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| Titel |
Infrared Faraday Rotation Spectroscopy for Monitoring of the atmospheric oxidation capacity |
| VerfasserIn |
Weixiong Zhao, Gerard Wysocki, Weidong Chen, Eric Fertein, Denis Petitprez, Weijun Zhang |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250034947
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| Zusammenfassung |
| Hydroxyl (OH) free radical is a key oxidizing species in the Earth’s atmosphere. Because
of its high reactivity, interference-free high sensitivity in situ monitoring of OH
represents a real challenge. Faraday rotation spectroscopy (FRS) takes advantage of the
particular magneto-optic effect observed for paramagnetic species. When a longitudinal
magnetic field is applied, the magnetic circular birefringence is observed in the
vicinity of Zeeman splitted absorption lines, and the polarization axis of a linearly
polarized light is rotated due to interaction with the sample. This makes FRS capable of
enhancing the detection sensitivity and completely eliminating interference from
the diamagnetic species in the atmosphere such as CO2 and H2O. For OH free
radicals, the highest absorption line strength and the largest gJ value make the Q
(1.5) double lines of the 2Î 3-2 (Ï
=1-0) state at 2.8 μm clearly the best choice for
sensitive detection in the infrared region by FRS. In this paper we report on the
development of an FRS instrument based on a DFB diode laser operating at 2.8 μm. The
prototype instrument with an active optical pathlength of only 25 cm and a lock-in
time constant of 300 ms, achieves a 1Ï detection limit of 3.5Ã1010 radicals/cm3.
Substantial improvements of the instrumental components are currently ongoing
and will be reported in details. Based on the conservative estimates the detection
sensitivity of ~107 radicals/cm3 can be attained which is suitable for high accuracy
atmospheric chemistry studies in environmental photoreactor chambers and for direct
measurement of total reaction rate of OH in the atmosphere under atmospheric pressure. |
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