Odor Concentration Research Articles

Information measuring system for training assessors to determine the odour threshold using the dynamic olfactometry method

This article presents the results of training, selection and control of a group of assessors to determine the odour threshold. General recommendations of the European standard EN 13725: 2003 “Air quality － Determination of odour concentration by dynamic olfactometry” for the training, selection and supervision of a group of assessors were used in this work. A trained assessor team or panel is the odour measuring instrument. The dynamic olfactometry method was used to determine the concentration of odour in a gas sample. N-butanol was chosen as the odour sample. The experimental setup for the selection and training of a group of assessors to determine the odour threshold is a information measuring system. This information measuring system provides high accuracy and reliability of measurements. The authors chose the Scentroid SM 100 olfactometer and the Agilent 7800 A gas chromatography-mass spectrometer with a 5975C mass-selective detector as a mean of measuring in information system. The referenced value of odour threshold for n-butanol was set to 38 ppb for a panel of 8 selected n-butanol assessors. The number of steps in the dilution series was 6. The instrumental dilution range was 11 ppb to 145 ppb.

Variability of Odour Emissions from Selected Passive Area Source: Preliminary Analysis for a One-year Study at a Municipal Wastewater Treatment Plant in Poland

Passive area sources, such as primary settling tanks, located near wastewater treatment plants can significantly impact odour air quality. This paper presents the variability of odour emissions from the primary settling tank at the Municipal Wastewater Treatment Plant (MWWTP) during a one-year study of odour concentrations determined by dynamic olfactometry. The investigations indicated that the highest monthly average value of the specified odour emission rate was for July (49.89 ouE/m2/s). Preliminary statistical analysis results using a multiple regression model showed the statistical significance of the independent variables in the form of wastewater temperature and retention time concerning the specific odour emission rate values.

Estimating the relationship between liquid- and vapor-phase odorant concentrations using a photoionization detector (PID)-based approach.

Olfactory studies frequently utilize odor stimuli consisting of volatiles created from liquid dilutions of various chemicals. A problem arises if the researcher relies on these liquid dilutions to extrapolate vapor concentrations based on ideal gas behavior. For most chemicals, the relationship between liquid and vapor concentration deviates from these laws of proportionality due to interactions between the chemical and the solvent. Here, we describe a method to estimate vapor-phase concentrations of diluted odorants using a photoionization detector. To demonstrate the utility of this method, we assessed the relationship between liquid-/vapor-phase concentrations for 14 odorants (7 alcohols, 1 ester, and 6 aldehydes) in 5 different solvents (water, mineral oil, diethyl phthalate, dipropylene glycol, and propylene glycol). An analysis of 7 additional esters is also included to assess how carbon chain length and functional group, interacts with these solvents (for a total of 105 odorant/solvent pairs). Our resulting equilibrium equations successfully corrected for behavioral sensitivity differences observed in mice tested with the same odorant in different solvents and were overall similar to published measurements using a gas chromatography-based approach. In summary, this method should allow researchers to determine the vapor-phase concentration of diluted odorants and will hopefully assist in more accurate comparisons of odorant concentrations across olfactory studies.

Odour impact assessment using kinetics and optimization: case studies on removal of multiple volatile organo-sulphur compounds from sewage wastewater using porous functional materials.

