Methodological Comparison between a Novel Automatic Sampling System for Gas Chromatography versus Photoacoustic Spectroscopy for Measuring Greenhouse Gas Emissions under Field Conditions

Photoacoustic Spectroscopy Gas Detection Technology Research Progress

Photoacoustic spectroscopy (PAS) can be utilized as an ultrasensitive gas detection method. The basic principles of gas detection using PAS are discussed in this paper. First, the basic instrumentation for a PAS gas detection system is introduced focusing on the photoacoustic cell. The discussion includes non-resonant photoacoustic cells and the different types of resonant photoacoustic cells, including the longitudinal photoacoustic cell, the Helmholtz photoacoustic cell, the T-type photoacoustic cell, and the high-frequency resonant photoacoustic cell. The basic working principles of each of these, cells as well as the advantages and disadvantages of photoacoustic cells are discussed, and the development of newer types of photoacoustic cells in recent years is outlined in detail. This review provides detailed reference information and guidance for interested researchers who would like to design and build advanced photoacoustic cells for gas detection.

Acidification of slurry to reduce ammonia and methane emissions: Deployment of a retrofittable system in fattening pig barns

Livestock farming, and in particular slurry management, is a major contributor to ammonia (NH₃) and methane (CH₄) emissions in Europe. Furthermore, reduced NH₃ and CH₄ emissions are also relevant in licensing procedures and the management of livestock buildings. Therefore, the aim is to keep emissions from the barn as low as possible. Acidification of slurry in the barn can reduce these environmental and climate-relevant emissions by a pH value of 5.5. In this study, an acidification technology was retrofitted in an existing fattening pig barn equipped with a partially slatted floor. The slurry in a compartment with 32 animals was acidified. An identical compartment was used for reference investigations (case-control approach). Several times a week slurry was pumped for acidification in a process tank outside the barn compartment in a central corridor, where sulphuric acid (H₂SO₄) was added. Then the slurry was pumped back into the barn. In contrast to other systems, where acidified slurry was stored mainly in external storage tanks, in this study the slurry was completely stored in the slurry channels under the slatted floor, during the entire fattening period. The emission mass flow of NH₃ and CH₄ was measured continuously over three fattening periods, with one period in spring and two periods in summer. On average 17.1 kg H₂SO₄ (96%) (m³ slurry)^-1 were used for acidification during the three fattening periods. NH₃ and CH₄ emissions were reduced by 39 and 67%, respectively. The hydrogen sulphide (H₂S) concentration in the barn air of the acidification compartment was harmlessly low (0.02 ppm). Thus, despite the storage of the acidified slurry in the barn, the system leads to a lower concentration of detrimental gases, which is beneficial for the animals' as well as for the workers' health. The study shows that it is possible to retrofit acidification technology into existing pig barns. Further investigations shall identify possible measures to reduce the amount of H₂SO₄ used and thus minimise the sulphur input into the slurry.

Photoacoustic Detection of Pollutants Emitted by Transportation System for Use in Automotive Industry

In photoacoustic spectroscopy, the signal is inversely proportional to the resonant cell volume. Photoacoustic spectroscopy (PAS) is an absorption spectroscopy technique that is suitable for detecting gases at low concentrations. This desirable feature has created a growing interest in miniaturizing PA cells in recent years. In this paper, a simulation of a miniaturized H-type photoacoustic cell consisting of two buffer holes and a resonator was performed in order to detect CO, NH3, NO, and CH4 pollutants. These gases are the main components of the air pollutants that are produced by the automotive industry. The linear forms of the continuity, Navier–Stokes equations, and the energy equation were solved using the finite element method in a gaseous medium. The generated pressure could be measured by a MEMS sensor. Photoacoustic spectroscopy has proven to be a sensitive method for detecting pollutant gases. The objectives of the measurements were: determining the proper position of the pressure gauge sensor; measuring the frequency response; measuring the frequency response changes at different temperatures; studying the local velocity at the resonant frequency; and calculating the quality factor. The acoustic quality coefficient, acoustic response (pressure), local velocity, frequency response, and the effect of different temperatures on the frequency response were investigated. A frequency response measurement represents the fact that different gases have different resonance frequencies, for which CO and NO gases had values of 23.131 kHz and 23.329 kHz, respectively. The difference between these gases was 200 Hz. NH3 and CH4 gases with values of 21.206 kHz and 21.106 kHz were separable with a difference of 100 Hz. In addition, CO and NO gases had a difference of 2000 Hz compared to NH3 and CH4, which indicates the characteristic fingerprint of the designed cell in the detection of different gases. Better access to high-frequency acoustic signals was the goal of the presented model in this paper.

