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| Titel |
Intercomparison of two comparative reactivity method instruments inf the Mediterranean basin during summer 2013 |
| VerfasserIn |
N. Zannoni, S. Dusanter, V. Gros, R. Sarda Estève, V. Michoud, V. Sinha, N. Locoge, B. Bonsang |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 8, no. 9 ; Nr. 8, no. 9 (2015-09-21), S.3851-3865 |
| Datensatznummer |
250116582
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| Publikation (Nr.) |
 copernicus.org/amt-8-3851-2015.pdf |
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| Zusammenfassung |
The hydroxyl radical (OH) plays a key role in the atmosphere, as it
initiates most of the oxidation processes of volatile organic compounds
(VOCs), and can ultimately lead to the formation of ozone and secondary
organic aerosols (SOAs). There are still uncertainties associated with the OH
budget assessed using current models of atmospheric chemistry and direct
measurements of OH sources and sinks have proved to be valuable tools to
improve our understanding of the OH chemistry.
The total first order loss rate of OH, or total OH reactivity, can be
directly measured using three different methods, such as the following: total OH loss rate
measurement, laser-induced pump and probe technique and comparative
reactivity method. Observations of total OH reactivity are usually coupled
to individual measurements of reactive compounds in the gas phase, which are
used to calculate the OH reactivity. Studies using the three methods have
highlighted that a significant fraction of OH reactivity is often not
explained by individually measured reactive compounds and could be
associated to unmeasured or unknown chemical species. Therefore accurate and
reproducible measurements of OH reactivity are required.
The comparative reactivity method (CRM) has demonstrated to be an
advantageous technique with an extensive range of applications, and for this
reason it has been adopted by several research groups since its development.
However, this method also requires careful corrections to derive ambient OH
reactivity.
Herein we present an intercomparison exercise of two CRM instruments,
CRM-LSCE (Laboratoire des Sciences du Climat et de l'Environnement) and
CRM-MD (Mines Douai), conducted during July 2013 at the Mediterranean site
of Ersa, Cape Corsica, France. The intercomparison exercise included tests
to assess the corrections needed by the two instruments to process the raw
data sets as well as OH reactivity observations. The observation was divided
in three parts: 2 days of plant emissions (8–9 July), 2 days of ambient
measurements (10–11 July) and 2 days (12–13 July) of plant emissions. We
discuss in detail the experimental approach adopted and how the data sets
were processed for both instruments. Corrections required for the two
instruments lead to higher values of reactivity in ambient air; overall
20 % increase for CRM-MD and 49 % for CRM-LSCE compared to the raw data.
We show that ambient OH reactivity measured by the two instruments agrees
very well (correlation described by a linear least squares fit with a slope
of 1 and R2 of 0.75).
This study highlights that ambient measurements of OH reactivity with
differently configured CRM instruments yield consistent results in a low
NOx (NO + NO2), terpene rich environment, despite differential
corrections relevant to each instrument. Conducting more intercomparison
exercises, involving more CRM instruments operated under different ambient
and instrumental settings will help in assessing the variability induced due
to instrument-specific corrections further. |
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