Laser Photoacoustic Spectroscopy Research Articles

Exploring the potential of laser photoacoustic spectroscopy (LPAS) for predicting amylose content in rice flour

Exploring the potential of laser photoacoustic spectroscopy (LPAS) for predicting amylose content in rice flour

Temporal Variations in Urban Air Pollution during a 2021 Field Campaign: A Case Study of Ethylene, Benzene, Toluene, and Ozone Levels in Southern Romania

This study focused on quantifying the gas concentrations of ethylene, benzene, toluene, and ozone within an urban area in the southern region of Romania. The gas sampling campaign, conducted between March and August 2021, took place in three different locations from the point of view of the architectural structure, and the sampling height was 1.5 m. Sampling occurred on weekdays (Monday through Friday) during daylight hours, with subsequent concentration analysis employing descriptive statistics, diurnal cycles, and seasonal assessments. A highly sensitive and selective detector, employing laser photoacoustic spectroscopy, was utilized to monitor pollutants. The average concentrations (±Standard Deviation) were determined as follows: ethylene at 116.82 ± 82.37 parts per billion (ppb), benzene at 1.13 ± 0.32 ppb, toluene at 5.48 ± 3.27 ppb, and ozone at 154.75 ± 68.02 ppb, with peak levels observed during the summer months. Diurnal patterns were observable for ethylene, benzene, and toluene, exhibiting higher concentrations during the early hours of the day followed by a decrease towards the evening. In contrast, ozone concentrations peaked in the evening compared to the early part of the day. Thus, perceptible effects were demonstrated on gas concentrations as a result of the influence of meteorological variables. Moreover, the high toluene/benzene ratio indicated traffic and industrial emissions as primary sources of these pollutants. Of the four gases monitored, benzene and ozone exceeded regulatory limits, particularly during the summer season, highlighting concerns regarding air quality in the studied urban environment.

Urban Air Pollution by Laser Photoacoustic Spectroscopy and Simplified Numerical Modeling of Gas Pollution in Urban Canyon

With rapid urbanization and industrialization, atmospheric pollution has emerged as a significant environmental challenge in Romania. Employing a laser photoacoustic spectroscopy detector, researchers analyzed ethylene, benzene, and toluene simultaneously across three distinct environmental settings in the country's southern region. This investigation spanned from March to August 2021, covering both spring and summer seasons. Measurements were taken at a breathing height of 1.5 meters above ground level. The highest concentrations of ethylene (116.82 ± 82.37 ppb), benzene (1.13 ± 0.32 ppb), and toluene (5.48 ± 3.27 ppb) were recorded at measurement point P1, situated within the city amidst residential buildings during the summer season. Additionally, the highest ozone levels (154.75 ± 68.02 ppb) were observed at point P3, located in an industrial area, during the summer. The behavior of gas concentrations is influenced by meteorological factors such as temperature, wind speed, and direction. The high toluene/benzene ratio suggests that traffic and industrial emissions are the primary sources of these pollutants. Notably, benzene and ozone concentrations exceeded prescribed limit values based on the measurements. Concurrently, a numerical model was employed to assess the impact of greenery on mitigating pollution in urban canyons. Specifically, the study focused on how wind velocity affects the dispersion of benzene pollutants in a street canyon. This study's governing equations utilized for air pollutant flow were the Reynolds-averaged Navier–Stokes (RANS) equations for compressible turbulent flow and moisture transport in air, implemented through Comsol software.

Infrared to terahertz identification of chemical substances used for the production of IEDs

In our modern times, improvised explosive devices (IEDs) have become more sophisticated than ever, capable of causing destruction and loss of life. The creative use of homemade substances for IEDs manufactures has led to efforts in developing sensitive detection methods that can anticipate, identify and protect against improvised attacks. Laser-based spectroscopic techniques provide rapid and accurate detection of chemicals in improvised explosives, but no single method can detect all components of all explosives. In this study, two spectroscopic methods are used for the sensitive identification of 8 explosive chemical substances in the form of powders and vapors. Absorption spectra of benzene, toluene, acetone and ethylene glycol were examined with CO2 laser photoacoustic spectroscopy. The photoacoustic signals of the samples were recorded in the CO2 laser emission range from 9.2 to 10.8 µm and a different spectral behavior was observed for each analyzed substance. Time-domain spectroscopy with THz radiation was used to analyze ammonium nitrate, potassium chlorate, dinitrobenzene, hexamethylenetetramine transmission spectra in the 0.1–3 THz range, and it was observed that they have characteristic THz fingerprint spectra. CO2 laser photoacoustic spectroscopy and THz time domain spectroscopy have met the criterion of proven effectiveness in identifying explosive components. The combination of these spectroscopic methods is innovative, giving a promising new approach for detection of a large number of IED components.