Expanding industries and booming population have led to the increase in the installation of wastewater and sewer systems, even in close proximity to residential areas. Emissions from these installations particularly volatile organo-sulphur compounds (VOSCs) such as methyl mercaptan (CH3SH), ethyl mercaptan (C2H5SH), dimethyl sulphide (CH3SCH3) and carbon disulphide (CS2) are a nuisance to people even when present in small concentration. Strategies for removal involve addition of chemicals or other chemical processes which are generally expensive. Biofilters, on the other hand, consume large amount of energy and wash waters. Hence keeping commercialization in mind, it is important to develop a strategy which would be cost-effective and at the same time be effective to remove most of the odorous compounds present in these systems. In the present research work, granular activated carbons (GAC) are functionalized with alkali solution to improve the adsorption capacity. Liquid phase batch adsorption is performed with GAC and various functionalized activated carbons (FACs) with the help of raw sewage water from a local sewage water treatment plant. Concentration of odour was evaluated by two methods-olfactometry-based analysis for sensory measurement and GCMS-based analysis for analytical estimation of a specific odorous compound. The adsorption capacities of the functionalized GACs are higher primarily because of complex formation at the surface of modified GACs. Pseudo-second-order kinetic model agreed well with experimental results with the rate constant being 0.0191mg/l min and 0.0153mg/l min for methyl and ethyl mercaptan adsorption onto FAC-NH3. Boyd's film diffusion along with rate kinetic model supported that chemical adsorption forms the rate-limiting step. Response surface methodology (RSM) was used to optimize the removal of VOSCs with respect to different process parameters like adsorbent amount and time. The olfactometry removal of overall odour was also optimized taking 6 factors in the Box Behnken design. Variance of analysis results indicated that all the models displayed considerable goodness of fit with R2 values close to 1. Methyl mercaptan turned out to be the highest contributor to the overall odour as confirmed both from experimental and optimization study. The optimized olfactometry odour removal (77.4%) along with CH3SH removal (80.34%), C2H5SH removal (59.16%), CH3SCH3 removal (63.21%) and CS2 removal (71.95%) was found at optimum process conditions, with amount of adsorbent of 10.29g, adsorption time of 2.92h. This result indicates that methyl mercaptan (CH3SH) is the highest odour contributing component out of the studied VOSCs. The results show promising potential for the use of activated carbon as an adsorbent for removal of odorous compounds from STPs.

Neuron-glia interaction at the receptor level affects olfactory perception in adult Drosophila

Some types of glia play an active role in neuronal signaling by modifying their activity although little is known about their role in sensory information signaling at the receptor level. In this research, we report a functional role for the glia that surround the soma of the olfactory receptor neurons (OSNs) in adult Drosophila. Specific genetic modifications have been targeted to this cell type to obtain live individuals who are tested for olfactory preference and display changes both increasing and reducing sensitivity. A closer look at the antenna by Ca2+ imaging shows that odor activates the OSNs, which subsequently produce an opposite and smaller effect in the glia that partially counterbalances neuronal activation. Therefore, these glia may play a dual role in preventing excessive activation of the OSNs at high odorant concentrations and tuning the chemosensory window for the individual according to the network structure in the receptor organ.

Depolarization block in olfactory sensory neurons expands the dimensionality of odor encoding.

Upon strong and prolonged excitation, neurons can undergo a silent state called depolarization block that is often associated with disorders such as epileptic seizures. Here, we show that neurons in the peripheral olfactory system undergo depolarization block as part of their normal physiological function. Typically, olfactory sensory neurons enter depolarization block at odor concentrations three orders of magnitude above their detection threshold, thereby defining receptive fields over concentration bands. The silencing of high-affinity olfactory sensory neurons produces sparser peripheral odor representations at high-odor concentrations, which might facilitate perceptual discrimination. Using a conductance-based model of the olfactory transduction cascade paired with spike generation, we provide numerical and experimental evidence that depolarization block arises from the slow inactivation of sodium channels-a process that could affect a variety of sensory neurons. The existence of ethologically relevant depolarization block in olfactory sensory neurons creates an additional dimension that expands the peripheral encoding of odors.

A new method for evaluating nuisance of odorants by chemical and sensory analyses and the assessing of masked odors by olfactometry

The odor threshold concentration and the odor nuisance concentration of the nine persistent odorants at two wastewater treatment facilities were determined by Weber- Fechner curves for each odorant using dynamic olfactometry combined with the odor profile method. The odor threshold concentration results, representing each odorant's concentration at odor intensity of one (I = 1), were within range in the literature. The nuisance concentrations were determined by interpolation along the curves intersecting with the arbitrary odor intensity of three (I = 3). There is no reference that exists in the literature about determining odor nuisance concentrations for a complete set of odorants from any facility. The nuisance concentration results presented here are novel to odor control because they can provide information defining the nuisance odorant's isopleths in modeling and in designing effective odor control systems that avoid public nuisance.Dynamic olfactometry combined with the odor profile method was also used with actual foul air samples from different sources. When analyzed from raw to increased dilution, it was observed that the fecal and sulfur odors initially prominent (with no musty odors detected) gradually changed with increased dilution. Musty odors began to gradually appear while the fecal and sulfur odors became undetectable. We named this observation the “peeling of an onion effect”. It is speculated that this occurs because the musty odors in the concentrated foul air sample are masked by the fecal and the sulfur odors.

