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| Titel |
Detailed characterization of a Comparative Reactivity Method (CRM) instrument for ambient OH reactivity measurements: experiments vs. modeling |
| VerfasserIn |
Vincent Michoud, Nadine Locoge, Sébastien Dusanter |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250106102
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| Publikation (Nr.) |
 EGU/EGU2015-5756.pdf |
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| Zusammenfassung |
| The Hydroxyl radical (OH) is the main daytime oxidant in the troposphere, leading to the
oxidation of Volatile Organic Compounds (VOCs) and the formation of harmful pollutants
such as ozone (O3) and Secondary Organic Aerosols (SOA). While OH plays a key role in
tropospheric chemistry, recent studies have highlighted that there are still uncertainties
associated with the OH budget, i.e the identification of sources and sinks and the
quantification of production and loss rates of this radical. It has been demonstrated that
ambient measurements of the total OH loss rate (also called total OH reactivity) can be
used to identify and reduce these uncertainties. In this context, the Comparative
Reactivity Method (CRM), developed by Sinha et al. (ACP, 2008), is a promising
technique to measure total OH reactivity in ambient air and has already been used
during several field campaigns. This technique relies on monitoring competitive
reactions of OH with ambient trace gases and a reference compound (pyrrole) in a
sampling reactor to derive ambient OH reactivity. However, this technique requires
a complex data processing chain that has yet to be carefully investigated in the
laboratory.
In this study, we present a detailed characterization of a CRM instrument developed at
Mines Douai, France. Experiments have been performed to investigate the dependence of the
CRM response on humidity, ambient NOx levels, and the pyrrole-to-OH ratio inside the
sampling reactor. Box modelling of the chemistry occurring in the reactor has also been
performed to assess our theoretical understanding of the CRM measurement. This work
shows that the CRM response is sensitive to both humidity and NOx, which can be
accounted for during data processing using parameterizations depending on the
pyrrole-to-OH ratio. The agreement observed between laboratory studies and model results
suggests a good understanding of the chemistry occurring in the sampling reactor and gives
confidence in the CRM measurements. We will present the data processing that is needed to
derive reliable OH reactivity values from CRM measurements and will discuss the limitations
of this technique. |
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