Odour

An scent is a mixture of volatile chemic compounds that humans and other animals perceive with the sense of olfaction and Dynamic Olfactometry is a technique that allows to assign to an scent its concentration, which is divers as the number of dilutions with odourless air required for an odour to be detected by 50% of a panel of human evaluators (CEN, 2003).

From: Atmospheric Environs , 2018

Air: Bars Animal Facilities and Air Quality Issues

S.J. Werth , ... F.M. Mitloehner , in Encyclopedia of Agronomics and Nutrient Systems, 2014

Odors

Odors from CAFOs are a major nuisance and have the potential to negatively impact the quality of life for the nearby residents (Fournel et al., 2012). Gaseous compounds associated with odor vary greatly in molecular weight and odorant strength making it challenging to quantify and compare odors. As a outcome, the concept of an 'odor unit' (OU) was developed as a way to normalize the specific odor-related consequence of an odor or mixture of odors. In that location are half dozen major groups of odorous compounds, every bit identified past Mackie et al. (1998), which includes the previously discussed air pollutants, NH3 and VOCs, and several sulfur-containing compounds.

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Landfill Functioning

Nicole D. Berge , ... Wenjing Lu , in Solid Waste Landfilling, 2018

Odor control

Odors exist due to putrescible wastes, tending sludge, landfill gases, and leachate seeps but too when organic rich waste matter is—especially in hot climate—unloaded by the collection truck. Good overall landfill operation, high compaction, the placement of daily cover, and even the firsthand covering of materials that have an offensive olfactory property, aid in decision-making odor (Farquhar et al., 1995). Employing an effective gas control organisation volition also help in mitigating aroma. Collected gas can be deodorized via thermal oxidation, wet gas scrubbing, activated carbon filtration, and biofiltration (Frechen, 1989; Feinbaum, 2000). In some cases more frequent waste collection may also help to reduce odors in the incoming waste. In extreme cases chemicals can be employed to benumb odor including ozone and mixtures containing plant oils and surfactants (O'Maley, 2003). Odour-neutralizing chemicals are often dispensed in a perimeter misting system. These measures are taken only in a few cases. Bad odors at landfills in countries located in moderate climate zones are in most cases a result of nonoptimal operation.

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Nuisance Characteristics of Chancy Air Pollutants

Jeffrey W. Bradstreet , in Hazardous Air Pollutants, 1995

x.3.ane Scent Measurement Techniques

Smell is a awareness, i.e., a conscious reaction to a chemical stimulus of our olfactory system. At that place are four sensory backdrop of aroma response. These are aroma detectability, intensity, character and hedonic tone (pleasantness and unpleasantness). The sensory property almost commonly measured is detectability, i.e., dilution of the odorous air with smell-gratuitous air until either the detection or recognition thresholds are reached. The detection threshold is that betoken where an individual or panel (6-8 people) tin can discriminate the odorous sample from odor-complimentary air and keep to practise so as concentrations are increased, fifty percentage (50%) of the fourth dimension. The recognition threshold is that point where a panelist familiar with the odor character could recognize the smell fifty percent (50%) of the fourth dimension. The recognition threshold odorant concentration generally exceeds the detection threshold by a factor of 1.5 to 10.

There are many techniques used to measure detectability or dilution-to- threshold ratio. All of them involve diluting the odorous sample with odor-free air in known ratios. The diluted samples are presented to the odour judges or panelists in an ascending order, i.east., well-nigh dilute get-go, to forbid olfactory fatigue or memory effects.

Perceived odor intensity is usually established by comparison to the standard reference odorant, 1-butanol. Standard dilutions of butanol concentrations are prepared and presented to the panelists. Other odors can then be compared to butanol to determine an intensity number.

Odor emissions are traditionally established by measuring the detectability 4 of flue gas under known, ideally worst-case, conditions. The product of scent detectability, expressed as odour dilution ratio (ED50), times volume period of the flue gas equals the odor emission rate. This term is an emission value that tin exist used in a manner similar to ambient air quality modeling to determine customs impact.

Measurement of the scent emission rate is a recommended task in determining the amount of control required. Knowledge of emission rates allows for an informed judgement of which sources are contributing to ambient impacts.

The characteristics of plume dispersion may vary from source to source depending upon tiptop of release, go out velocity, atmospheric weather, get out temperature and other release point configurations. Applying control based upon a relative ranking of scent emission alone, therefore, can lead to ineffective scent control, i.e., overcontrolling some sources and undercontrolling others. A cost-effective decision of odor command should therefore include a modeling assay of the expected impact of the scent sources under various meteorology weather condition.