SO2 and SOF2 gas mixture detection by mid-infrared laser photoacoustic spectroscopy based on IWOA-BP

SO₂ and SOF₂ gas mixture detection by mid-infrared laser photoacoustic spectroscopy based on IWOA-BP

Rapid Non-Contact Detection of Chemical Warfare Agents by Laser Photoacoustic Spectroscopy.

Nerve agents have recently been used in battlefield operations, espionage wars, and terrorist attacks. These compounds, like some pesticides, cause organophosphate poisoning. The rapid, noncontact detection of a sarin simulant in the liquid phase has been demonstrated at the Diagnostics and Metrology Laboratory of the Italian National Agency for New Technologies, Energy and Sustainable Economic Development using laser photoacoustic spectroscopy, an infrared absorption technology. The first measurements, carried out with an experimental system based on a quantum cascade laser and developed for the assessment of food authenticity in the "fingerprint region", show that a detection limit of one nanolitre is within the reach of the instrument when chemometric analysis is applied.

Identification of Absorption Spectrum for IED Precursors Using Laser Photoacoustic Spectroscopy.

Among the many commonly encountered hazards, improvised explosive devices (IEDs) remain the primary threat to military and civilian personnel due to the ease of their production and the widespread availability of their raw materials and precursors. Identifying traces of potential precursors is the first step in developing appropriate control measures. An interesting approach is to identify the precursors that are released around the site as they are handled and transformed into the final IEDs. CO2 laser photoacoustic spectroscopy can offer the spectral characterization of a number of explosives-related compounds without sample preparation. Benzene, toluene, acetone, and ethylene glycol absorption spectra were determined in the IR region between 9.2 and 10.8 µm. Each substance emitted a unique photoacoustic response corresponding to its chemical composition that could be further used to identify the explosive material.

Oregano herb adulteration detection through rapid spectroscopic approaches: Fourier transform-near infrared and laser photoacoustic spectroscopy facilities

Oregano is a culinary herb known and used worldwide, whose demand and cost encourage illegal activities in terms of fraud, especially adulteration. The scope of this study is to provide a rapid, cost-effective and easy-to-use approach to detect the adulteration of oregano with a common matrix, the olive leaves. Two analytical solutions were considered, Fourier transform near infrared (FT-NIR), using two different instruments, and laser photoacoustic spectroscopy (LPAS). Different raw data preprocessing procedures were applied, Principal Component Analysis (PCA) was used for preliminary data visualisation, while Partial Least Squares Regression (PLS-R) and Discriminant Analysis (PLS-DA) allowed the authors to classify samples with different adulteration percentages. FT-NIR performed better than LPAS, perhaps also because the photoacoustic system is still an experimental prototype. For example, the coefficient of determination R2 between actual and predicted adulterant concentrations was in the range 0.93–1.00 for FT-NIR and in the range 0.86–0.96 for LPAS. Nevertheless, this allowed the use of a low level data fusion approach to increase the consistency of the statistical model. The fusion between raw data from the LPAS prototype and one of the FT-NIR instruments gave optimal results, confirming the potential of these analytical solutions for the identification of oregano adulterants. The approaches used in the present work could be applied to the identification of other adulterants in herbs and spices by food companies for quality control measurements, possibly for on line and in field analysis.

Quartz-Enhanced Photoacoustic Spectroscopy in the Terahertz Spectral Range

Infrared laser photo-acoustic spectroscopy provides very high sensitivity of a gas sample analysis when high-power tunable laser radiation sources and resonant photo-acoustic detectors (PADs) are used. In the resonant PAD, the acoustic signal generated by absorbed laser radiation in a measurement chamber is amplified proportionally to a Q-factor of the acoustic resonator. But, compact tunable high-power lasers (with power above 100 mW) still are not widely spread in the terahertz spectral range. One of the ways to achieve an acceptable sensitivity of terahertz photo-acoustic spectroscopy is using PADs with a very high Q-factor. The latter can be achieved using PAD with a quartz tuning fork. The current state in this field is presented in the review.

