High sensitivity Faraday rotation spectrometer for hydroxyl radical detection at 2.8 μm

Zhao, Wei; Wysocki, Gerard; Chen, W.; Zhang, W.

doi:10.1007/s00340-012-5089-3

Cited by 17 publications

(9 citation statements)

References 20 publications

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“…19 Wavelength modulation spectroscopy (WMS) combined with a static magnetic field (DCfield) was used to efficiently modulate the Zeeman splitting of the absorption line. 20 The laser frequency was tuned in two ways: 21 (1) a point-by-point tuning method, using a GPIB card to control the laser injection current at each step; (2) a wavelength sweeping method, scanning the laser injection current with a continuous ramp provided by a function generator. For WMS detection, a sinusoidal modulation with a frequency (f m ) of 50 kHz from a lock-in amplifier (SR865, Stanford Research) was added to the injection current.…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…The signal detected by the detector is demodulated (second-harmonic, 2 f detection) by the lock-in amplifier with a time constant of 300 μs to obtain the FRS signal. For weak absorptions, the FRS signal is proportional to the radical concentration ( N ) and absorption path length ( L ): − where ν is the frequency, η is a fixed instrumentation factor, S is the absorption line intensity, P 0 is the incident laser power, φ is the offset angle of the two polarizer, and χ(ν) is the line shape function.…”

Section: Methodsmentioning

confidence: 99%

“…The OH decay was directly measured using a time-resolved FRS spectrometer at 2.8 μm. [19][20][21] FRS is based on the magneto-optic effect of paramagnetic species, which provides a powerful tool for gas phase chemical kinetic studies with high precision, high selectivity, and free of interferences from precursor's absorption. [22][23][24][25] Further improvements can make the system more compact, portable, and affordable, which provides a reliable approach for long-term and network k' OH observations.…”

mentioning

confidence: 99%

“…In this work, we report the development of a new instrument that combines laser-flash photolysis with mid-infrared Faraday rotation spectroscopy (LFP-FRS) for real-time in situ measurement of k OH ′ and free radical kinetics studies. The OH decay was directly measured using a time-resolved FRS spectrometer at 2.8 μm. − FRS is based on the magneto-optic effect of paramagnetic species, which provides a powerful tool for gas phase chemical kinetic studies with high precision, high selectivity, and free of interferences from the precursor’s absorption. − Further improvements can make the system more compact, portable, and affordable, which provides a reliable approach for long-term and network k OH ′ observations.…”

mentioning

confidence: 99%

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Time-Resolved Laser-Flash Photolysis Faraday Rotation Spectrometer: A New Tool for Total OH Reactivity Measurement and Free Radical Kinetics Research

et al. 2020

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The total OH reactivity (k' OH ) is an important parameter for quantitative assessment of the atmospheric oxidation capacity. Although laboratory measurement of k' OH has been achieved 20 years ago, the instruments required are often costly and complex. Long-term atmospheric observations remain challenging and elusive. In this work, a novel instrument combining laserflash photolysis with a mid-infrared Faraday rotation spectrometer (LFP-FRS) has been developed for the measurement of k' OH and for studying gas phase free radical kinetics. The reactor is composed of a Herriott-type optical multipass cell, and OH radicals were generated by flash photolysis of ozone with a 266 nm pulsed Nd:YAG laser. The decay of the OH signal was directly measured with a time-resolved FRS spectrometer at 2.8 μm. The overlapping pathlength between the pump beam and probe beam was 25 m. Increased performance was achieved by subtracting the signals before and after flash photolysis to eliminate interferences caused by H 2 O absorption and background drift. The optimum precisions (1σ) of OH concentration and k' OH measurement were 4×10 6 molecule cm -3 and 0.09 s -1 over data acquisition times of 56 s and 112 s, respectively. The performance of the system was evaluated by the reaction of OH with CO and NO. The measured rate coefficients (k OH+CO and k OH+NO ) were in good agreement with values reported in the literature. The developed LFP-FRS provides a new, high precision, and highly selective tool for atmospheric chemistry research of OH radicals and other transient paramagnetic free radicals such as HO 2 radicals.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Time-Resolved Laser-Flash Photolysis Faraday Rotation Spectrometer: A New Tool for Total OH Reactivity Measurement and Free Radical Kinetics Research

et al. 2020

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Photonic Sensing of Reactive Atmospheric Species

Chen

et al. 2017

Encyclopedia of Analytical Chemistry

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Chemically reactive short‐lived atmospheric species play a crucial role in tropospheric processes that affect regional air quality and global climate change. Contrary to long‐lived species (such as greenhouse gases), fast, interference‐free, accurate, and precise in situ monitoring of such strongly reactive species represents a real challenge owing to their very high reactivity resulting in short lifetimes (∼1–100 s) and ultralow concentrations (∼pptv). In this article, we give an overview of the recent progress in the development of absorption spectroscopy‐based photonic instruments involving modern photonic light sources (quantum cascade laser, distributed feedback diode laser, and light‐emitting diode) combined with high‐sensitivity spectroscopic measurement techniques such as incoherent broadband cavity‐enhanced absorption spectroscopy, Faraday rotation spectroscopy, wavelength‐modulation‐enhanced off‐axis integrated cavity output spectroscopy, tuning fork‐ or microphone‐based photoacoustic spectroscopy, and open‐path multipass absorption spectroscopy. Illustrative examples of monitoring some key atmospheric reactive species (such as HONO, OH, NO 3 , N 2 O 5 , and NO 2 ) will be presented for applications in intensive field campaigns, instrumented atmospheric simulation chamber, or laboratory investigation.

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