Water-based enhancement of the resonant photoacoustic signal from methane–air samples excited at 3.3 μm

Barreiro, N. L.; Peuriot, A.; Santiago, Guillermo; Slezak, V.

doi:10.1007/s00340-012-5018-5

Cited by 24 publications

(22 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The effect of the CH 4 relaxation in O 2 has been presented in [13] in the case of near-infrared detection of methane with a line excitation of 2ν 3 band at 1.65 µm. The effect of CH 4 relaxation in O 2 [14] and the effect of water vapor [15] have also been presented in the case of an excitation in the ν 3 band at 3.3 µm. All the effects described therein are related to the coupling between ν 2 and ν 4 bands of methane and either the first vibrational state of oxygen or the ν 2 vibrational level of H 2 O.…”

Section: Flow Measurement and Calibrationmentioning

confidence: 97%

Optimization and complete characterization of a photoacoustic gas detector

et al. 2014

View full text Add to dashboard Cite

periodically modulated in and out an absorption line of the studied molecule. During the relaxation process, energy is mainly transferred by collision to the surrounding molecules. A local change of temperature is then induced along the laser beam, and a standing wave is created inside the cell.Photoacoustic cells are often used in resonant mode in order to take advantage of the enhancement of the acoustical signal. The resonator shape directly affects the strength and the distribution of these pressure variations. To take full benefits of the sound wave amplification, the quality factor, the resonant frequency and the peak amplitude at resonance are the three main parameters to be determined. These three parameters are usually experimentally determined from the cell response:U is the measured voltage of the microphone (V), R M its sensitivity (V/Pa), W the optical power of the laser (W), c the gas concentration and K the absorption coefficient (cm −1 ). The maximum value of R c (ω) is often referred as the cell constant. This constant is used to determine the detection limit of the photoacoustic spectrometer. In order to enhance this detection limit, one must be able to predict the cell response.Positions of resonant frequencies and Q-factors can be calculated for simple resonant volume where analytic solution exists [2]. For more complex cells, electric analogy can also be used to investigate the cell response [3]. Finite element method (FEM) presents the ease of use of a computational calculation and has already demonstrated its capabilities for the simulation of the photoacoustic cell characteristics. Baumann et al. [4] predicted the resonant frequencies and Q-factors of a T-shaped cell with a goodAbstract We report the complete designing process and realization of a photoacoustic spectrometer. In a first step, the cell design is optimized in order to achieve maximum cell constant and working frequency using a finite element method. Technological and integration constraints are used to define dimensional constraints on the cell. In a second step, a dedicated optical bench is presented along with the photoacoustic cell. The resonator response is then measured using a quantum cascade laser for methane detection and condenser microphones as detectors. The system detection limit is also discussed as it depends not only on the cell response but is also a combination of parameters linked together: environmental noise, microphones characteristics and cell conception. The gas flow required in a dynamic operation of the sensor degrades the detection limit regardless of the microphones quality. Choices on cell conception to minimize gas flow noise are discussed.

show abstract

Section: Flow Measurement and Calibrationmentioning

confidence: 97%

Optimization and complete characterization of a photoacoustic gas detector

et al. 2014

View full text Add to dashboard Cite

show abstract

“…Considerando la baja presión necesaria para alcanzar a liberar la mayoría de la energía absorbida por el metano, es posible distinguir cuál de los procesos mencionados anteriormente debería primar frente a los demás. Gregory V et al (8) han mostrado que para moléculas grandes como compañeras colisionantes, como es el caso del SF6, las transferencias V-V suelen dominar frente a las V-T descartando los procesos (4) y (5) frente a (2) y (6). Para conocer si la energía se transfiere por (2) o (6) es posible estimar las tasas de transferencia en cada caso.…”

Section: Transferenciaunclassified

“…Los intercambios V-V entre metano-oxígeno (1) se dan con una tasa de k = 2,6 10 5 s -1 Torr -1 (4) , siendo éste un valor típico para este tipo de interacciones. Si se asume que el proceso (6) ocurre con una tasa k del mismo orden de magnitud, se puede estimar el tiempo V-V de ocurrencia de los procesos (1) y (6) como 2 1 O N k y 6 1 SF N k siendo N(O2) y N(SF6) las poblaciones de ambas moléculas en el estado fundamental. De este modo se puede observar que el tiempo requerido para (1) es menor que para (6) ya que en aire a presión atmosférica la presión de oxígeno es alrededor de 152 Torr y la presión de SF6 considerada es de 10 Torr.…”

Section: Transferenciaunclassified

“…Dado el interés de monitorear metano en aire atmosférico, es importante lograr que el límite de detección sea el adecuado, para lo cual hay que incrementar la sensibilidad de la técnica. Algunos autores (4,6) han mostrado que, en estos casos, la adición de un compañero colisional del oxígeno o el metano puede incrementar la señal hasta alcanzar el valor del caso metano-nitrógeno. En este trabajo se propone el uso de hexafloruro de azufre (SF6), un gas inerte y no absorbente en la región de 3000 cm -1 , el cual es comúnmente utilizado para relajación colisional de otros gases (7,8) debido a su alta densidad de niveles vibracionales en la región del infrarrojo medio.…”

Section: Introductionunclassified

See 1 more Smart Citation

Increase of the Resonant Photoacoustic Signal of Methane in Air Adding Sulphur Hexafluoride