Effect of Wearing Surgical Face Masks on Gas Detection from Respiration Using Photoacoustic Spectroscopy

Wearing surgical face masks is among the measures taken to mitigate coronavirus disease (COVID-19) transmission and deaths. Lately, concern was expressed about the possibility that gases from respiration could build up in the mask over time, causing medical issues related to the respiratory system. In this research study, the carbon dioxide concentration and ethylene in the breathing zone were measured before and immediately after wearing surgical face masks using the photoacoustic spectroscopy method. From the determinations of this study, the C₂H₄ was established to be increased by 1.5% after one hour of wearing the surgical face mask, while CO₂ was established to be at a higher concentration of 1.2% after one hour of wearing the surgical face mask, when the values were correlated with the baseline (control).

Greenhouse gas formation during the ensiling process of grass and lucerne silage

Silage is an essential global feedstuff and an emitter of greenhouse gases. However, few studies have examined the formation of carbon dioxide (CO₂), nitrous oxide (N₂O) and methane (CH₄) during the ensiling process. This study aimed to record the course of gas concentrations in forage during the ensiling process and determine the temporal variation in the (microbiological) formation processes. Grass and lucerne, each with two different dry matter (DM) concentrations (four variants, each n = 3), were ensiled in laboratory-scale barrels (120 L). Gas samples were taken from the headspace of the barrels and analysed using a gas chromatograph. The measurement period included the first 49 days of the ensiling process and the measurement interval was 0.5-48.0 h. For all variants, a rapid increase in CO₂ concentration and a one-time N₂O concentration peak was observed between ensiling hours 36 and 96. Lower DM concentration led to significantly faster CO₂ production (p < 0.05). Lucerne forage and higher DM concentrations led to significantly increased N₂O concentrations (p < 0.05). The extensive measurements demonstrated that butyric acid formation by clostridia contributes to CH₄ formation; thus, lucerne silage had a significantly higher concentration from ensiling day 13 (p < 0.05). Therefore, malfermentation actively contributes to the formation of greenhouse gases. The method described here provides further insights into greenhouse gas formation during the ensiling process and can thus help to improve ensiling research and management.

Nanostructured metal oxide semiconductor-based sensors for greenhouse gas detection: progress and challenges

Climate change and global warming have been two massive concerns for the scientific community during the last few decades. Anthropogenic emissions of greenhouse gases (GHGs) have greatly amplified the level of greenhouse gases in the Earth's atmosphere which results in the gradual heating of the atmosphere. The precise measurement and reliable quantification of GHGs emission in the environment are of the utmost priority for the study of climate change. The detection of GHGs such as carbon dioxide, methane, nitrous oxide and ozone is the first and foremost step in finding the solution to manage and reduce the concentration of these gases in the Earth's atmosphere. The nanostructured metal oxide semiconductor (NMOS) based technologies for sensing GHGs emission have been found most reliable and accurate. Owing to their fascinating structural and morphological properties metal oxide semiconductors become an important class of materials for GHGs emission sensing technology. In this review article, the current concentration of GHGs in the Earth's environment, dominant sources of anthropogenic emissions of these gases and consequently their possible impacts on human life have been described briefly. Further, the different available technologies for GHG sensors along with their principle of operation have been largely discussed. The advantages and disadvantages of each sensor technology have also been highlighted. In particular, this article presents a comprehensive study on the development of various NMOS-based GHGs sensors and their performance analysis in order to establish a strong detection technology for the anthropogenic GHGs. In the last, the scope for improved sensitivity, selectivity and response time for these sensors, their future trends and outlook for researchers are suggested in the conclusion of this article.

Effects of a Partially Perforated Flooring System on Ammonia Emissions in Broiler Housing-Conflict of Objectives between Animal Welfare and Environment?

Simple Summary

Previous studies have shown positive effects of a partially perforated flooring system on animal welfare in broiler housing. Towards the end of the fattening periods, the present study showed a higher ammonia emission rate (NH₃ ER) for a partially perforated flooring system compared with a littered control barn. Nevertheless, the measured NH₃ concentrations were below 20 ppm, except during a mechanical litter treatment in the winter fattening period. Furthermore, the system offers the possibility of applying practical solutions that were not feasible before. By using underfloor air extraction, manure belts, or acidification systems underneath the elevated perforated area, NH₃ concentrations and the resulting NH₃ ER could be reduced. Thus, with some optimization, the partially perforated flooring system could be used to contribute to an increase in animal welfare and environmental protection at the same time.

