This title appears in the Scientific Report : 2014 
Untersuchung des photochemischen Terpenoidabbaus in der Atmosphärensimulationskammer SAPHIR
Kaminski, Martin (Corresponding author)
Troposphäre; IEK-8
2014
Jülich Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag 2014
148 S.
Universität Köln, Diss., 2014
987-3-89336-967-6
Dissertation / PhD Thesis
Trace gas and aerosol processes in the troposphere
Schriften des Forschungszentrums Jülich Reihe Energie & Umwelt / Energy & Environment 218
Dissertation > Diss.
OpenAccess
Please use the identifier: http://hdl.handle.net/2128/7853 in citations.


The hydroxyl radical (OH) is the main oxidation agent in the atmosphere during daytime. Recent field campaigns studying the radical chemistry in forested areas showed large discrepancies between measured and modeled OH concentration at low NO$_{x}$ conditions and a VOC dominated OH reactivity k(OH) (Hofzumahaus et al., 2009; Lelieveld et al., 2008). These observations were only partially explained by the evidence for new efficient hydroxyl radical regeneration pathways in the isoprene oxidation mechanism (Fuchs et al., 2013; Whalley et al., 2011). So it is likely that other VOC species are also capable of additional OH recycling. Beside isoprene monoterpenes and 2-methyl-3-buten-2-ol (MBO) belong to the volatile organic compound (VOC) species with the highest global emission rates. Due to their high reactivity towards OH, monoterpenes and MBO can dominate the radical chemistry of the atmosphere in forested areas under certain conditions (Kim et al., 2013). In the present study the photochemical degradation mechanism of $\alpha$-pinene, $\beta$-pinene, limonene, myrcene and MBO was investigated in the atmosphere simulation chamber SAPHIR. The focus of this study was in particular on the investigation of the radical budget in the degradation process. The photochemical degradation of the five terpenoids was studied in a dedicated series of experiments in the years 2012 and 2013. The SAPHIR chamber was equipped with instrumentation to measure all important OH precursors (O$_{3}$, HONO, HCHO), the parent VOC and its main oxidation products, radicals (OH, HO$_{2}$, RO$_{2}$), the total OH reactivity, and photolysis frequencies to investigate the radical budget in the chamber. All experiments were carried out under low NOx conditions (≤ 2ppb) and atmospheric terpenoid concentrations (≤ 5ppb) with and without the addition of ozone. The intercomparison of the measured time series of the atmospheric trace gases with simulations using the atmospheric box model Master Chemical Mechanism (MCM) 3.2 showed that the MBO experiments could be described well by the MCM. In contrast to MBO the measured OH and HO$_{2}$ concentrations in the simulations of the $\alpha$-pinene, $\beta$- pinene and limonene experiments were systematically underestimated. In addition the measured k(OH) was overestimated increasingly by the MCM model after VOC injection in the atmosphere simulation chamber. A sensitivity study showed that this overestimation is related to the product spectrum assumed in the MCM model. Despite adjusting the modelled k(OH) to the measured values the measured OH and HO2 concentrations were still underestimated by the model. Model sensitivity studies on additional OH [...]