Photoacoustic Analysis Research Articles

Ammonia and Greenhouse Gas Flux from Manure in Freestall Barn with Dairy Cows on Precision Fed Rations

Two lactating cow trials were conducted to evaluate the impact of diets differing in silage source (alfalfa/maize vs. grass/maize or maize/hay) and maize grain particle size (fine vs. coarse) on ammonia (NH3), carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions from a freestall barn floor with two groups of 60 cows each. In addition, the effects of environment (temperature, humidity) and management (manure depth, time since manure removal) factors were evaluated. Manure (feces and urine), spilled feed, bedding, and spilled drinking water were allowed to collect on the solid concrete, sloped barn alleys and were scraped twice a day. Gas fluxes from the freestall floor were measured at 64 locations over a 12 h period using a fast-response, non-steady-state flux chamber and an infrared photoacoustic gas analyzer during 18 trial days over a 9-month period. Fluxes of ammonia from manure on the barn floor were within average reported values for these 165 g kg-1 crude protein diets. All gas fluxes were similar (p = 0.253 to 0.977) regardless of silage source and maize grain particle size. The highest average ammonia emissions coincided with higher environmental temperature at 30 NH3 g AU-1 d-1, while the highest average greenhouse gas emissions from the manure on the floor were 10 g AU-1 d-1 for CH4 and 580 g AU-1 d-1 for CO2. Time in hours since scraping the floor had little impact on the production of ammonia, but greenhouse gas loss from the barn floor was reduced after scraping. Air and manure temperatures were positively correlated with emissions of NH3, CO2, and CH4 (p = <0.0001). NH3 (g AU-1 d-1) = (R2 = 0.38) for indoor air temperatures (Tair, C) over the range from -5C to 32C (AU = 500 kg animal unit). Ammonia emissions were positively correlated with CO2 and CH4 gas emissions, suggesting that NH3 release from the manure was controlled to some extent by microbial activity and similar environmental factors. Nitrous oxide emissions remained <0.1 g AU-1 d-1 and were relatively constant for all diets and trials.

Investigation of the Desorption Process in UV Matrix-Assisted Laser Desorption/Ionization with a Liquid 3-Nitrobenzyl Alcohol Matrix by Photoacoustic Analysis, Fast-Flash Imaging, and UV-Laser Postionization

Ultraviolet matrix-assisted laser desorption/ionization mass spectrometry (UV-MALDI-MS) is a widely used method for the analysis of a variety of biomolecules. The technique relies on the codesorpti...

Thermal and optical properties of Cd2SnO4 thin films using photoacoustic spectroscopy

Cadmium stannate (Cd2SnO4) thin films were prepared by the RF magnetron sputtering technique on glass substrates with substrate temperatures of room temperature (RT), 100°C, 200°C and 300°C. Photoacoustic analyses were made to obtain the thermal diffusivity and the optical bandgap values of the Cd2SnO4 thin films. The change in thermal diffusivity of the films with the substrate temperature was analyzed. The optical bandgap values obtained from the photoacoustic spectroscopy were compared with the values obtained from the optical transmittance spectra. X-ray photoelectron spectroscopic (XPS) studies confirm the formation of stoichiometric films. Surface morphological studies by atomic force microscopy (AFM) revealed the crystalline nature of the films deposited at 100°C.

Development of a visible-light-responsive titania nanotube photocatalyst by site-selective modification with hetero metal ions

A titania nanotube (TNT), which was obtained by calcinations of a titanate nanotube, was modified with two kinds of transition metal ions, iron(III) (Fe3+) and zinc(II) (Zn2+) ions. TNT with site-selective modification with metal ions showed higher photocatalytic activity than that of bare TNT, presumably due to separation of redox sites, and oxidation on the outside surface and reduction on the inside surface were the preferable separated redox sites on the tubular structure for decomposition of acetaldehyde. Modification of TNT with Fe3+ ions induced improvement of photocatalytic activity under visible-light irradiation as well as ultraviolet (UV) irradiation. On the other hand, TNT modified with Zn2+ ions showed the largest enhancement of photocatalytic activity under UV irradiation, though increase in visible-light activity was hardly observed. Double-beam photoacoustic spectroscopic analyses indicated that Zn2+ ion works efficiently as an electron acceptor, while Fe3+ ion is an effective sensitizer for visible light.

