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| Titel |
Intercomparison of the comparative reactivity method (CRM) and pump–probe technique for measuring total OH reactivity in an urban environment |
| VerfasserIn |
R. F. Hansen, M. Blocquet, C. Schoemaecker, T. Léonardis, N. Locoge, C. Fittschen, B. Hanoune, P. S. Stevens, V. Sinha, 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. 10 ; Nr. 8, no. 10 (2015-10-14), S.4243-4264 |
| Datensatznummer |
250116636
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| Publikation (Nr.) |
 copernicus.org/amt-8-4243-2015.pdf |
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| Zusammenfassung |
The investigation of hydroxyl radical (OH) chemistry during intensive field
campaigns has led to the development of several techniques dedicated to
ambient measurements of total OH reactivity, which is the inverse of the OH
lifetime. Three techniques are currently used during field campaigns,
including the total OH loss rate method, the pump–probe method, and the
comparative reactivity method. However, no formal intercomparison of these
techniques has been published so far, and there is a need to ensure that
measurements of total OH reactivity are consistent among the different
techniques.
An intercomparison of two OH reactivity instruments, one based on the
comparative reactivity method (CRM) and the other based on the pump–probe
method, was performed in October 2012 in a NOx-rich environment, which
is known to be challenging for the CRM technique. This study presents an
extensive description of the two instruments, the CRM instrument from Mines
Douai (MD-CRM) and the pump–probe instrument from the University of Lille
(UL-FAGE), and highlights instrumental issues associated with the two
techniques.
It was found that the CRM instrument used in this study underestimates
ambient OH reactivity by approximately 20 % due to the photolysis of
volatile organic compounds (VOCs) inside the sampling reactor; this value is
dependent on the position of the lamp within the reactor. However, this issue
can easily be fixed, and the photolysis of VOCs was successfully reduced to a
negligible level after this intercomparison campaign. The UL-FAGE instrument
may also underestimate ambient OH reactivity due to the difficulty to
accurately measure the instrumental zero. It was found that the measurements
are likely biased by approximately 2 s-1, due to impurities in
humid zero air.
Two weeks of ambient sampling indicate that the measurements performed by the
two OH reactivity instruments are in agreement, within the measurement
uncertainties for each instrument, for NOx mixing ratios up to
100 ppbv. The CRM technique has hitherto mainly been used in
low-NOx environments, i.e. environments with ambient NOx mixing ratios
lower than a few ppbv, due to a measurement artifact generated by ambient NO
inside the sampling reactor. However, this study shows that this technique
can also be used under NOx-rich conditions if a NOx-dependent
correction is carefully applied on the OH reactivity measurements.
A full suite of 52 VOCs, NOx, and other inorganic species were
monitored during this intercomparison. An investigation of the OH reactivity
budget for this urban site suggests that this suite of trace gases can
account for the measured total OH reactivity. |
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