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- ItemImportance of secondary organic aerosol formation of iα/i-pinene, limonene, and im/i-cresol comparing day- And nighttime radical chemistry(Katlenburg-Lindau : European Geosciences Union, 2021) Mutzel, Anke; Zhang, Yanli; Böge, Olaf; Rodigast, Maria; Kolodziejczyk, Agata; Wang, Xinming; Herrmann, HartmutThe oxidation of biogenic and anthropogenic compounds leads to the formation of secondary organic aerosol mass (SOA). The present study aims to investigate span classCombining double low line"inline-formula"iα/i/span-pinene, limonene, and span classCombining double low line"inline-formula"im/i/span-cresol with regards to their SOA formation potential dependent on relative humidity (RH) under night- (NOspan classCombining double low line"inline-formula"3/span radicals) and daytime conditions (OH radicals) and the resulting chemical composition. It was found that SOA formation potential of limonene with NOspan classCombining double low line"inline-formula"3/span under dry conditions significantly exceeds that of the OH-radical reaction, with SOA yields of 15-30 % and 10-21 %, respectively. Additionally, the nocturnal SOA yield was found to be very sensitive towards RH, yielding more SOA under dry conditions. In contrast, the SOA formation potential of span classCombining double low line"inline-formula"iα/i/span-pinene with NOspan classCombining double low line"inline-formula"3/span slightly exceeds that of the OH-radical reaction, independent from RH. On average, span classCombining double low line"inline-formula"iα/i/span-pinene yielded SOA with about 6-7 % from NOspan classCombining double low line"inline-formula"3/span radicals and 3-4 % from OH-radical reaction. Surprisingly, unexpectedly high SOA yields were found for span classCombining double low line"inline-formula"im/i/span-cresol oxidation with OH radicals (3-9 %), with the highest yield under elevated RH (9 %), which is most likely attributable to a higher fraction of 3-methyl-6-nitro-catechol (MNC). While span classCombining double low line"inline-formula"iα/i/span-pinene and span classCombining double low line"inline-formula"im/i/span-cresol SOA was found to be mainly composed of water-soluble compounds, 50-68 % of nocturnal SOA and 22-39 % of daytime limonene SOA are water-insoluble. The fraction of SOA-bound peroxides which originated from span classCombining double low line"inline-formula"iα/i/span-pinene varied between 2 and 80 % as a function of RH./p pFurthermore, SOA from span classCombining double low line"inline-formula"iα/i/span-pinene revealed pinonic acid as the most important particle-phase constituent under day- and nighttime conditions with a fraction of 1-4 %. Other compounds detected are norpinonic acid (0.05-1.1 % mass fraction), terpenylic acid (0.1-1.1 % mass fraction), pinic acid (0.1-1.8 % mass fraction), and 3-methyl-1,2,3-tricarboxylic acid (0.05-0.5 % mass fraction). All marker compounds showed higher fractions under dry conditions when formed during daytime and showed almost no RH effect when formed during night./p © 2021 Copernicus GmbH. All rights reserved.
- ItemDevelopment of a protocol for the auto-generation of explicit aqueous-phase oxidation schemes of organic compounds(Katlenburg-Lindau : EGU, 2019) Bräuer, Peter; Mouchel-Vallon, Camille; Tilgner, Andreas; Mutzel, Anke; Böge, Olaf; Rodigast, Maria; Poulain, Laurent; van Pinxteren, Dominik; Wolke, Ralf; Aumont, Bernard; Herrmann, HartmutThis paper presents a new CAPRAM-GECKOA protocol for mechanism auto-generation of aqueous-phase organic processes. For the development, kinetic data in the literature were reviewed and a database with 464 aqueousphase reactions of the hydroxyl radical with organic compounds and 130 nitrate radical reactions with organic compounds has been compiled and evaluated. Five different methods to predict aqueous-phase rate constants have been evaluated with the help of the kinetics database: gas-aqueous phase correlations, homologous series of various compound classes, radical reactivity comparisons, Evans-Polanyi-type correlations, and structure-activity relationships (SARs). The quality of these prediction methods was tested as well as their suitability for automated mechanism construction. Based on this evaluation, SARs form the basis of the new CAPRAM-GECKO-A protocol. Evans-Polanyi-type correlations have been advanced to consider all available H atoms in a molecule besides the H atoms with only the weakest bond dissociation enthalpies (BDEs). The improved Evans- Polanyi-type correlations are used to predict rate constants for aqueous-phase NO3 and organic compounds reactions. Extensive tests have been performed on essential parameters and on highly uncertain parameters with limited experimental data. These sensitivity studies led to further improvements in the new CAPRAM-GECKO-A protocol but also showed current limitations. Biggest uncertainties were observed in uptake processes and the estimation of Henry's law coefficients as well as radical chemistry, in particular the degradation of alkoxy radicals. Previous estimation methods showed several deficits, which impacted particle growth. For further evaluation, a 1,3,5-trimethylbenzene oxidation experiment has been performed in the aerosol chamber "Leipziger Aerosolkammer" (LEAK) at high relative humidity conditions and compared to a multiphase mechanism using the Master Chemical Mechanism (MCMv3.2) in the gas phase and using a methylglyoxal oxidation scheme of about 600 reactions generated with the new CAPRAM-GECKO-A protocol in the aqueous phase. While it was difficult to evaluate single particle constituents due to concentrations close to the detection limits of the instruments applied, the model studies showed the importance of aqueous-phase chemistry in respect to secondary organic aerosol (SOA) formation and particle growth. The new protocol forms the basis for further CAPRAM mechanism development towards a new version 4.0. Moreover, it can be used as a supplementary tool for aerosol chambers to design and analyse experiments of chemical complexity and help to understand them on a molecular level. © 2019 Author(s).