X-ray diffraction, Raman, and photoacoustic studies of ZnTe nanocrystals

Nanocrystalline ZnTe was prepared by mechanical alloying. X-ray diffraction (XRD), energy dispersive spectroscopy, Raman spectroscopy, and photoacoustic absorption spectroscopy techniques were used to study the structural, chemical, optical, and thermal properties of the as-milled powder. An annealing of the mechanical alloyed sample at 590 °C for 6 h was done to investigate the optical properties in a defect-free sample (close to bulk form). The main crystalline phase formed was the zinc-blende ZnTe, but residual trigonal tellurium and hexagonal ZnO phases were also observed for both as-milled and annealed samples. The structural parameters, phase fractions, average crystallite sizes, and microstrains of all crystalline phases were obtained from Rietveld analyses of the X-ray patterns. Raman results corroborate the XRD results, showing the longitudinal optical phonons of ZnTe (even at third order) and those modes of trigonal Te. Nonradiative surface recombination and thermal bending heat transfer mechanisms were proposed from photoacoustic analysis. An increase in effective thermal diffusivity coefficient was observed after annealing and the carrier diffusion coefficient, the surface recombination velocity, and the recombination time parameters remained the same.

Mass Absorption Cross-Section of Ambient Black Carbon Aerosol in Relation to Chemical Age

Three differing techniques were used to measure ambient black carbon (BC) aerosols in downtown Toronto through 20 December 2006 to 23 January 2007. These techniques were thermal analysis, as performed by a Sunset Labs OCEC Analyzer (OCEC); light attenuation, as performed by an Aethalometer (AE); and photoacoustic analysis, as performed by a Photoacoustic Instrument (PA). These measurements of ambient PM 2.5 were used to investigate the effects of coating thickness on BC Mass Absorption Cross-section (MAC). MAC values were determined by comparing 880 nm and 370 nm AE measurements and PA measurements of b abs (absorption coefficient, Mm–1) to the OCEC measurements. Based on mass size distributions and supporting criteria, the PM 2.5 was classified as fresh, semi-aged, or aged. The average MAC values in these categories, based on the PA measurements, were 9.3 ± 1.8, 9.9 ± 2.0, and 9.3 ± 2.2 m 2 /g (mean ± standard deviation), respectively, suggesting that any difference in coating thickness as a result of ag...

Aerosol light absorption, black carbon, and elemental carbon at the Fresno Supersite, California

Particle light absorption ( b ap), black carbon (BC), and elemental carbon (EC) measurements at the Fresno Supersite during the summer of 2005 were compared to examine the equivalency of current techniques, evaluate filter-based b ap correction methods, and determine the EC mass absorption efficiency (σ ap) and the spectral dependence of b ap. The photoacoustic analyzer (PA) was used as a benchmark for in-situ b ap. Most b ap measurement techniques were well correlated ( r ≥ 0.95). Unadjusted Aethalometer (AE) and Particle Soot Absorption Photometer (PSAP) b ap were up to seven times higher than PA b ap at similar wavelengths because of absorption enhancement by backscattering and multiple scattering. Applying published algorithms to correct for these effects reduced the differences to 24 and 17% for the AE and PSAP, respectively, at 532 nm. The Multi-Angle Absorption Photometer (MAAP), which accounts for backscattering effects, overestimated b ap relative to the PA by 51%. BC concentrations determined by the AE, MAAP, and Sunset Laboratory semi-continuous carbon analyzer were also highly correlated ( r ≥ 0.93) but differed by up to 57%. EC measured with the IMPROVE/STN thermal/optical protocols, and the French two-step thermal protocol agreed to within 29%. Absorption efficiencies determined from PA b ap and EC measured with different analytical protocols averaged 7.9 ± 1.5, 5.4 ± 1.1, and 2.8 ± 0.6 m 2/g at 532, 670, and 1047 nm, respectively. The Angström exponent (α) determined from adjusted AE and PA b ap ranged from 1.19 to 1.46. The largest values of α occurred during the afternoon hours when the organic fraction of total carbon was highest. Significant biases associated with filter-based measurements of b ap, BC, and EC are method-specific. Correcting for these biases must take into account differences in aerosol concentration, composition, and sources.

Photoacoustic analysis of CO2 content in annual tree rings

We have used laser photoacoustic gas analysis to study the CO2 content sorbed by the capillary porous system of annual rings in cross-sectional disks of some conifers. The measurement results showed that in most cases, the CO2 content in gas samples extracted by the vacuum method from annual rings in the disks is higher than the CO2 content in atmospheric air. In the disks, we observe an annual trend in the CO2 concentration, correlating in a number of cases with a rise in atmospheric CO2. The annual trend in the average value of the CO2 concentration change sign from positive to negative. We hypothesize that the observed pattern for the annual distribution of CO2 in the disks is connected with a rise in atmospheric CO2 and a change in the concentration gradient between stem and atmospheric CO2.

