH] = Fragment− (loss of O )− Fragment (lossFragment87.00822 of O ) (loss− of87.00832 O ) Fragmente Fragment= 159.02935− (loss (loss ofReading159.02946 O of) MeOH) Fragment (loss−Detected)Reading of MeOH) − [M − H − O2] = 87.00822 m/z2 87.00832 [M − H − O2FTICR-2] = 159.029352 m/z FTICR-159.029462 [M −159.00079H − MeOH] = 159.00079 m/z (Not Detected) Full Screen / Esc Theoretical- FTICR-MS/MS- Theoretical- - - - Theoretical[M – H – - - - [M – H – - [M – H – O2] = m/z [M[M – H– H– –O O2]2 ]= MS/MSm/z m/z [M- – H – Om/zMS/MS2] (Not m/z - m/z (Not Reading Reading Reading e FTICR-MeOH]Reading = e FTICR-MeOH] = 87.00822 87.00832 3 = 159.02935 159.02946Reading = 159.02935ReadingDetected) FTICR-159.02946 Detected)FTICR- Theoretical FTICR-MS/MSTheoretical 87.00822TheoreticalFTICR-MS/MS 87.00832 159.00079TheoreticalTheoretical Theoretical159.00079 - - - - MS/MS[M – H – - MS/MSMS/MS MS/MS [MReading – H – O 2] = Readingm/zReading [M – HReading – O2] Reading m/z Reading- Reading m/z (Not Reading 3 e ReadingMeOH] = Reading 87.00822 87.008323 = 159.02935 159.02946 Detected)Reading Reading Printer-friendly Version - - - - 159.00079 [M – H – [M – H – [M – H – O ] = [Mm/z – H – O ] = [M – H – Om/z]- m/z- [M – H – O ]- m/z-m/z - (Not m/z- (Not 2 2 2 MeOH]2 - = MeOH]- = 3 87.00822 87.0083287.00822 = 159.0293587.00832e 159.02946 = 159.02935e 159.02946Detected) Detected) 159.00079 159.00079 Interactive Discussion 3 3

17386 18

18 18

Organic peroxide and OH formation in aerosol and cloud water

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Figure 1. Organic peroxide formation from aqueous-phase OH radical reactions of methylgly- Full Screen / Esc oxal.

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Figure 2. Acid-catalyzed peroxyhemiacetal formation from a precursor, methylglyoxal with or- J I ganic peroxide products of aqueous photooxidation (a) and from methylglyoxal with tert-butyl hydroperoxide in standard solutions (b). J I Back Close

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Figure 3. A full FTICR-MS spectrum for the standard solution of methylglyoxal (10 mM) and Full Screen / Esc tert-butyl hydroperoxide (10 mM) in the positive mode.

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Figure 4. FTICR-MS/MS for m/z+ 159 (methylglyoxal). Full Screen / Esc

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+ Full Screen / Esc Figure 5. FTICR-MS/MS for m/z 185 (PHAstd).

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Back Close Figure 6. A full FTICR-MS spectrum for products of 1 h aqueous photooxidation of methylglyoxal in the negative mode. Full Screen / Esc

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− − Interactive Discussion Figure 7. FTICR-MS/MS for m/z 163 for PHA1 (a) and m/z 191 PHA2 (b).

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+ + Interactive Discussion Figure 8. FTICR-MS/MS for m/z 187 for PHA1 (a) and m/z 215 for PHA2 (b).

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Figure 9. Peroxyhemiacetal formation. J I Back Close

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Printer-friendly Version Figure 10. The atmospheric simulated concentrations of ROOH (organic peroxides) and PHA Interactive Discussion (peroxyhemiacetals) in wet aerosols (a) and cloud droplets (b) during 24 h. The ﬁrst 12 h are daytime. 17396