NIR and THz spectroscopy: An experimental investigation toward nicotine-related devices.

This study examined the content of nicotine-delivery products using terahertz time-domain spectroscopy (THz-TDS) and breath ethylene investigated with CO2 laser photoacoustic spectroscopy (CO2 LPAS) system as a biomarker of oxidative stress after smoking. The THz-TDS method provided valuable information on the transmission spectra of tobacco and nicotine in smoking products. From the CO2 LPAS data it was observed that in cigarette (TC) smoking the mean breath ethylene was 687 parts per billion (ppb), while in electronic cigarettes and tobacco heating devices smoking the mean ethylene was 56 ppb and 48 ppb, respectively. The main finding was that TC showed higher transmission in the THz region producing a higher oxidative stress on the body.

Optical Methods of Methane Detection.

Methane is the most frequently analyzed gas with different concentrations ranging from single ppm or ppb to 100%. There are a wide range of applications for gas sensors including urban uses, industrial uses, rural measurements, and environment monitoring. The most important applications include the measurement of anthropogenic greenhouse gases in the atmosphere and methane leak detection. In this review, we discuss common optical methods used for detecting methane such as non-dispersive infrared (NIR) technology, direct tunable diode spectroscopy (TDLS), cavity ring-down spectroscopy (CRDS), cavity-enhanced absorption spectroscopy (CEAS), lidar techniques, and laser photoacoustic spectroscopy. We also present our own designs of laser methane analyzers for various applications (DIAL, TDLS, NIR).

High-Sensitivity Multitrace Gas Simultaneous Detection Based on an All-Optical Miniaturized Photoacoustic Sensor.

We propose an all-optical miniaturized multigas simultaneous detection photoacoustic (PA) sensor, which is primarily composed of a copper tube, a silica cantilever, and four single-mode fibers. Three single-mode fibers are used as excitation fibers to transmit lasers of different wavelengths, and the remaining one is used as a probe fiber. The volumes of the PA cell (PAC) and the sensor are 36 μL and 71 cubic millimeters, respectively. A laser photoacoustic spectroscopy (PAS) system, using the all-optical miniaturized PA sensor as a detector, 1532.8, 1576.3, and 1653.7 nm distributed feedback (DFB) lasers as the excitation sources for acetylene (C2H2), hydrogen sulfide (H2S), and methane (CH4) gases, and a high-speed spectrometer as a demodulator, has been developed for multigas simultaneous measurements. The minimum detection limits of 4.8, 162, and 16.6 parts per billion (ppb) have been achieved for C2H2, H2S, and CH4, respectively, with an integration time of 100 s. The reported sensor shows a potential for high-sensitivity multigas simultaneous measurements in cubic millimeter-scale space.

Monitoring of ammonia concentrations from coir-husk litter of Brazilian poultry house using diode laser photoacoustic spectroscopy.

Ammonia (NH_3) from manure is a concern in raising broiler due to possible damages to production and the environment. Brazil is the main exporter of chicken meat in the world and is also responsible for large waste of poultry litter. The country, likewise, figures as top 5 producers of green coconut, which results in considerable volumes of waste, since 80%-85% of the fruit is unusable. This work analyzes the ammonia concentration profile of two bedding substrates for raising broiler, to know, coir-husk fiber and a commonly used pine wood shavings in a Brazilian climate. A differential home-made photoacoustic cell combined with a diode laser was employed for sensing ammonia at trace levels. Such combination confers selectivity as well as lower limits of detection to the system. The chemical compositions pH, N, C, Ca, Mg, P_2O_5 and K_2O were also determined, in addition to the moisture, dry matter and mineral content of substrates and litters. NH_3 concentrations varied from (0.9 ± 0.3) ppmv to (19 ± 3) ppmv and from (2.1 ± 0.5) ppmv to (21 ± 3) ppmv for the coir-husk fiber and wood shavings substrates, respectively. Results showed the feasibility of using coconut fiber as poultry litter in regions where this material is a common waste. Moreover, as NH_3 concentrations were lower for coconut fiber bedding compared to shavings, this coir-husk fiber is a potential residue to guarantee the environmental sustainability by Brazilian poultry farming. Coir-husk fibers presented significantly higher amounts of P and K in comparison to pine wood. NH_3 profiles revealed that coir-husk fiber emitted lower quantities than wood shavings. Besides, a delay on the NH_3 emission pattern was clearly seen when the coconut waste was the bedding material. Such a tendency was confirmed by the logistic model. Our findings, in turn, make the coir-husk an environmentally friendly alternative low-cost product for poultry litter as well as its potential use as natural fertilizer. The later deserves attention since there is a need to accurately assess the emissions of methane, nitrous oxide, and carbon dioxide during the composting process. In Brazil, the waste generated by the high production of green coconut is an environmental liability. The cost of poultry production has been high, reducing the profit of producers, who seek to make production cheaper. Measuring NH_3 from poultry activity in Brazil, a tropical country, aims to control management and reduce production losses, since NH_3 is a harmful gas to birds. The measurement of NH_3 concentrations at trace levels from raising broilers by photoacoustic diode laser spectroscopy, to the best of our knowledge, has been reported for the very first time.