Application of different packing media for the biofiltration of gaseous effluents from waste composting

ABSTRACT A pilot-scale experiment was implemented in a waste bioreactor with an inner capacity of 1 m3 in order to simulate a real-scale composting process. The waste underwent composting conditions that are typical of the initial bio-oxidation phase, characterised by a high production of volatile organic compounds (VOCs), hydrogen sulphide (H2S) and odorants. The waste bioreactor was fed with an intermittent airflow rate of 6 Nm3/h. The target of this study was to investigate the air treatment performance of three biofilters with the same size, but filled with different filtering media: (1) wood chips, (2) a two-layer combination of lava rock (50%) and peat (50%), and (3) peat only. The analyses on air samples taken upstream and downstream of the biofilters showed that the combination of lava rock and peat presents the best performance in terms of mean removal efficiency of odour (96%), total VOCs (95%) and H2S (77%) concentrations. Wood chips showed the worst abatement performance, with respective mean removal efficiencies of 90%, 88% and 62%. From the results obtained, it is possible to conclude that the combination of lava rock and peat can be considered as a promising choice for air pollution control in waste composting facilities.

The Locust antenna as an odor discriminator

Identifying chemical odors rapidly and accurately is critical in a variety of fields. Due to the limited human sense of smell, much effort has been dedicated to the development of electronic sensing devices. Despite some recent progress, such devices are still no match for the capabilities of biological (animal) olfactory sensors, which are light, robust, versatile, and sensitive. Consequently, scientists are turning to a new approach: Bio-Hybrid sensors. These sensors combine animal biological sensors with electronic components to achieve maximum detection and classification while conveying a comprehensible signal to the end user.In this work, we created a bio-hybrid odor discriminator utilizing the desert locust's primary olfactory apparatus - its antennae, together with simple electroantennogram technology and artificial intelligence tools for signal analysis. Our discriminator is able to differentiate between at least eight pure odors and two mixtures of different odorants, independently of odorant concentration. With four orders of magnitude higher sensitivity than gas chromatography–mass spectrometry, it is able to detect the presence of less than 1 ng of volatile compounds and, compared to other bio-hybrid sensors available today, it can be easily operated by an unskilled individual. This study thus opens up the future for robust and simple bio-hybrid robotic sensing devices that can be widely deployed.

Pleasantness Recognition Induced by Different Odor Concentrations Using Olfactory Electroencephalogram Signals.

Olfactory-induced emotion plays an important role in communication, decision-making, multimedia, and disorder treatment. Using electroencephalogram (EEG) technology, this paper focuses on (1) exploring the possibility of recognizing pleasantness induced by different concentrations of odors, (2) finding the EEG rhythm wave that is most suitable for the recognition of different odor concentrations, (3) analyzing recognition accuracies with concentration changes, and (4) selecting a suitable classifier for this classification task. To explore these issues, first, emotions induced by five different concentrations of rose or rotten odors are divided into five kinds of pleasantness by averaging subjective evaluation scores. Then, the power spectral density features of EEG signals and support vector machine (SVM) are used for classification tasks. Classification results on the EEG signals collected from 13 participants show that for pleasantness recognition induced by pleasant or disgusting odor concentrations, considerable average classification accuracies of 93.5% or 92.2% are obtained, respectively. The results indicate that (1) using EEG technology, pleasantness recognition induced by different odor concentrations is possible; (2) gamma frequency band outperformed other EEG rhythm-based frequency bands in terms of classification accuracy, and as the maximum frequency of the EEG spectrum increases, the pleasantness classification accuracy gradually increases; (3) for both rose and rotten odors, the highest concentration obtains the best classification accuracy, followed by the lowest concentration.