Multi-location measurements of greenhouse gases and emission rates of methane and ammonia from a naturally-ventilated barn for dairy cows

Measurements of the gaseous emissions in livestock buildings are important as these pollutants may affect the health of farmers and the surrounding environment. Emission monitoring enables judgements on the effectiveness of mitigation strategies and controls on emission targets. The concentrations of CH 4 , N 2 O, NH 3 and CO 2 were measured in a naturally-ventilated dairy cattle building using a photoacoustic multi-gas analyser 1412 and a multiplexer 1309 (Lumasense Technologies SA, Ballerup, Denmark). The building had 164–195 Holstein dairy cows. The milk production was 31–33 kg cow −1 d −1 . Manure gutters beneath the partially slatted floor in the building were scraped twice a day. Measurements took place during the winter when the cows were permanently indoors and during 1 week in the spring when the cows were indoors at night and outside grazing during the daytime. The indoor concentrations were measured at nine evenly distributed locations, while outdoor concentrations were measured at two locations. The mean ventilation rate in winter was 250–265 m 3 LU −1 h −1 and in spring, it was 401 m 3 LU −1 h −1 . The emissions of NH 3 and CH 4 were in the range of 0.89–1.13 and 9–13 g LU −1 h −1 , respectively. A strong positive correlation was found between enhanced CO 2 and CH 4 concentrations.

Activity of Rh/TiO2 catalysts in NaBH4 hydrolysis: The effect of the interaction between RhCl3 and the anatase surface during heat treatment

The reaction properties of Rh/TiO2 sodium tetrahydroborate hydrolysis catalysts reduced directly in the reaction medium depend on the temperature at which they were calcined. Raising the calcination temperature to 300°C enhances the activity of the Rh/TiO2 catalysts. Using diffuse reflectance electronic spectroscopy, photoacoustic IR spectroscopy, and chemical and thermal analyses, it is demonstrated that, as RhCl3 is supported on TiO2 (anatase), the active-component precursor interacts strongly with the support surface. The degree of this interaction increases as the calcination temperature is raised. TEM, EXAFS, and XANES data have demonstrated that the composition and structure of the rhodium complexes that form on the titanium dioxide surface during different heat treatments later determine the state of the supported rhodium particles forming in the sodium tetrahydroborate reaction medium.

Ammonia monitoring at ppb level using photoacoustic spectroscopy for environmental application

A novel photoacoustic (PA) trace-ammonia analyzer for measuring ambient ammonia concentration in the lower ppb concentration range has been developed. It is based on a wavelength-modulated, telecommunication type, room temperature-operated diode laser light source, an acoustically optimized, longitudinal resonator type small volume photoacoustic cell and a compact multi-functional electronics unit, which ensures the fully automatic long-term operation of the system. It has a response time below 2 min, which is achieved by using a photoacoustic cell made of polyvinylidene fluoride (PVDF) and gas-handling tubes made of polyamide 11 (PA-11). A dual wavelength measurement method with optimized measurement wavelengths and laser modulation parameters was introduced, which proved to efficiently suppress cross-sensitivity to other atmospheric components, most importantly to water vapor, while improving the sensitivity of the system. The developed PA system was tested with reference to a continuous-flow denuder system (AMANDA) under both laboratory and simulated field conditions, and it featured highly reliable, fully automatic operation with a detection limit of about 50 ppb of ammonia.

A multi-dimensional transfer function approach to photo-acoustic signal analysis

Photo-acoustic signal generation has shown potential for medical tomography. This paper aims to present a consistent and unified approach to the mathematical modelling of the photo-acoustic problem, using a transfer function approach. A generalized version of the Fourier slice theorem is presented and proved. Reconstruction algorithms can be developed based on specific cases of this general theorem. Closed-form solutions to special cases are given in Cartesian, cylindrical and spherical polar coordinates. These can be used to simulate the forward problem and as test cases for any reconstruction algorithms.