Modeling of odorous bear on requires consideration of shorter term exposure than that predicted with traditional ambient air quality modeling. Predicted impacts should exist more consistent with human response to odors, i.e., minutes. Murray and Duffee 5 take developed an appropriate modeling technique for aroma impact analysis. This modeling program calculates short-term (1-2 minutes) odorous impacts for categories of meteorology conditions. Such a modeling technique affords the opportunity to realistically predict odor impacts from divers sources for expected operating conditions and possible atmospheric weather condition. This predictive analysis allows a determination of odor impact from contributing sources and thereby the extent of control needed.

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Urban and Household Pollution

J.F. Artiola , ... M.L. Brusseau , in Ecology and Pollution Science (Third Edition), 2019

18.5.3 Sources of Smell

Odors associated with raw sewage or municipal wastewater treatment are easily recognized by these two characteristics: the odor of rotten eggs and the odor rotten cabbage. At that place are numerous chemicals associated with these odors, including sulfur-based compounds like hydrogen sulfide and mercaptans, nitrogenous compounds like amines and scatole, aldehydes similar butyraldehyde, and acids like butyric acrid (Stuetz and Frechen, 2001). Individually and collectively, these chemicals produce olfactory property responses with very low thresholds and are usually associated with neighborhood nuisance complaints.

There is increasing evidence that repeated exposure to these odors produces long-lasting adverse effects including psychological furnishings, nausea, and stress (Liu et al., 1997). Although chemicals like hydrogen sulfide are very toxic, most odors act as warning signs that often become a nuisance at levels well below what are considered toxic by industrial and ambience air quality standards. For example, in the case of hydrogen sulfide, the human threshold of detection is ~   0.15–0.5   ppb–five, but OSHA has set up an occupational air safety exposure of 10   ppm–v. To avert nuisance complaints, the World Health Arrangement (WHO) recommends that ambient air hydrogen sulfide concentrations practise not exceed 0.v   ppb–v.

Ammonia gas is a large component of odors derived from animal wastes and biosolids. Ammonia gas has a very sharp, pungent smell, which is generally just clearly recognized by humans at concentrations higher up 50   ppm–v (Merck Alphabetize, 1996). Common sources of this odor include dairy corrals and beast waste product lagoons. Ammonia and other odorous gases emissions are besides of concern in the land treatment of biosolids. Fig. 18.4 shows the fluxes of ammonia from biosolids over a 3-day menstruum under laboratory weather condition.

Fig. 18.4

Fig. eighteen.4. Ammonia fluxes were measured using a chamber placed over samples of pure biosolids (~   8% biosolids), biosolids applied to the surface of dry soil, and biosolids incorporated inside dry soil. The effigy illustrates the effectiveness of reducing ammonia emissions by incorporation of the biosolids into the soil. Ammonium Northward applied within the biosolids was ~   364   kg   NHiv-Due north   ha–one.

 (From Matthias, A.D., Artiola, J.F., unpublished data.)

At that place are numerous types of odorous chemicals associated with industrial and transportation activities. A readily recognized odor is that of methyl methacrylate, which is used in the manufacture of plastics and resins. This synthetic toxic chemical is an irritant that like ammonia affects the mucous membranes and that, similar hydrogen sulfide, has a very low olfactory property threshold of ~   0.1–100   ppb–five. Odors associated with transportation include distinctive gasoline fumes that are equanimous primarily of chemicals such as benzene, xylenes, and toluene that have relatively high odor thresholds (~   0.05–iv   ppm–v) and that are known to be carcinogenic and combustible.

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Taste and aroma problems in drinkable h2o

Esther Ortenberg , Benjamin Telsch , in Handbook of Water and Wastewater Microbiology, 2003

2.1 Threshold aroma test (TOT) (Standard Methods, 1998)

The threshold odour examination is used for odour label in natural and drinkable water. The principle of the test is the determination of the least concentration of the component possessing odour in the h2o studied past diluting the h2o sample with odourless water.

The method is very elementary to perform but it is not sufficiently authentic enough when determining concentration. There is no accented threshold smell concentration because of inherent variations in individual olfactory capability. From 5 to 10 experts take part when conducting the threshold odour examination. Experiments on odour determination are carried out in a room free from odor and well ventilated by air filtered through activated carbon. Before determining the threshold smell, samples under written report are dechlorinated by means of thiosulphate and heated up to 60°C. Chemical glassware should be scent-gratis.