Spike frequency adaptation facilitates the encoding of input gradient in insect olfactory projection neurons

The olfactory system in insects has evolved to process the dynamic changes in the concentration of food odors or sex pheromones to localize the nutrients or conspecific mating partners. Experimental studies have suggested that projection neurons (PNs) in insects encode not only the stimulus intensity but also its rate-of-change (input gradient). In this study, we aim to develop a simple computational model for a PN to understand the mechanism underlying the coding of the rate-of-change information. We show that the spike frequency adaptation is a potential key mechanism for reproducing the phasic response pattern of the PN in Drosophila. We also demonstrate that this adaptation mechanism enables the PN to encode the rate-of-change of the input firing rate. Finally, our model predicts that the PN exhibits the intensity-invariant response for the pulse and ramp odor stimulus. These results suggest that the developed model is useful for investigating the coding principle underlying olfactory information processing in insects.

Odor perception of aromatherapy essential oils with different chemical types: Influence of gender and two cultural characteristics.

Olfactory perception, and especially affective responses of odors, is highly flexible, but some mechanisms involved in this flexibility remain to be elucidated. This study investigated the odor perceptions of several essential oils used in aromatherapy with emotion regulation functions among college students. The influences of people's characteristics including gender, hometown region, and fragrance usage habit on odor perception were further discussed. Odor perception of nine essential oils, which can be divided into the ester-alcohol type (e.g., lavender oil) and terpene type (e.g., lemon oil) were evaluated under three odor concentrations. The results indicated that chemical type, but not concentration, significantly influenced the odor perception and there was no interaction between the two factors in this study. The arousal and emotional perception scores of odors with terpene-type oil were significantly higher than odors with ester-alcohol type. In terms of people's characteristics, participants from the southern Yangtze river gave a higher familiarity rating to almost all of these odors. The habits of fragrance usage also significantly influenced some of the odors' subjective intensity and emotional perception ratings. However, there were no significant gender differences in most of the odor perceptions. In addition, familiarity and pleasantness were positively correlated, and emotional perception and subjective intensity also showed a weak correlation. These results suggested that users' cultural characteristics could be considered to be important factors that affect the essential oil's odor perception in aromatherapy.

Rapid determination of chemical concentration and odor concentration of paint-emitted pollutants using an electronic nose

Volatile pollutants emitted from building materials are an important source of indoor air pollution. The development of rapid determination methods for the chemical concentration and odor concentration of these volatile pollutants is of great importance. The present work investigated the difference in the concentration of pollutants emitted by various paint samples, from which key pollutants (methyl isobutyl ketone, ethylbenzene, and xylene) were screened based on their concentration and odor contribution. Then, an electronic nose (E-nose) device was developed to determine the chemical concentrations of key pollutants and the odor concentration of gas emitted by paint samples. A total of 135 gas samples emitted by the selected paint were measured by the developed E-nose, by gas chromatography–mass spectrometry and by olfactory testing. The obtained sensor response values and chemical and odor concentrations were divided randomly and used for training and testing of the E-nose pattern recognition algorithm. The trained pattern recognition algorithm was able to accurately output the target values, with average relative errors of 10.0%, 10.4%, 7.6%, and 10.0% (test set, n = 13) for the methyl isobutyl ketone, ethylbenzene, and xylene chemical concentrations and the odor concentration, respectively. In addition, the cross-sensitive nature of the E-nose showed a unique advantage in determining odor concentration compared to the odor conversion model. The excellent performance of the developed E-nose demonstrates that this work provides a practical solution for the rapid determination of the chemical concentration and odor concentration of pollutants emitted by building materials.

Changes in odorants and flavor profile of heat-processed beef flavor during storage.

