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| Titel |
Static magnetic Faraday rotation spectroscopy combined with a differential scheme for OH detection |
| VerfasserIn |
Weixiong Zhao, Lunhua Deng, Xiaodong Qian, Bo Fang, Yanbo Gai, Weidong Chen, Xiaoming Gao, Weijun Zhang |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250103134
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| Publikation (Nr.) |
 EGU/EGU2015-2533.pdf |
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| Zusammenfassung |
| The hydroxyl (OH) radical plays a critical role in atmospheric chemistry due to its high
reactivity with volatile organic compounds (VOCs) and other trace gaseous species.
Because of its very short life time and very low concentration in the atmosphere,
interference-free high sensitivity in-situ OH monitoring by laser spectroscopy represents a
real challenge.
Faraday rotation spectroscopy (FRS) relies on the particular magneto-optic effect
observed for paramagnetic species, which makes it capable of enhancing the detection
sensitivity and mitigation of spectral interferences from diamagnetic species in the
atmosphere. When an AC magnetic field is used, the Zeeman splitting of the molecular
absorption line (and thus the magnetic circular birefringence) is modulated. This provides an
“internal modulation” of the sample, which permits to suppress the external noise
like interference fringes. An alternative FRS detection scheme is to use a static
magnetic field (DC-field) associated with laser wavelength modulation to effectively
modulate the Zeeman splitting of the absorption lines. In the DC field case, wavelength
modulation of the laser frequency can provide excellent performance compared to
most of the sensing systems based on direct absorption and wavelength modulation
spectroscopy.
The dimension of the DC solenoid is not limited by the resonant frequency of
the RLC circuit, which makes large dimension solenoid coil achievable and the
absorption base length could be further increased. By employing a combination of the
environmental photochemical reactor or smog chamber with multipass absorption cell, one
can lower the minimum detection limit for high accuracy atmospheric chemistry
studies. In this paper, we report on the development of a DC field based FRS in
conjunction with a balanced detection scheme for OH radical detection at 2.8 μm and the
construction of OH chemistry research platform which combined a large dimension
superconducting magnetic coil with the multipass cell and photochemical reactor
chamber for real time in-situ measurement of OH radical concentration in the chamber. |
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