Experimental and numerical investigation of airflow and contaminant transport in an airliner cabin mockup

The study of airflow and contaminant transport in airliner cabins is very important for creating a comfortable and healthy environment. This paper shows the results of such a study by conducting experimental measurements and numerical simulations of airflow and contaminant transport in a section of half occupied, twin-aisle cabin mockup. The air velocity and air temperature were measured by ultrasonic and omni-directional anemometers. A gaseous contaminant was simulated by a tracer gas, sulfur hexafluoride or SF 6, and measured by a photo-acoustic multi-gas analyzer. A particulate contaminant was simulated by 0.7 μm di-ethyl-hexyl-sebacat (DEHS) particles and measured by an optical particle sizer. The numerical simulations used the Reynolds averaged Navier–Stokes equations based on the RNG k–ε model to solve the air velocity, air temperature, and gas contaminant concentration; and employed a Lagrangian method to model the particle transport. The numerical results quantitatively agreed with the experimental data while some remarkable differences exist in airflow distributions. Both the experimental measurements and computer simulations were not free from errors. A complete and accurate validation for a complicated cabin environment is challenging and difficult.

Determination of Nitrate Concentration in Soil via Photoacoustic Spectroscopy Analysis of Ion Exchange Membranes

Numerous works have demonstrated that ion exchange membranes can be used for accurate determination of the availability of nitrate and other key nutrients in soils. After letting the ion exchange membrane interact with the soil for a known period of time, the membrane is typically immersed in a strong reagent to desorb the ions and the resulting solution is analyzed by standard chemical methods. The present study shows that mid-infrared photoacoustic spectroscopy can be used to estimate directly the amount of nitrate sorbed onto such membranes and could replace advantageously the standard chemical analysis. The study was conducted with two commercially available membranes, and in both cases the average determination error achieved with a simple partial least squares model was approximately 1.6-1.8 microeq, which under the specific experimental conditions corresponds to approximately 4.5-5.0 mg[N]/kg[dry soil]. Such errors are about 30% larger than those reported in a previous study in which the membrane was analyzed by transmittance spectroscopy. However, the present method is suitable for a much wider range of membranes, such as those commonly used for water treatment and that are too thick for transmittance measurements. For such membranes, photoacoustic spectroscopy is a very cheap and rapid alternative to standard chemical analysis.

Application of maximum length sequences to photoacoustic chemical analysis

There is a great need for inexpensive, rugged, portable, and versatile chemical detectors for use in both security and environmental measurement. Current sensors that meet the inexpensive, portable, and rugged criterion are usually limited in sensitivity and dedicated to detecting a limited number of chemicals. Sensors designed for airborne measurement typically cannot be used to measure surface chemicals. The photoacoustic method is one of the most sensitive techniques for trace analysis in both the air and on surfaces. Unfortunately, photoacoustic systems are typically expensive, usually not portable, and usually cannot be used for both airborne and surface chemical analysis. A new design for a photoacoustic measurement system is proposed that utilizes maximum length sequences (MLS) to modulate multiple, inexpensive, fixed frequency, laser diodes. The MLS modulation and post-acquisition correlation processing should provide a very high signal-to-noise measurement without need for lock-in amplifiers, high power pulsed lasers, optical modulators, or resonant measurement cells. These changes should allow for the design of a rugged, portable, inexpensive photoacoustic measurement system that can be used for both airborne and surface trace chemical detection.

Phototransformation of C60 Thin Films by UV Pulsed Laser Irradiation: Comparative Photoacoustic, AFM, and Raman Studies

Fullerene C60 films deposited by sublimation were irradiated with Kr-F laser in a wide fluence interval from 15 to 40 mJ/cm2. In situ photoacoustic analysis was applied to study the phase transformation during the irradiation. The results obtained were discussed in conjunction with atomic force microscopy (AFM) and Raman spectroscopy data. It was found that for a irradiation fluence interval from 22 to 30 mJ/cm2, 80% of C60 undergoes photopolymerization (presumably through 2 + 2 cycloaddition). For a laser energy higher than 30 mJ/cm2, a new amorphous carbon phase forms, having a large content of diamond-like, tetra-amorphous carbon (ta-C).

Validation of Ammonia Emissions from Dairy Cow Manure Estimated with a Non-Steady-State, Recirculation Flux Chamber with Whole-Building Emissions

A non-steady-state flux chamber with recirculation airflow was constructed and coupled with a portable photoacoustic multi-gas analyzer to determine ammonia emissions from dairy manure. The objective of this work was to validate this flux chamber system by performing a comparison between the flux chamber emission rates and whole-building emission rates calculated from an ammonia balance in a mechanically ventilated experimental test room. It was found that flux chamber emission estimates were greatly improved with the addition of internal air recirculation to provide air velocity over the enclosed manure surface. Validation tests of the recirculation flux chamber showed a 9% to 37% underestimation of the emissions calculated from the ammonia balance (R2 = 0.72). The non-steady-state, recirculation flux chamber method can be used to estimate ammonia emissions in naturally ventilated buildings with an accuracy comparable to other available methods. However, the validation tests showed high variability in the results, which is thought to be associated with the different consistency of the manure used in the experiments and the airflow dynamics over the enclosed manure surface.