Abstract

A partially (50%) perforated flooring system showed positive effects on health- and behavior-based welfare indicators without affecting production performance. Ammonia (NH₃) is the most common air pollutant in poultry production, with effects on animal welfare and the environment. The objectives of animal welfare and environmental protection are often incompatible. Therefore, this study addresses the question of how a partially perforated flooring system affects NH₃ emissions. According to German regulations, three fattening periods were carried out with 500 Ross 308 broilers per barn (final stocking density: 39 kg m⁻²). The experimental barn was equipped with an elevated perforated area in the supply section, accessible by perforated ramps. The remaining area in the experimental barn and the control barn were equipped with wood shavings (600 g m⁻²). Besides the different floor types, management was identical. Air temperature (Temp), relative air humidity (RH), NH₃ concentration, and ventilation rate (VR) were measured continuously. Furthermore, dry matter (DM) content, pH, and litter quality were assessed. Towards the end of the fattening periods, the NH₃ emission rate (ER) of the partially perforated flooring system was higher compared with that of the littered control barn (all p < 0.001). This effect is mainly caused by the higher NH₃ concentrations, which are promoted by the lack of compaction underneath the elevated perforated area and the increase in pH value under aerobic conditions. Nevertheless, the partially perforated flooring system offers different approaches for NH₃ reduction that were previously not feasible, potentially contributing equally to animal welfare and environmental protection.

A new experimental setup for measuring greenhouse gas and volatile organic compound emissions of silage during the aerobic storage period in a special silage respiration chamber

The aim of this study was to develop a new experimental setup to determine parallel the emissions of greenhouse gases (GHG) and volatile organic compounds (VOCs) from silage during the opening as well as the subsequent aerobic storage phase of the complete bale without wrapping film. For this purpose, a special silage respiration chamber was used in which a silage bale could be examined. The gas analysis (CO₂, methanol, ethanol, ethyl acetate) of inlet, ambient and outlet air of the silage respiration chamber was carried out by photoacoustic spectroscopy. The gas samples taken inside the bale were analysed by gas chromatography for CO₂, O₂, CH₄, and N₂O. Three silage bales (grass and lucerne) as the smallest silage unit commonly used in practice were examined. The emission behaviour of the bales was recorded during experimental periods up to 55 days. The results allow a differentiation of the outgassing processes. On the one hand, gases produced during the anaerobic ensiling process (CO₂, CH₄, N₂O) are released once in a large amount during the first experimental hours after opening the silage. On the other hand, a continuous outgassing process takes place, which is particularly true for the VOCs ethanol, methanol, and ethyl acetate, whereby VOC emissions increase with rising ambient air temperatures. In this study, the emissions during the first 600 experimental hours from the grass silage bale and lucerne silage bale were 2313 g and 2612 g CO₂, 17.6 g and 145.2 g methanol, 132.3 g and 675.9 g ethanol, 55.1 g and 66.2 g ethyl acetate, respectively. Nevertheless, the focus of this study was on the technical recording of gas concentrations inside the silage bale itself and the emissions in the ambient air of the bale. For a better interpretation of the data, additional factors should be considered in further investigations.

Validation of a New Resource-Efficient Feeding System for Fattening Pigs Using Increased Crude Fiber Concentrations in Diets: Feed Intake and Ammonia Emissions

Simple Summary

The feeding of fattening pigs and its associated ammonia emissions are current core problems in social debate that affects climate change and sustainability. Feeding methods offer great potential to increase animal welfare and sustainability, and negative impacts on the environment can be reduced. Fattening pigs differ in their performance potential and in their nutrient requirements. A high feed intake capacity can lead to luxury consumption. Diets rich in crude fiber should prevent excess feed intake and cause better nitrogen fixation by microorganisms in the animals’ large intestines. In a pig fattening farm, it was investigated whether and how diets rich in crude fiber can influence feed intake and ammonia emissions. The animals were divided into feeding groups according to their presumed performance potential by ultrasound examinations. Therein, body compositions were evaluated, and feed intake capacity and body weight were automatically recorded. The aim of the study was to enable adapted feeding of the animals by regarding their individual differences in body composition and performance potential. Roughage-based diets had significant influence on feed intake and did not increase ammonia emissions. Based on the results of this study a performance-based control of the feed intake should be made possible.

