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| Titel |
Detailed characterizations of the new Mines Douai comparative reactivity method instrument via laboratory experiments and modeling |
| VerfasserIn |
V. Michoud, R. F. Hansen, N. Locoge, P. S. Stevens, S. Dusanter |
| 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. 8 ; Nr. 8, no. 8 (2015-08-31), S.3537-3553 |
| Datensatznummer |
250116548
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| Publikation (Nr.) |
 copernicus.org/amt-8-3537-2015.pdf |
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| Zusammenfassung |
The hydroxyl (OH) radical is an important oxidant in the troposphere, which
controls the lifetime of most air quality- and climate-related trace gases.
However, there are still uncertainties concerning its atmospheric budget, and
integrated measurements of OH sinks have been valuable to improve this
aspect. Among the analytical tools used for measuring total OH reactivity in
ambient air, the comparative reactivity method (CRM) is spreading rapidly in
the atmospheric community. However, measurement artifacts have been
highlighted for this technique, and additional work is needed to fully
characterize them.
In this study, we present the new Mines Douai CRM instrument, with an
emphasis on the corrections that need to be applied to ambient measurements
of total OH reactivity. Measurement artifacts identified in the literature
have been investigated, including (1) a correction for a change in relative
humidity between the measurement steps leading to different OH levels, (2)
the formation of spurious OH in the sampling reactor when hydroperoxy
radicals (HO2) react with nitrogen monoxide (NO), (3) not operating the
CRM under pseudo-first-order kinetics, and (4) the dilution of ambient air
inside the reactor. The dependences of these artifacts on various measurable
parameters, such as the pyrrole-to-OH ratio and the bimolecular reaction
rate constants of ambient trace gases with OH, have also been studied. Based
on these observations, parameterizations are proposed to correct ambient OH
reactivity measurements. On average, corrections of 5.2 ± 3.2,
9.2 ± 15.7, and 8.5 ± 5.8 s−1 were respectively
observed for (1), (2) and (3) during a field campaign performed in Dunkirk,
France (summer 2014).
Numerical simulations have been performed using a box model to check whether
experimental observations mentioned above are consistent with our
understanding of the chemistry occurring in the CRM reactor. Two different
chemical mechanisms have been shown to reproduce the magnitude of
corrections (2) and (3). In addition, these simulations reproduce their
dependences on the pyrrole-to-OH ratio and on bimolecular reaction rate
constants of gases reacting with OH. The good agreement found between
laboratory experiments and model simulations gives us confidence in the
proposed parameterizations. However, it is worth noting that the numerical
values given in this study are suitable for the Mines Douai instrument and
may not be appropriate for other CRM instruments. It is recommended that
each group characterize its own instrument following the recommendations
given in this study.
An assessment of performances for the Mines Douai instrument, including a
propagation of errors from the different corrections, indicates a limit of
detection of 3.0 s−1 and total uncertainties of 17–25 % for OH
reactivity values higher than 15 s−1 and NOx mixing ratios lower
than 30 ppbv. |
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