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@BOOK{Nehr:22995,
author = {Nehr, Sascha},
title = {{M}echanistic studies on the {OH}-initiated atmospheric
oxidation of selected aromatic hydrocarbons},
volume = {145},
school = {Universität Wuppertal},
type = {Dr.},
address = {Jülich},
publisher = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
reportid = {PreJuSER-22995, D 468},
isbn = {978-3-89336-804-4},
series = {Schriften des Forschungszentrums Jülich : Energie $\&$
Umwelt / Energy $\&$ Environment},
pages = {VIII, 129 S.},
year = {2012},
note = {Record converted from JUWEL: 18.07.2013; Universität
Wuppertal, Diss., 2012},
abstract = {Benzene, toluene, the xylenes, and the trimethylbenzenes
are among the most abundant aromatic trace constituents of
the atmosphere mainly originating from anthropogenic
sources. The OH-initiated atmospheric photo-oxidation of
aromatic hydrocarbons is the predominant removal process
resulting in the formation of O$_{3}$ and secondary organic
aerosol. Therefore, aromatics are important trace
constituents regarding air pollution in urban environments.
Our understanding of aromatic photo-oxidation processes is
far from being complete. This work presents novel approaches
for the investigation of OH-initiated atmospheric
degradation mechanisms of aromatic hydrocarbons. Firstly,
pulsed kinetic studies were performed to investigate the
prompt HO$_{2}$ formation from OH + aromatic hydrocarbon
reactions under ambient conditions. For these studies, the
existing OH reactivity instrument, based on the flash
photolysis/laser-induced fluorescence (FP/LIF) technique,
was extended to the detection of HO2 radicals. The
experimental design allows for the determination of HO$_{2}$
formation yields and kinetics. Results of the pulsed kinetic
experiments complement previous product studies and help to
reduce uncertainties regarding the primary oxidation steps.
Secondly, experiments with aromatic hydrocarbons were
performed under atmospheric conditions in the outdoor
atmosphere simulation chamber SAPHIR (Simulation of
Atmospheric PHotochemistry In a large Reaction chamber)
located at Forschungszentrum Jülich. The experiments were
aimed at the evaluation of up-to-date aromatic degradation
schemes of the Master Chemical Mechanism (MCMv3.2). The
unique combination of analytical instruments operated at
SAPHIR allows for a detailed investigation of HO$_{x}$ and
NO$_{x}$ budgets and for the determination of primary
phenolic oxidation product yields. MCMv3.2 deficiencies were
identified and most likely originate from short-comings in
the mechanistic representation of ring fragmentation
channels. These shortcomings relate to the formation of
peroxy radicals, the NO to NO$_{2}$ conversion, and the O3
production. Conceptual ideas were presented to overcome
these MCMv3.2 shortcomings and an improved reaction
mechanism was constructed. However, major eficiencies still
remain that require further investigations. Regarding the
primary oxidation steps, the results of this work confirm
the current MCMv3.2 recommendations. Proposed primary
oxidation products are, e.g., phenols and epoxides. Phenol
yields are in line with the MCMv3.2 values. The results of
the complementary pulsed kinetic studies are consistent with
the proposed combined formation yields of phenols plus
epoxides. So far, epoxides have only been identified
tentatively and the results of this work provide more
quantitative information.},
cin = {IEK-8},
ddc = {500},
cid = {I:(DE-Juel1)IEK-8-20101013},
pnm = {Atmosphäre und Klima},
pid = {G:(DE-Juel1)FUEK491},
typ = {PUB:(DE-HGF)3},
url = {https://juser.fz-juelich.de/record/22995},
}