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| Titel |
Comparison of OH concentration measurements by DOAS and LIF during SAPHIR chamber experiments at high OH reactivity and low NO concentration |
| VerfasserIn |
H. Fuchs, H.-P. Dorn, M. Bachner, B. Bohn, T. Brauers, S. Gomm, A. Hofzumahaus, F. Holland, S. Nehr, F. Rohrer, R. Tillmann, A. Wahner |
| 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 ; 5, no. 7 ; Nr. 5, no. 7 (2012-07-11), S.1611-1626 |
| Datensatznummer |
250003003
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| Publikation (Nr.) |
 copernicus.org/amt-5-1611-2012.pdf |
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| Zusammenfassung |
| During recent field campaigns, hydroxyl radical (OH) concentrations
that were measured by laser-induced fluorescence (LIF) were up to a factor of
ten larger than predicted by current chemical models for conditions of high
OH reactivity and low NO concentration. These discrepancies,
which were observed in forests and urban-influenced rural environments, are
so far not entirely understood. In summer 2011, a series of experiments was
carried out in the atmosphere simulation chamber SAPHIR in Jülich, Germany,
in order to investigate the photochemical degradation of isoprene,
methyl-vinyl ketone (MVK), methacrolein (MACR) and aromatic compounds by
OH. Conditions were similar to those experienced during the
PRIDE-PRD2006 campaign in the Pearl River Delta (PRD), China, in 2006, where
a large difference between OH measurements and model predictions was
found. During experiments in SAPHIR, OH was simultaneously detected by
two independent instruments: LIF and differential optical absorption
spectroscopy (DOAS). Because DOAS is an inherently calibration-free
technique, DOAS measurements are regarded as a reference standard. The
comparison of the two techniques was used to investigate potential artifacts
in the LIF measurements for PRD-like conditions of OH reactivities of
10 to 30 s−1 and NO mixing ratios of 0.1 to
0.3 ppbv. The analysis of twenty experiment days shows good
agreement. The linear regression of the combined data set (averaged to the
DOAS time resolution, 2495 data points) yields a slope of 1.02 ± 0.01 with
an intercept of (0.10 ± 0.03) × 106 cm−3 and a linear
correlation coefficient of R2 = 0.86. This indicates that the sensitivity of
the LIF instrument is well-defined by its calibration procedure. No hints for
artifacts are observed for isoprene, MACR, and different aromatic compounds.
LIF measurements were approximately 30–40% (median) larger than those by
DOAS after MVK (20 ppbv) and toluene (90 ppbv) had been added. However, this discrepancy has a
large uncertainty and requires further laboratory investigation. Observed
differences between LIF and DOAS measurements are far too small to explain
the unexpected high OH concentrations during the PRIDE-PRD2006
campaign. |
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