Flavor quality changes of heat-processed beef flavor (HPBF) upon storage are greatly affected by storage conditions. Flavor characterization of HPBF stored for 168 days resulted in 17 key odor-active compounds having flavor dilution factors log3 FD ≥ 3 and odor activity values >1. Based on the concentration changes of these key odorants, a total of 13 HPBF samples were divided into four groups by hierarchical cluster analysis. Combined with flavor profile analysis, the overall flavor of HPBF gradually changed from a characteristic beef aroma to burnt and fermented soybean paste-like notes. Some of the 17 key odorants, such as 2-methyl-3-furanthiol, 2-furfurylthiol, methyl furfuryl disulfide, and difurfuryl disulfide, contributed to the characteristic beef aroma of the freshly prepared product and in the early stage of storage. On the other hand, the odor-active compounds 2-methylbutanal, dimethyl disulfide, dimethyl trisulfide, and 2-ethyl-3,5-dimethylpyrazine were associated with the later stage of storage showing a positive correlation with the intensity of burnt and fermented soybean paste-like notes. A molecular understanding of flavor profile changes of HPBF during storage will provide the basis for developing characteristic beef aroma notes and maintaining the keeping quality of beef products upon storage. PRACTICAL APPLICATION: The relationship between sensory quality and changes in odorant concentration of heat-processed beef flavor during storage will provide the molecular basis for developing high-quality thermal reaction meat flavorings.

A study on the relationship between odor hedonic ratings and individual odor detection threshold

Odor hedonic perception (pleasant/unpleasant character) is considered as the first and one of the most prominent dimensions in olfaction and is known to depend on several parameters. Among them, the relation between the odorant concentration and the hedonic estimation has been widely studied. However, few studies have considered odor hedonic ratings (OHR) in relation to individual detection thresholds (IDT). Thus, the aim of this study was to determine olfactory detection thresholds and to describe hedonic rating variations from individual thresholds to higher concentrations. IDT were performed for two pleasant (apple and jasmine) and two unpleasant (durian and trimethylamine) odorant stimuli. The experimenter presented one by one in a randomized order, the different odorant concentrations above IDT. Participants rated odor hedonic valence of these stimuli on a visual analog scale. Results showed, except for trimethylamine, the same relationship between hedonic ratings and stimulus concentration, i.e., an increase of pleasantness (apple and jasmine)/unpleasantness (durian) ratings at low and middle concentrations followed by a plateau at high concentrations. Correlations between OHR and concentrations as well as between OHR and threshold steps were always significant. Moreover, comparisons between both conditions showed that the correlation coefficient was significantly higher for trimethylamine (and a trend for apple) when IDTs were considered, while no difference was found for jasmine and durian. Overall, results suggested that the relationship between OHR and IDT is odor specific. These findings contribute to explain the large variability of the hedonic tone (i.e., weakly vs. very pleasant, weakly vs. very unpleasant) at specific concentration in the general population and could serve future research in this field (e.g., olfactory preferences in nutrition studies, anhedonia in psychiatric disorders…).

Comparison of Different Natural Gas Flow Rates in Pipelines and their Effect on Odorant Concentration

Comparison of Different Natural Gas Flow Rates in Pipelines and their Effect on Odorant Concentration

A new air cleaning technology to synergistically reduce odor and bioaerosol emissions from livestock houses

Odor and bioaerosols have serious impacts on the biological safety of animal production and the ecological environment. Thus, it is particularly important to explore synergistic air cleaning technology to solve these problems. In this study, a pilot-scale air cleaning equipment were applied to an experimental manure storage house to determine the removal efficiency of gaseous pollution using four treatments groups. These treatment groups include acid scrubbing + caustic scrubbing (AC), acid scrubbing + caustic scrubbing + photocatalytic oxidation (ACP), acid scrubbing + caustic scrubbing + biological scrubbing (ACB), and acid scrubbing + caustic scrubbing + biological scrubbing + photocatalytic oxidation (ACBP). Results showed that ACP can synergistically remove odor and bioaerosol, with ammonia, odor concentrations, hydrogen sulfide, methyl mercaptan, methyl sulfide, bacterial aerosol, and fugal aerosol removal efficiencies of 89.1 %, 76.3 %, 100 %, 94.2 %, 91.2 %, 75.6 %, and 83.6 %, respectively. Furthermore, ACBP has the highest removal efficiency of 79.2 % for odor concentration, but this combination has a low inactivation efficiency (< 25 %) for bacterial aerosols. Moreover, adding biological scrubbing before photocatalytic can reduce the conversion from aromatic hydrocarbons to Oxygenated VOCs. Findings of this study provide a theoretical basis and technical support for the application of air cleaning technology in livestock houses.