Interpretation of the unmarried tester result requires noesis of the relative activity of that person. Some investigators have used specific odorants (odour reference standard) to calibrate a tester's response (Krasner, 1995).

Measurements of the threshold odour are carried out past using a conventional unit, TON (threshold olfactory property number). The threshold odour number is the greatest dilution of a sample with odour-free h2o yielding a definitely perceptible odour. The TON is computed in the following mode:

T O Northward = A + B A

where A is the book sample (ml) and B is the volume of scent-free water (ml).

Conclusion is carried out in the following style: first the approximate TON level is adamant past using three to iv dilutions, then the TON value is improved by repeating the procedure but with smaller volumes of the sample under study. At this stage ii blanks (odour-gratuitous water) and ii to three odour reference standards are used. Having determined the least concentration still giving the odour, this concentration is improved by studying samples with lower or college concentrations of the odour-bearing component in water.

A threshold number is not a precise value. In the case of a single observer it represents a judgement at the time of testing. Panel results are more than meaningful considering individual differences have less influence on the outcome. One or two observers can develop useful data if comparison with larger panels has been fabricated to check their sensitivity. Comparisons of information from time to time or identify to place are not advisable unless all test atmospheric condition take been standardized carefully and at that place is some basis for the comparison of observed intensities. The threshold smell test, when using TON, is one of the numerous methods of arranging and presenting samples for scent determinations. The methods offered here are practical and economical of time and personnel. If extensive tests are planned and statistical analysis of data is required, more authentic methods similar FTT are performed.

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Alberta Oil Sands

R.J. O'Brien , ... A.H. Legge , in Developments in Ecology Scientific discipline, 2012

vi.7.two Potential Odor Compounds

Odors are probable, but not certainly, at this indicate to be caused largely past sulfur compounds. With this in mind, we accept compiled a listing of available candidate VOC and sulfur compounds from a critically reviewed assessment of odor thresholds past Devos et al. (1990). These are sorted by odor threshold in Figure 6.xx. Annotation that methyl mercaptan (methane thiol) has a threshold of 1   ppb; hydrogen sulfide has a threshold of virtually 12   ppb (vs. the Alberta Ambient Air Quality Objective of x   ppb), and, for reference, ethanol, at the very loftier level of 20   ppm.

Figure 6.20. A diagram listing the standardized human olfactory thresholds of selected compounds, which were summarized past Devos et al. (1970). The negative log of the concentration at which the odor is just detected past an odor console was determined past a weighted averaging of previous studies dating back over 100 years. Here, odor detection limits take been transferred to ppb.

Since January 1, 2012, a wide range of substituted thiophenes present during TRS episodes of 2   ppb take been measured and identified at the Bertha Ganter–Ft. McKay air monitoring station (Effigy 6.twenty). Individually, each compound is on the order of fifty ppt but in total they have ranged up to about 1   ppb at their highest. Interestingly, thiophene itself is never nowadays, and nosotros have not institute scent thresholds for substituted thiophenes. If collectively they have a similar threshold to thiophene itself, nosotros tin can correlate with the recommended threshold of Figure 6.20, which is virtually 200–300   ppb. It seems unlikely that these thiophenes are responsible for scent complaints. It is possible, nonetheless, from the GC/MS cartridge assay that other RSCs are present at concentrations somewhat lower than the thiophenes and are therefore not even so detected past the field PFGC. One such suspected compound is methylethyl-disulfide (tentative identification based upon retention time in GC/MS but not confirmed by spectral analysis). This compound's smell threshold is well below i   ppb. Further modest improvement in SCD sensitivity is recommended.

