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| Titel |
Secondary HO2 formation from the OH-initiated photo-oxidation of aromatic hydrocarbons under atmospheric conditions in the absence of NO |
| VerfasserIn |
Sascha Nehr, Birger Bohn, Hendrik Fuchs, Andreas Hofzumahaus |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050891
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| Zusammenfassung |
| Benzene, toluene and the xylenes are among the most abundant aromatic trace constituents of
the atmosphere originating mainly from anthropogenic sources including evaporative
emissions of chemical plants and storage tanks as well as incomplete combustion
processes.[1] In the troposphere, the photo-oxidation of aromatic hydrocarbons results in the
formation of ozone and secondary organic aerosol. Therefore, aromatics are important trace
constituents regarding air pollution levels.[2]
The reaction of OH radicals with aromatics proceeds mainly via addition to
form the OH-aromatic-adduct. Under ambient conditions, the dominant fate of the
OH-aromatic-adduct is the reaction with O2. These subsequent O2 reactions are
yielding ring-retaining and ring-cleavage oxidation products, partly after reaction with
NO. However, the reaction mechanisms and the product yields of these subsequent
reactions are still not well known. The currently recommended main products of the
ring-retaining degradation pathways are phenolic compounds + HO2, whereas unsaturated
epoxy-dicarbonyl-compounds + HO2 or intermediate peroxy radicals are the proposed
products of the ring-cleavage pathways. It has been shown, that the ring-cleavage pathways
are more efficient at generating ozone.[3] Thus, the product yields of the OH-aromatic-adduct
+ O2 reaction are important for the impact of aromatic compounds on atmospheric
chemistry.
We performed pulsed kinetic experiments in different N2/O2 mixtures at atmospheric
pressure and room temperature in the absence of NO in order to investigate the
secondary HO2 formation from the OH-initiated degradation of several aromatic
hydrocarbons. OH was formed in a reaction cell under laminar flow conditions by laser
flash photolysis of O3 at 266 nm followed by reaction of O(1D) with water vapour.
OH and HOx (=OH+HO2) decay curves were detected by means of laser-induced
fluorescence technique (LIF). We observed HOx decay curves for the first time and
extracted total HO2 yields as well as reaction rate constants by employing analytical
solutions and curve-fitting procedures. Experiments with deuterated aromatics were
performed to further elucidate the degradation mechanisms and to differentiate
between HO2 formation resulting from ring-retaining and ring-cleavage reaction
channels.
References:
[1] T.J. Fortin, B.J. Howard, D.D. Parrish, P.D. Goldan, W.C. Kuster, E.L. Atlas, R.A.
Harley, Environmental Science and Technology, 2005, 39, 1403-1408
[2] J. G. Calvert, R. Atkinson, K.H. Becker, R.M. Kamens, J.H. Seinfeld, T.J. Wallington,
G. Yarwood: The mechanisms of atmospheric oxidation of aromatic hydrocarbons, Oxford
University Press, 2002
[3] C. Bloss, V. Wagner, A. Bonzanini, M.E. Jenkin, K. Wirtz, M. Martin-Reviejo, M.J.
Pilling, Atmospheric Chemistry and Physics, 2005, 5, 623-639 |
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