Advanced Oxidation Processes to Reduce Odor Emissions from Municipal Wastewater—Comprehensive Studies and Technological Concepts

Municipal facilities can generate odors caused by substances such as fatty acids, organosulfur compounds, aldehydes, and inorganic gases, especially H2S. Identifying an effective and cost-efficient solution to the problem is a priority for communities in areas at risk of exposure to odors. The aim of this study was to evaluate the effect of advanced oxidation processes (AOPs) involving Fenton’s reagents (Fe2+/H2O2, Fe3+/H2O2) on wastewater profiles and their capacity to reduce putrescibility, H2S emissions, and odor concentration in the air. The Fe2+/H2O2 system proved to be the most efficient in terms of inhibiting the process of redox conditions development, removing organic matter in the wastewater, inhibiting H2S formation, and reducing odor emissions. H2S generation in raw wastewater was triggered as early as on day 2 of anaerobic retention, with levels of 5.6 ppm to 64 ppm. After introduction of 0.1 g Fe2+/dm3 and 2.0 g H2O2/dm3, no H2S was detected in the gas for 8 days. The odor concentration (OC) of raw wastewater (2980 ± 110 oue/m3) was reduced by 96.3 ± 1.9% to a level of 100 ± 15 oue/m3. The Fe2+/H2O2 system maintained its oxidizing capacity up until day 7, with OC reduction by 96.0 ± 0.8% to a level of 120 ± 10 oue/m3. On day 10, the OC showed a marked increase to a level 1310 ± 140 oue/m3. The conducted research has proven that Fenton-based AOP systems are a technologically and commercially viable method of deodorization of sewage facilities.

Application of non-thermal plasma (NTP) for volatile compounds (VCs) removal at sewage sludge composting facility

Double dielectric barrier discharge (DDBD) reactors were used to evaluate the removal efficiency of volatile compounds (VCs) from the exhaust gas of sewage sludge (SS) composting facility at optimal conditions, i.e., input power 65.8W, gas feeding rate 4 L/min, plasma discharge gap 6 mm. Abatement of VCs from different processing periods of SS composting was determined. 100% removal of major species of VCs (methyl isobutyl ketone, carbon disulfide, chlorobenzene and methylene chloride, etc.) were determined during the ‘before turning (B.T)’ and ‘5 h after turning (A.T)’ process. In addition, the synergistic effect of plasma-catalyst (Pt–Sn/Al2O3, BaTiO3 and HZSM-5) on VCs abatement showed enhanced removal performance as the formation of reactive species (H and OH radicals) was increased, especially on the surface of the catalyst. Nevertheless, plasma alone and plasma-catalyst combine systems showed the most effective reduction in odor concentration at the ‘B.T’ process due to low initial concentration. The study could facilitate NTP-DDBD technology application and process optimization in exhaust gases treatment of composting plants.

Immature olfactory sensory neurons provide behaviourally relevant sensory input to the olfactory bulb

Postnatal neurogenesis provides an opportunity to understand how newborn neurons integrate into circuits to restore function. Newborn olfactory sensory neurons (OSNs) wire into highly organized olfactory bulb (OB) circuits throughout life, enabling lifelong plasticity and regeneration. Immature OSNs form functional synapses capable of evoking firing in OB projection neurons but what contribution, if any, they make to odor processing is unknown. Here, we show that immature OSNs provide odor input to the mouse OB, where they form monosynaptic connections with excitatory neurons. Importantly, immature OSNs respond as selectively to odorants as mature OSNs and exhibit graded responses across a wider range of odorant concentrations than mature OSNs, suggesting that immature and mature OSNs provide distinct odor input streams. Furthermore, mice can successfully perform odor detection and discrimination tasks using sensory input from immature OSNs alone. Together, our findings suggest that immature OSNs play a previously unappreciated role in olfactory-guided behavior.