Verifying Three Types of Methane Fluxes from Soils by Testing the Performance of a Novel Mobile Photoacoustic Method versus a Well-Established Gas Chromatographic One

The performance of a novel portable, tunable diode laser, resonant photoacoustic (TDL-PA) analyzer developed for field measurements of CH4 was compared to a commonly applied offline gas chromatographic (GC) method. This comparative studywas realized under normal field conditions parallel to long-term weekly GC monitoring of four different soil types with very different methane budgets. The method used for gas-exchange measurements was the well-known closed-chamber technique. The TDL-PA analyzer detects methane at 1650.957 nm [R (5) line of the 2v3 band], guaranteeing high precision without the need for correction procedures. The two techniques correlated well (R2 = 0.988) over the entire concentration range (0.15-33 ppmv CH4) tested at highly varying flux rates between -30 and -12 ppbv CH4 min(-1) for uptakes and between 2.5 and 362 ppbv CH4 min(-1) for emissions. The two analyzers proved to be interchangeable, leaving the online advantages to the TDL-PA. A suitable CH4 online GC solution for chamber measurement is not available as a portable system. Additionally, the data sampling rate of 2 Hz enables a direct coupling to other infrared gas analyzers with the high time resolution commonly required to determine plant CO2 assimilation rates or soil respiration rates.

Photoacoustic spectroscopic analysis of photoinduced change in absorption of titanium(IV) oxide photocatalyst powders: A novel feasible technique for measurement of defect density

Photoabsorption properties of titanium(IV) oxide powders were investigated by photoacoustic (PA) spectroscopy. The photoacoustic spectra obtained under steady-state ultraviolet irradiation showed appearance and growth of two kinds of PA signal bands, which were attributable to trivalent titanium species (Ti 3+) and trapped holes or surface peroxide species. The saturation limit of the PA signal was estimated by analyzing the time course of Ti 3+ signals and compared to the density of Ti 3+ determined by a photochemical method. The results suggest that the photoacoustic spectroscopic technique is a feasible alternative method for estimation of Ti 3+ as an empirical measure of defect density.

Comparison of Continuous and Filter-Based Carbon Measurements at the Fresno Supersite

Results from six continuous and semicontinuous black carbon (BC) and elemental carbon (EC) measurement methods are compared for ambient samples collected from December 2003 through November 2004 at the Fresno Supersite in California. Instruments included a multi-angle absorption photometer (MAAP; λ = 670 nm); a dual-wavelength (λ = 370 and 880 nm) aethalometer; seven-color (λ = 370, 470, 520, 590, 660, 880, and 950 nm) aethalometers; the Sunset Laboratory carbon aerosol analysis field instrument; a photoacoustic light absorption analyzer (λ = 1047 nm); and the R&P 5400 ambient carbon particulate monitor. All of these acquired BC or EC measurements over periods of 1 min to 1 hr. Twenty-four-hour integrated filter samples were also acquired and analyzed by the Interagency Monitoring of Protected Visual Environments (IMPROVE) thermal/optical reflectance carbon analysis protocol. Site-specific mass absorption efficiencies estimated by comparing light absorption with IMPROVE EC concentrations were 5.5 m2/g for the MAAP, 10 m2/g for the aethalometer at a wavelength of 880 nm, and 2.3 m2/g for the photoacoustic analyzer; these differed from the default efficiencies of 6.5, 16.6, and 5 m2/g, respectively. Scaling absorption by inverse wavelength did not provide equivalent light absorption coefficients among the instruments for the Fresno aerosol measurements. Ratios of light absorption at 370 nm to those at 880 nm from the aethalometer were nearly twice as high in winter as in summer. This is consistent with wintertime contributions from vehicle exhaust and from residential wood combustion, which is believed to absorb more shorter-wavelength light. To reconcile BC and EC measurements obtained by different methods, a better understanding is needed of the wavelength dependence of light-absorption and mass-absorption efficiencies and how they vary with different aerosol composition.