Falcione¹,

Barreiro²,

Slezak³

et al. 2013

AnAFA

View full text Add to dashboard Cite

R e c i b i d o : 1 4 / 1 2 / 1 2 ; A c e p t a d o : 0 2 / 0 5 / 1 3 En este trabajo se estudia la técnica fotoacústica resonante aplicada a la detección de metano. Para realizar la medición se utilizó una celda que presenta un resonador cilíndrico con filtros de cuarto de onda, silenciadores regulables y ventanas en ángulo de Brewster. La excitación se realizó en doble pasaje con un oscilador parametrico óptico modulado. La adquisición se efectuó en forma sincrónica con un amplificador lock-in cuya referencia provenía del modulador mecánico. En trabajos anteriores, se ha encontrado que la señal fotoacústica de metano en una atmósfera de aire es menor que la medida en una atmósfera de nitrógeno puro. Esto se debe a que, luego de un fuerte intercambio de energía entre niveles resonantes del oxígeno y el metano, la energía se acumula en un nivel metaestable del oxígeno (1500 cm -1 ) en lugar de convertirse en energía cinética. En este trabajo se revierte este proceso mediante el agregado de un par colisional del oxígeno: el hexafloruro de azufre. Esta molécula, que presenta alta densidad de niveles vibracionales alrededor de 1500 cm -1 , colisiona con el oxígeno y el metano dando lugar a un fuerte intercambio, que permite liberar la energía a cinética, incrementando la señal fotoacústica. Palabras Claves: Fotoacústica, metano, hexafloruro de azufreIn this paper we study the resonant photoacoustic technique applied to the detection of methane. A cell was used which consists of a cylindrical resonator, quarter wave filters, adjustable buffer volume and Brewster angle windows. The excitation was performed in double passage with a modulated optical parametric oscillator. The acquisition was synchronous with a lock-in amplifier whose reference came from the mechanical modulator. In previous work, we have found that the photoacoustic signal of methane in air is less than in pure nitrogen.. This is because, after a strong energy exchange between resonant levels of oxygen and methane, energy is accumulated in a metastable level of oxygen (1500 cm -1 ) instead of being converted into kinetic energy. In this work this process goes back by adding a collisional partner to oxygen: sulphur hexafluoride. This molecule, which shows high density of vibrational levels around 1500 cm -1 , collides with the oxygen and methane molecules, resulting in a strong exchange which enables a kinetic energy release, which causes an increase of the photoacoustic signal. I. INTRODUCCIÓNEl metano (CH4), gas de efecto invernadero de similar impacto al dióxido de carbono, presenta una concentración de alrededor de 1,7 ppmV en la atmósfera. Este valor fue alcanzado debido a un acelerado incremento en los últimos 150 años vinculado a las múltiples fuentes emisoras tanto naturales como antropogénicas (1,2) . Por este motivo, el monitoreo de las emisiones de metano es de gran importancia para mantener un control sobre las mismas. En este trabajo, se propone el uso de la espectroscopia fotoacústica (FA) para la detección de metano ya que presenta gran s...

show abstract

“…Water vapor is utilized as a highly efficient promoter for vibrational-translational (V-T or thermal) collisional relaxation [18], also acting as a promoter in the V-T relaxation of O 2 (1) [17]. Water is either added to maximize the photoacoustic response [4,17,19], or measured simultaneously, to correct for changing overall relaxation times [5]. However, the H 2 O molecule itself has a near-resonant V-V coupling of the first bending mode, H 2 O( 1 = 0 , 2 = 1 , 3 = 0 ) ( 1595 cm −1 ), with O 2 (1), with an energy transfer more efficient than the thermal relaxation by the major atmospheric constituents O 2 and N 2 [20,21].…”

Section: Introductionmentioning

confidence: 99%

Molecular relaxation effects on vibrational water vapor photoacoustic spectroscopy in air

et al. 2020

View full text Add to dashboard Cite

Photoacoustic spectroscopy is a highly sensitive technique, well suited for and used in applications targeting the accurate measurement of water vapor in a wide range of concentrations. This work demonstrates the nonlinear photoacoustic response obtained for water vapor in air at typical atmospheric concentration levels, which is a result of the resonant vibrational coupling of water and oxygen. Relevant processes in the relaxation path of water in a mixture with air, excited with nearinfrared radiation, are identified and a physical model for the acoustic signal measured with a resonant photoacoustic cell is presented. The model is valid for modulation frequencies typical for conventional and quartz-enhanced photoacoustic spectroscopy and provides a simplified means of calibration for photoacoustic water vapor sensors. Estimated values for comprised model coefficients are evaluated from photoacoustic measurements of water vapor in synthetic air. Furthermore, it is shown experimentally that the process of vibrational excitation of nitrogen is of negligible importance in the relaxation path of water vapor and thus insignificant in the photoacoustic heat production in atmospheric measurement environments.

show abstract

Water-based enhancement of the resonant photoacoustic signal from methane–air samples excited at 3.3 μm

Cited by 24 publications

References 21 publications

Optimization and complete characterization of a photoacoustic gas detector

Optimization and complete characterization of a photoacoustic gas detector

Increase of the Resonant Photoacoustic Signal of Methane in Air Adding Sulphur Hexafluoride

Molecular relaxation effects on vibrational water vapor photoacoustic spectroscopy in air

Contact Info

Product

Resources

About