Abstract

The housing of fattening pigs, their feeding, and the emissions associated with this process are subjects of criticism. In order to reduce emissions and ensure resource efficiency, new paths must be taken; animals must be fed closer to their actual needs. In a pig fattening farm, 655 animals were grouped according their body weight and their body composition, consisting of weight and muscle-fat-ratio, which was determined by ultrasound examinations. The influence of different concentrations of triticale whole plant silage (WPS) (from 2.5% to 10%) on the feed intake capacity (3.88 kg to 2.71 kg (88% dry matter (DM))) of each group and the ability to control it was determined. Ammonia emissions were measured and the pens floor pollution was assessed. The animals could be distinguished significantly from each other by ultrasound examinations. The crude fiber influenced the level of daily feed intake. Ammonia emissions were not negatively influenced and could be partly reduced. There was no negative impact on surface contamination due to the increased use of crude fiber. The amount of daily feed intake was controlled by crude fiber rich diets. If these findings are adapted to certain types of pigs, a reduction of emissions and an increased resource efficiency can be expected.

Suitability of Different Filling Materials for a Biofilter at a Broiler Fattening Facility in Terms of Ammonia and Odour Reduction

A two-stage exhaust air treatment system installed at a broiler fattening facility with 40,000 animals was investigated. The facility’s exhaust air was treated first by use of a chemo-scrubber (stage 1) and afterwards by a vertical biofilter (stage 2). The biofilter was equipped with root wood and honeycombed paper pad layers (half/half) to enable a direct comparison of both filter materials’ suitability. Odour samples were taken on site and afterwards analysed at an olfactometry laboratory. Ammonia concentration values were collected continuously using a photoacoustic multi-gas monitor. High mitigation performance was achieved with both filter materials, with the honeycombed paper pad layer being less susceptible to fungal growth than the root wood filter. Cellulose seems to be a proper alternative for use in biofilters, but further research is needed to estimate the long-term stability of this material.

Cattle Diets Strongly Affect Nitrous Oxide in the Rumen

This study aimed at assigning climate-relevant gaseous emissions from ruminants to animal- or feed-related origin. Three adult rumen-cannulated German Holstein steers and three forage types (corn silage (CS), alfalfa silage (AS) and grass hay (GH)) were used in a 3 × 3 Latin square design. Each period consisted of 12 days (d), during which animals received 10 kg dry matter/day of one forage as sole feed. Gaseous samples from forages and the steers´ rumen were taken and analyzed for CO2, CH4, and N2O using gas chromatography. There were large differences in the amounts of CO2 and N2O emitting from the forage types. Most N2O came from AS and only small amounts from GH and CS. Results indicate that fermented forages rich in nitrogen can release climate-relevant N2O. The highest CO2 amounts were measured in CS. Methane was not detected in any forage sample. Animals consuming CS showed slightly lower CH4 concentrations in the rumen gas sample than animals fed AS or GH. Big differences were found for ruminal N2O with the highest concentration after AS ingestion such that the N2O measured in the rumen seems to originate from the used feedstuff.

Quantification of Methane and Ammonia Emissions in a Naturally Ventilated Barn by Using Defined Criteria to Calculate Emission Rates

Simple Summary

Defined criteria for the application of the CO₂ balance method in a naturally ventilated barn provided reliable data. This specification enabled the acquisition and quantification of CH₄ and NH₃ in a naturally ventilated dairy barn, as well as detecting decreasing NH₃ emissions affected by supplementing an Acacia mearnsii condensed tannin extract to a dairy cattle ration. Moreover, long-term measurements were possible and can be used to examine feed-related mitigation strategies at a barn level in the future.

Abstract

Extensive experimentation on individual animals in respiration chambers has already been carried out to evaluate the potential of dietary changes and opportunities to mitigate CH₄ emissions from ruminants. Although it is difficult to determine the air exchange rate of open barn spaces, measurements at the herd level should provide similarly reliable and robust results. The primary objective of this study was (1) to define a validity range (data classification criteria (DCC)) for the variables of wind velocity and wind direction during long-term measurements at barn level; and (2) to apply this validity range to a feeding trial in a naturally cross-flow ventilated dairy barn. The application of the DCC permitted quantification of CH₄ and NH₃ emissions during a feeding trial consisting of four periods. Differences between the control group (no supplement) and the experimental group fed a ration supplemented with condensed Acacia mearnsii tannins (CT) became apparent. Notably, CT concentrations of 1% and 3% of ration dry matter did not reduce CH₄ emissions. In contrast, NH₃ emissions decreased 34.5% when 3% CT was supplemented. The data confirm that quantification of trace gases in a naturally ventilated barn at the herd level is possible.