Ammonia Concentration in Ambient Air in a Peri-Urban Area Using a Laser Photoacoustic Spectroscopy Detector.

Measuring ammonia from the environmental air is a sensitive and prioritized issue due to its harmful effects on humans, ecosystems, and climate. Ammonia is an environmental pollutant that has an important role in forming secondary inorganic aerosols, the main component of fine particulate matter concentrations in the urban atmosphere. Through this study, we present a gas analyzer that utilizes the technique of laser photoacoustic spectroscopy to measure ammonia concentration in three different sites located in Magurele, (44°20′58″ N 26°01′47″ E, 93 m altitude), Romania, from March to August 2021 at the breathing level of 1.5 m above ground. The ammonia concentrations from the ambient air were elevated in summer (mean of 46.03 ± 8.05 ppb (parts per billion)) compared to those measured in spring (18.62 ± 2.92 ppb), which means that atmospheric temperature affects ammonia concentrations. The highest mean ammonia concentrations occurred in August, with an ammonia concentration level of 100.68 ± 11.12 ppb, and the low mean ammonia concentrations occurred in March, with an ammonia level concentration of 0.161 ± 0.03 ppb. The results confirm that meteorological characteristics (i.e., temperature) and motor vehicles are major contributors to the elevated ammonia levels during the monitoring period.

Detection of SF 6 decomposition components SO 2 F 2 and SOF 2 based on mid-infrared laser photoacoustic spectroscopy

Detection of SF ₆ decomposition components SO ₂ F ₂ and SOF ₂ based on mid-infrared laser photoacoustic spectroscopy

Alfalfa (Medicago sativa) Sprouts Respiratory Responses to Cadmium Stress Using IR LPAS

Cadmium (Cd) is not considered a fundamental element for plants inducing general growth disturbances and inhibition in many species of plants. The purpose of our research was to examine the ethylene (C2H4) and ammonia (NH3), emissions in alfalfa sprouts with or without Cd, using infrared laser photoacoustic spectroscopy (IR LPAS), in order to suggest new markers that may add a better knowledge of Cd effect. The responses of alfalfa sprouts to C2H4 and NH3 may fluctuate, depending on tissue sensitivity and the phase of plant development. From the determinations of this study, the C2H4 was established to be inhibited, while NH3 was established to be in a higher concentration with the amount of Cd added to the alfalfa seeds for growth when the values were correlated to the control and BIOalfalfa sprouts (Sonnentor).

Quantum Cascade Laser Photoacoustic Spectroscopy Applied to Rice Flour Analysis

In the present work we applied laser photoacoustic spectroscopy (LPAS) to the analysis of food samples. In particular, we analyzed samples of different rice flours (standard and commercial ones). For this purpose, a laboratory system based on quantum cascade laser (QCL) has been developed and characterized. After that, the LPAS spectra of all the rice samples were collected with a standard error of less than 2% of the measured value and a background signal negligible compared to the sample signals. All the experimental LPAS spectra resulted to be rich in spectral features showing clear differences between each other. The experimental spectra were then analyzed by comparison with the FT-IR transition frequency recorded in our laboratory to consent a proper assignment. Finally, to put in evidence the small differences among the various rice types, the Principal Component Analysis (PCA) was applied to the recorded LPAS spectra highlighting five different groups corresponding to the five types of samples. In conclusion, the present work demonstrated the discriminating capability of LPAS technique in the case of different types of rice flour samples.

