1. Labile Peroxides in Secondary Organic Aerosol
Manuel Krapf, Imad El Haddad, Emily A. Bruns, Ugo Molteni, Kaspar R. Daellenbach, André S.H. Prévôt, Urs Baltensperger, Josef Dommen 
Chem 
Volume 1, Issue 4, Pages (October 2016)
DOI: /j.chempr
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2. Chem 2016 1, DOI: ( /j.chempr )
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3. Figure 1
Evolution of SOA and Total Peroxide Content during Ozonolysis of α-Pinene in the Presence of an OH Scavenger
Trace symbols (open and closed circles, diamonds, and squares) in (A) and (B) represent the indicated experiments (E1–E5). Dark ozonolysis (gray shaded areas) starts at t = 0. White shaded areas represent times with UV lights on. Experiment 1 (E1; green and blue circles in A and B, respectively) is an ozonolysis experiment without illumination. SOA mass loadings were measured with an AMS and not corrected for particle wall losses. Time traces are represented as 5 min averages. Vertical gray lines represent UV illumination for different experiments, whereas each illumination is followed by a more rapid decrease in the corresponding SOA mass as a result of SOA photolysis with JSOA = (3.3 ± 0.5) × 10−4 s−1. In (B), symbols represent measured peroxide molalities (bOOH), including measurement uncertainty. Molality is plotted at the time when the iodometric reaction in the test tube finished (40 min after start of the extraction and reaction). Therefore, the gray shaded area is shifted to clarify which filters were sampled in the dark. Best fits (exponential) are represented as open symbols. Fits are extrapolated to 1 hr after α-pinene injection. See also Figures S1 and S2.
Chem 2016 1, DOI: ( /j.chempr )
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4. Figure 2
SOA Mass Loadings, AMS Mass Fractions and Peroxide Yields from α-Pinene Ozonolysis with and without OH Scavenger
Experimental observations during dark ozonolysis (gray shaded areas) of α-pinene with (A and B) and without (C and D) an OH radical scavenger. The UV lights were switched on after the decay of labile peroxides (white areas). In (A), the solid green line (E3, Table S1) represents the non-wall-loss-corrected time trace of SOA mass loading. The expected curvature of SOAs without UV irradiation is represented by the dashed green line. The dashed line (E1) and open circles (E3) represent mass fraction 43 (black, predominantly CH3CO+) and mass fraction 44 (purple, mostly CO2+) without and with UV lights, respectively. In (B), the wall-loss-corrected molar yield of peroxy groups (OOH) is represented as light-blue filled circles for the experiment without UV radiation and dark-blue open symbols for those with UV illumination, which is indicated by the vertical lines for different experiments. Data were calculated on the basis of the fits in Figure 1. In (C), the solid green line (experiment 6) represents the non-wall-loss-corrected time trace of SOA. The expected curvature of SOA without UV irradiation is represented by the dashed green line. In (D), the calculated molar yield of peroxy groups is represented for experiments without OH scavenger. The vertical gray lines indicate the start of illumination. All time traces are represented as 5 min averages. See also Figures S1 and S2.
Chem 2016 1, DOI: ( /j.chempr )
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5. Figure 3 Simplified Schematic of the Hybrid 3D-VBS Framework
(A) The chemical characteristics of the OOH-containing HOMs among the first-generation products of α-pinene ozonolysis were determined by CI-APi-TOF measurements from flow-tube experiments. Color coding represents the O:C ratios of the HOMs. The functional groups were determined via analysis of the O:C and H:C ratios of the HOMs. The aggregate of the first-generation products containing one or more OOH functional groups is referred to as ROOH1.
(B) The volatility distribution and OOH content of these compounds is presented. All ROOH1 products with a log(C*) < −9 are included in the log(C*) = −9 bin. The number of α-pinene building blocks per molecule is indicated by the contour lines. The gray contour line represents monomers, and the black contour line shows dimers observed during the α-pinene ozonolysis reaction at different volatility bins. Color coding indicates the molar yield of the compounds.
(C) We consider seven surrogate compounds per chemical family, with log(C*) ranging between −2 and 4, whereas all compounds with log(C*) < −2 (mostly ROOH1) are included in the log(C*) < −2 bin. Each surrogate is characterized by a production rate, a molar yield, and intrinsic chemical characteristics, including the molecular weight and carbon, hydrogen, and oxygen numbers. Surrogates are distinguished in different chemical families according to the chemical process by which they are produced and according to whether they contain OOH moieties (ROOH) or not (NROOH). We differentiate the first-generation products (NROOH and ROOH1) from α-pinene ozonolysis and the ROOH1 degradation products (ROOH2). Each of the aforementioned products can photolyze with UV light and in the presence of an OH scavenger. In the absence of an OH scavenger, first-generation products and photolysis products may additionally react with OH. The model accounts for the possibility that each reaction yields a new family. Color coding reveals the O:C ratios of the HOMs.
See also Figure S6.
Chem 2016 1, DOI: ( /j.chempr )
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6. Figure 4 Comparison of Model Simulations with Measurements
Comparison of modeled output and observed results as a function of time with OH scavenger for chamber experiments E5, E4, and E3 (left to right). The pink vertical lines represent the times when UV irradiation was initiated. Vertical panels (A–C) correspond to the same experiment. In (A), the different color-shaded areas represent the modeled chemical families, each consisting of seven surrogates (for details, see the Figure 3 legend and the main text). The experimentally determined SOA mass (corrected for wall losses) is shown as open black circles. In (B), the measured and modeled organic mass yields are expressed by the green dashed line and the green solid line, respectively. The modeled molar organic yield as a function of time is represented by the solid purple line. In (C), the measured (dashed dark-blue line) and modeled (solid dark-blue line) OOH molar yields and the modeled mass contribution (solid light-blue line) of all compounds containing OOH are shown. See also Figures S7 and S8.
Chem 2016 1, DOI: ( /j.chempr )
Copyright © 2016 Elsevier Inc. Terms and Conditions