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| Titel |
Cavity ring-down spectroscopy sensor development for high-time-resolution measurements of gaseous elemental mercury in ambient air |
| VerfasserIn |
A. Pierce, D. Obrist, H. Moosmüller, X. Faïn, C. Moore |
| 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 ; 6, no. 6 ; Nr. 6, no. 6 (2013-06-05), S.1477-1489 |
| Datensatznummer |
250017906
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| Publikation (Nr.) |
 copernicus.org/amt-6-1477-2013.pdf |
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| Zusammenfassung |
We describe further development of a previous
laboratory prototype pulsed cavity ring-down spectroscopy (CRDS) sensor into
a field-deployable system for high-time-resolution, continuous, and automated
measurement of gaseous elemental mercury (GEM) concentrations in ambient air.
We employed an external, isotopically enriched Hg cell for automated locking
and stabilization of the laser wavelength on the GEM peak absorption during
measurements. Further, we describe implementation of differential absorption
measurements via a piezoelectric tuning element for pulse-by-pulse tuning of
the laser wavelength onto and off of the GEM absorption line. This allowed us
to continuously correct (at 25 Hz) for system baseline extinction losses
unrelated to GEM absorption.
Extensive measurement and calibration data obtained with the system were
based on spike addition in both GEM-free air and ambient air. Challenges and
interferences that occurred during measurements (particularly in ambient air)
are discussed including temperature and ozone (O3) concentration
fluctuations, and steps taken to reduce these. CRDS data were highly linear
(r2 ≥ 0.98) with data from a commercial Tekran 2537 Hg analyzer
across a wide range of GEM concentrations (0 to 127 ng m−3) in Hg-free
and ambient air. Measurements during periods of stable background GEM
concentrations provided a conservative instrument sensitivity estimate of
0.35 ng m−3 for the CRDS system when time averaged for 5 min. This
sensitivity, along with concentration patterns observed in ambient air (with
the CRDS system and verified with the Tekran analyzer), showed that the
sensor was capable of characterizing GEM fluctuations in
ambient air. The value of fast-response GEM measurements was shown by a
series of GEM spike additions – highlighting that high-temporal-resolution
measurement allowed for detailed characterization of fast concentration
fluctuations not possible with traditional analyzers. |
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