Ppb level detection of carbonyl sulfide and ethene and study resonant frequencies using laser photoacoustic spectroscopy

AbstractLaser photoacoustic spectroscopy is a laser measurement method with high sensitivity, good selectivity, nondestructive, and fast response (real‐time). In the present work, to detect carbonyl sulfide and ethene gases and measure resonant frequencies and signals, the photoacoustic spectroscopy system was designed and set up. The detection limit of this system to trace ethene and carbonyl sulfide was measured 3 ppb and 8 ppb, respectively. Also, for these two gases at the presence of different buffer gases, the resonant frequency and photoacoustic signal were recorded. The results showed that among the used buffer gases, xenon has the best acoustic performance and gives the highest photoacoustic signal. The signal also increased with increasing pressure of buffer gas, because increasing the pressure leads to improved collisional processes. The study of resonant frequencies of this system for these two gases in the presence of buffer gases showed that with increasing the pressure of xenon, argon, and nitrogen buffer gases from 65 to 765 Torr, the resonant frequency does not change significantly. But in the case of helium buffer gas, these resonant frequency changes are significant, and as the helium pressure increases by 65 to 765 Torr, the resonant frequencies of carbonyl sulfide and ethene change from 2016 to 2630 Hz and from 2100 to 2740 Hz, respectively. The reason for the different behavior of helium is the higher speed of sound in helium than in other buffer gases.

PREDIKSI CEPAT KUALITAS AIR MENGGUNAKAN LPAS (LASER PHOTO-ACOUSTIC SPECTROSCOPY) DENGAN MENERAPKAN METODE KOREKSI CUTTING EDGE FILTERING

A tool that can predict water quality by capturing sound vibrations generated by collisions between water samples and light is LPAS (Laser Photo-Acoustic Spectroscopy). To process the data acquired by LPAS, spectrum correction is needed to eliminate data errors when making acquisitions on water samples. The correction method used in this research is the cutting edge filtering correction method. The regression model that can be used is the PLSR (Partial Least Square Regression) regression model. This research was conducted in the Instrumentation and Energy Laboratory, Agricultural Engineering Study Program, Faculty of Agriculture, Syiah Kuala University. Water sample analysis was carried out at the Laboratory of the Industrial Research and Standardization Center (BARISTAND) Banda Aceh. This study used 4 monitoring wells within the TPA (Final Disposal Site) and 4 samples were taken from community wells outside the scope of TPA Gampong Jawa, Banda Aceh City. The results of this study indicate the parameters (temperature, turbidity, Ph, TSS, DO, BOD and Nitrate) are predicted to be in the frequency range 4000 - 10,000 cm-1. Raw spectrum data for pH and Nitrate (NO3-) parameters produce better data than the spectrum data for cutting edge filtering correction methods while cutting edge filtering spectrum data for temperature, turbidity, TSS, DO and BOD-5 parameters are better than spectrum raw data. This study also shows that the cutting edge filtering correction method is able to cut boundaries and compress the spectrum so that it can provide data limits on the spectrum so that the PLSR method can be applied to predict water quality. Keywords: water quality; Laser Photo-Acoustic Spectroscopy, correction method, regression method

Portable ppb-level acetylene photoacoustic sensor for transformer on-field measurement

Acetylene (C2H2) is considered as one of the typical decomposition gas of transformer oil to measure the severity of oil-immersed transformer fault. Quantitative measurement of trace C2H2, especially on-field measurement, has long been the center of fault diagnosis field. In this work, a ppb-level photoacoustic sensor for C2H2 was developed for transformer insulation status detection. Firstly, combined degassing method was employed to extract dissolved gas from oil. According to known Ostwald coefficient at certain temperature, the concentration of dissolved C2H2 in oil can be calculated by measuring the concentration of extracted C2H2. Then, a quantitative detection system for C2H2 based on laser photoacoustic spectroscopy was established in this work. The concentration of the extracted C2H2 can be reversed by obtained photoacoustic signal. Experimental results indicate that the detection limit of proposed system can reach ~3.4 ppb. Besides, compared with the quantitative detection results of GC, the relative error of proposed sensor could meet relevant requirements. Experimental fruitions testify the feasibility of proposed sensor for field application, and the results of this work may serve as a guide of insulation fault diagnosis for oil-immersed transformer.