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Olfactory property generation and control

Arthur Thousand. Boon , Alison J. Vincent , in Handbook of Water and Wastewater Microbiology, 2003

3.5 Summary of control methods

Odour problems tin be minimized by:

1.

minimizing retention nether anaerobic conditions, including fugitive excessive aggregating of debris and grit in pipes, channels and tanks

2.

avoiding unnecessary contact of sewage and sludge with the atmosphere and minimizing turbulence

iii.

retaining malodours dissolved in solution until they can be biochemically oxidized naturally, eastward.chiliad. in an aerobic stretch of sewer, or in an aerated activated-sludge plant

four.

covering units and venting of independent air to an odour treatment unit of measurement

five.

addition of chemicals such as:

•

oxygen or nitrate to maintain aerobic or anoxic conditions

•

oxidant chemicals, such equally hypochlorite, hydrogen peroxide or potassium permanganate to reduce microbial action and oxidize previously formed sulphides

•

iron salts to precipitate sulphides. Iron salts are also used as a catalyst for the chemical and biochemical oxidation of sulphide

•

brine to convert H2South to HS− and Stwo−, the pH value should not exceed 8.5, to avoid release of alkaline odours (due east.g. ammonia, amines, skatole and indole)

•

specific inhibitors for sulphate reduction, these may be effective in the short term just, as adaptation of microbial species may occur.

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Effects on Health and Human Welfare

DANIEL A. VALLERO , in Fundamentals of Air Pollution (4th Edition), 2008

v. IMPACT OF ODOR ON HUMANS

Odors are perceived via the olfactory organisation, which is composed of 2 organs in the nose: the olfactory epithelium, a very pocket-sized area in the nasal organization, and the trigeminal nerve endings, which are much more widely distributed in the nasal cavity [11]. The olfactory epithelium is extremely sensitive, and humans often sniff to bring more than odorant in contact with this area. The trigeminal fretfulness initiate protective reflexes, such as sneezing or interruption of inhalation, with exposure to noxious odorants.

The health furnishings of odors are extremely hard to quantify, yet people have reported nausea, vomiting, and headache; consecration of shallow animate and coughing; upsetting of sleep, stomach, and appetite; irritation of the eyes, olfactory organ, and throat; destruction of the sense of well-existence and the enjoyment of nutrient, home, and the external environment; disturbance; annoyance; and depression [11]. Research under controlled conditions has qualitatively revealed changes in respiratory and cardiovascular systems. The difficulty has been in establishing the human relationship between the intensity or duration of the exposure and the magnitude of the furnishings on these systems.

People living in the plume of industries like coke ovens feel the obnoxious smelling compounds, including metallic and sulfur compounds that volatilize during the conversion of coal to coke needed for steel manufacturing. While such areas go along to exist industrialized, such ambient air quality equally that in the 1960s is no longer tolerated in the Due west. But such conditions do persist in some lower socioeconomic communities. In junkyards, for instance, the combination of fires, wet muck (comprised of soil, battery acrid, radiator fluids, motor oil, corroded metallic, and water), and oxidizing metals create a unique scent.

Odors have often been associated with public health nuisances. In addition to the link betwixt memory and olfactory centers, still, the nasalneural connexion is of import to environmental exposure. This goes beyond nuisance and is an indication of potential adverse health effects. For case, nitric oxide (NO) is a neurotoxic gas released from many sources, such every bit bars animal feeding operations, breakup of fertilizers after they are applied to the soil and crops, and emissions from vehicles. Besides being inhaled into the lungs, NO can reach the brain direct. The gas can pass through a thin membrane via the nose to the brain.

The nasal exposure is a different epitome from that usually used to calculate exposure. In fact, most risk assessment routines do not take a means for calculating exposures other than dermal, inhalation, and ingestion. People who live near swine and poultry facilities can exist negatively affected when they smell odors from the facility. This is consequent with other research that has found that people feel adverse health symptoms more than frequently when exposed to livestock odors. These symptoms include center, nose, and pharynx irritation, headache, nausea, diarrhea, hoarseness, sore throat, coughing, breast tightness, nasal congestion, palpitations, shortness of breath, stress, and drowsiness. There is quite a bit of diversity in response, with some people being highly sensitive to even depression concentrations of odorant compounds while others are relatively unfazed even at much higher concentrations.

Actually, response to odors can exist triggered past iii different mechanisms. In the beginning mechanism, symptoms tin be induced by exposure to odorant compounds at sufficiently high concentrations to crusade irritation or other toxicological effects. The irritation, non the scent, evokes the wellness symptoms. The odor sensation is merely as an exposure indicator. In the second mechanism, symptoms of adverse effects result from odorants concentrations lower than those eliciting irritation. This tin be owing to genetic predisposition or conditioned disfavor. In the third machinery, symptoms tin can result from a coexisting pollutant, e.chiliad. an endotoxin, which is a component of the odorant mixture. The multifariousness of health effects associated with air pollutants is vast. An understanding of the mechanisms and processes discussed in this chapter provides a foundation to hazard assessment.

