TY - JOUR A1 - Novelli, Anna A1 - Kaminski, Martin A1 - Rolletter, Michael A1 - Acir, Ismail-Hakki A1 - Bohn, Birger A1 - Dorn, Hans-Peter A1 - Li, Xin A1 - Lutz, Anna A1 - Nehr, Sascha A1 - Rohrer, Franz A1 - Tillmann, Ralf A1 - Wegener, Robert A1 - Holland, Frank A1 - Hofzumahaus, Andreas A1 - Kiendler-Scharr, Astrid A1 - Wahner, Andreas A1 - Fuchs, Hendrik T1 - Evaluation of OH and HO2 concentrations and their budgets during photooxidation of 2-methyl-3-butene-2-ol (MBO) in the atmospheric simulation chamber SAPHIR JF - Atmospheric Chemistry and Physics N2 - Several previous field studies have reported unexpectedly large concentrations of hydroxyl and hydroperoxyl radicals (OH and HO2, respectively) in forested environments that could not be explained by the traditional oxidation mechanisms that largely underestimated the observations. These environments were characterized by large concentrations of biogenic volatile organic compounds (BVOC) and low nitrogen oxide concentration. In isoprene-dominated environments, models developed to simulate atmospheric photochemistry generally underestimated the observed OH radical concentrations. In contrast, HO2 radical concentration showed large discrepancies with model simulations mainly in non-isoprene-dominated forested environments. An abundant BVOC emitted by lodgepole and ponderosa pines is 2-methyl-3-butene-2-ol (MBO), observed in large concentrations for studies where the HO2 concentration was poorly described by model simulations. In this work, the photooxidation of MBO by OH was investigated for NO concentrations lower than 200 pptv in the atmospheric simulation chamber SAPHIR at Forschungszentrum Jülich. Measurements of OH and HO2 radicals, OH reactivity (kOH), MBO, OH precursors, and organic products (acetone and formaldehyde) were used to test our current understanding of the OH-oxidation mechanisms for MBO by comparing measurements with model calculations. All the measured trace gases agreed well with the model results (within 15 %) indicating a well understood mechanism for the MBO oxidation by OH. Therefore, the oxidation of MBO cannot contribute to reconciling the unexplained high OH and HO2 radical concentrations found in previous field studies. KW - Luftreinhaltung Y1 - 2018 U6 - https://doi.org/10.5194/acp-18-11409-2018 SN - 1680-7324 N1 - Code and data availability The data from the experiments in the SAPHIR chamber used in this work are available on the EUROCHAMP data home page (https://data.eurochamp.org/, last access: 1 October 2019, EUROCHAMP, 2019). Supplement The supplement related to this article is available online at: https://doi.org/10.5194/acp-20-3333-2020-supplement. VL - 18 IS - 15 SP - 11409 EP - 11422 PB - Copernicus ER - TY - JOUR A1 - Rolletter, Michael A1 - Kaminski, Martin A1 - Acir, Ismail-Hakki A1 - Bohn, Birger A1 - Dorn, Hans-Peter A1 - Li, Xin A1 - Lutz, Anna A1 - Nehr, Sascha A1 - Rohrer, Franz A1 - Tillmann, Ralf A1 - Wegener, Robert A1 - Hofzumahaus, Andreas A1 - Kiendler-Scharr, Astrid A1 - Wahner, Andreas A1 - Fuchs, Hendrik T1 - Investigation of the α-pinene photooxidation by OH in the atmospheric simulation chamber SAPHIR JF - Atmospheric Chemistry and Physics N2 - Abstract. The photooxidation of the most abundant monoterpene, α-pinene, by the hydroxyl radical (OH) was investigated at atmospheric concentrations in the atmospheric simulation chamber SAPHIR. Concentrations of nitric oxide (NO) were below 120 pptv. Yields of organic oxidation products are determined from measured time series giving values of 0.11±0.05, 0.19±0.06, and 0.05±0.03 for formaldehyde, acetone, and pinonaldehyde, respectively. The pinonaldehyde yield is at the low side of yields measured in previous laboratory studies, ranging from 0.06 to 0.87. These studies were mostly performed at reactant concentrations much higher than observed in the atmosphere. Time series of measured radical and trace-gas concentrations are compared to results from model calculations applying the Master Chemical Mechanism (MCM) 3.3.1. The model predicts pinonaldehyde mixing ratios that are at least a factor of 4 higher than measured values. At the same time, modeled hydroxyl and hydroperoxy (HO2) radical concentrations are approximately 25 % lower than measured values. Vereecken et al. (2007) suggested a shift of the initial organic peroxy radical (RO2) distribution towards RO2 species that do not yield pinonaldehyde but produce other organic products. Implementing these modifications reduces the model–measurement gap of pinonaldehyde by 20 % and also improves the agreement in modeled and measured radical concentrations by 10 %. However, the chemical oxidation mechanism needs further adjustment to explain observed radical and pinonaldehyde concentrations. This could be achieved by adjusting the initial RO2 distribution, but could also be done by implementing alternative reaction channels of RO2 species that currently lead to the formation of pinonaldehyde in the model. KW - Luftreinhaltung Y1 - 2019 U6 - https://doi.org/10.5194/acp-19-11635-2019 SN - 1680-7324 N1 - Data availability Data of the experiments in the SAPHIR chamber used in this work are available on the EUROCHAMP data home page (https://data.eurochamp.org/, last access: 28 April 2019, Eurochamp, 2019). Supplement The supplement related to this article is available online at: https://doi.org/10.5194/acp-19-11635-2019-supplement. VL - 19 IS - 18 SP - 11635 EP - 11649 PB - Copernicus ER - TY - JOUR A1 - Kaminski, Martin A1 - Fuchs, Hendrik A1 - Acir, Ismail-Hakki A1 - Bohn, Birger A1 - Brauers, Theo A1 - Dorn, Hans-Peter A1 - Häseler, Rolf A1 - Hofzumahaus, Andreas A1 - Li, Xin A1 - Lutz, Anna A1 - Nehr, Sascha A1 - Rohrer, Franz A1 - Tillmann, Ralf A1 - Vereecken, Luc A1 - Wegener, Robert A1 - Wahner, Andreas T1 - Investigation of the β-pinene photooxidation by OH in the atmosphere simulation chamber SAPHIR JF - Atmospheric Chemistry and Physics N2 - Abstract. Besides isoprene, monoterpenes are the non-methane volatile organic compounds (VOCs) with the highest global emission rates. Due to their high reactivity towards OH, monoterpenes can dominate the radical chemistry of the atmosphere in forested areas. In the present study the photochemical degradation mechanism of β-pinene was investigated in the Jülich atmosphere simulation chamber SAPHIR (Simulation of Atmospheric PHotochemistry In a large Reaction Chamber). One focus of this study is on the OH budget in the degradation process. Therefore, the SAPHIR chamber was equipped with instrumentation to measure radicals (OH, HO2, RO2), the total OH reactivity, important OH precursors (O3, HONO, HCHO), the parent VOC β-pinene, its main oxidation products, acetone and nopinone and photolysis frequencies. All experiments were carried out under low-NO conditions ( ≤  300 ppt) and at atmospheric β-pinene concentrations ( ≤  5 ppb) with and without addition of ozone. For the investigation of the OH budget, the OH production and destruction rates were calculated from measured quantities. Within the limits of accuracy of the instruments, the OH budget was balanced in all β-pinene oxidation experiments. However, even though the OH budget was closed, simulation results from the Master Chemical Mechanism (MCM) 3.2 showed that the OH production and destruction rates were underestimated by the model. The measured OH and HO2 concentrations were underestimated by up to a factor of 2, whereas the total OH reactivity was slightly overestimated because the model predicted a nopinone mixing ratio which was 3 times higher than measured. A new, theory-derived, first-generation product distribution by Vereecken and Peeters (2012) was able to reproduce the measured nopinone time series and the total OH reactivity. Nevertheless, the measured OH and HO2 concentrations remained underestimated by the numerical simulations. These observations together with the fact that the measured OH budget was closed suggest the existence of unaccounted sources of HO2. Although the mechanism of additional HO2 formation could not be resolved, our model studies suggest that an activated alkoxy radical intermediate proposed in the model of Vereecken and Peeters (2012) generates HO2 in a new pathway, whose importance has been underestimated so far. The proposed reaction path involves unimolecular rearrangement and decomposition reactions and photolysis of dicarbonyl products, yielding additional HO2 and CO. Further experiments and quantum chemical calculations have to be made to completely unravel the pathway of HO2 formation. KW - Luftreinhaltung Y1 - 2017 U6 - https://doi.org/10.5194/acp-17-6631-2017 SN - 1680-7324 VL - 17 IS - 11 SP - 6631 EP - 6650 PB - Copernicus ER -