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Volume 3

J.I. Blenkharn , in Encyclopedia of Environmental Health (Second Edition), 2015

Odour

Strong odours from healthcare wastes are not uncommon. Some medical laboratory wastes and wastes with a loftier proportion of faecal material such as incontinence waste and nappies, or urine bags, may smell strongly. Complaints regarding odour are not uncommon and at loftier ambience temperature, some wastes become especially pungent later merely a few days. More problematic but frequently overlooked are the warm, moist, shredded and compressed solid residues from ATT waste treatment processes. These may stand on site for many days, rapidly acquiring a new, rich and odiferous microbial flora comprising micro-organisms of environmental origin.

Refrigeration may help but consumes energy without much hope of lowering temperatures sufficient to reduce microbial action. A rapid turnround of wastes on a beginning-in outset-out ground is essential. Odour neutralizing products may help but are expensive.

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Air pollution control technologies

Daniel A. Vallero , in Air Pollution Calculations, 2019

13.10 Removal of odors

An odor can be described as a physiological response to the activation of the sense of smell [20]. It can exist caused by a chemical compound (east.g., H2S) or a mixture of compounds (eastward.yard., coffee roasting). Generally, if an olfactory property is objectionable, any perceived quantity greater than the odor threshold will be cause for complaint. The control of odors, therefore, becomes a matter of reducing them to less than their odor thresholds, preventing them from inbound the temper, or converting them to a substance that is non odorous or has a much higher scent threshold. Olfactory property masking is not recommended for a practical, long-term odor control organization.

thirteen.10.i Odor reduction by dilution

If the odor is not a toxic substance and has no harmful effects at concentrations beneath its threshold, dilution may exist the to the lowest degree expensive command technique. Dilution can be accomplished either by using tall stacks or by adding dilution air to the effluent. Tall stacks may be costlier if merely upper-case letter costs are considered, but they do not crave the expenditure for energy that is necessary for dilution systems. In addition, if the emission contains other pollutants, taller stacks will increment the distance traveled past the pollutant and, thus, will contribute to the long-range transport and the potential cumulative effects of these pollutants.

The aroma threshold for virtually atmospheric pollutants may be establish in the literature [twenty]. By properly applying the improvidence equations, one can calculate the height of a stack necessary to reduce the odor to less than its threshold at the basis or at a nearby construction. A prophylactic factor of 2 orders of magnitude is suggested if the odorant is especially objectionable.

Odor control by the add-on of dilution air involves a problem associated with the breakdown of the dilution organisation. If a dilution fan, motor, or control system fails, the odorous material volition be released to the atmosphere. If the odor is objectionable, complaints volition be noted immediately. Good operation and maintenance of the dilution arrangement become an absolute requirement, and redundant systems should be considered.

13.ten.2 Odor removal

It is sometimes possible to close an odorous system to prevent the release of the odor to the atmosphere. For case, a multiple-effect evaporator tin can be substituted for an open up contact condenser on a process emitting odorous, noncondensable gases.

Another possible solution to an odor problem is to substitute a less noxious or more acceptable odor within a process. An example of this blazon of control is the substitution of a different resin in place of a formaldehyde-based resin in a molding or forming process.

Many gas streams tin can be deodorized by using solid adsorption systems to remove the odor before the stream is released to the temper. Such procedures are frequently both effective and economical.

13.10.3 Odor conversion

Many odorous compounds may be converted to compounds with higher odor thresholds or to nonodorous substances. An example of conversion to another compound is the oxidation of H2Due south, scent threshold 0.v   ppb, to And then2, aroma threshold 0.5   ppm. The conversion results in another chemical compound with an odor threshold three orders of magnitude greater than that of the original chemical compound.

An example of conversion to a nonodorous substance would be the passage of a gas stream containing butyraldehyde, CHiiiCH2CHtwoCHO, with an aroma threshold of 40   ppb, through a direct-fired afterburner that converts it to CO2 and H2O, both nonodorous compounds. It should be noted that using a direct-fired afterburner, particularly ane without heat recovery, to destroy 40   ppb is not an economical use of free energy, and some other odor command system may be more than desirable.

This affiliate has introduced several examples and calculations of the theoretical basis for controlling and removing air pollutants. These are guidelines, but air pollution sources vary. The engineer and managing director must consider the specific atmospheric condition in selecting the all-time technologies to meet required emission limits.

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