The olfactory mucosa is composed of the olfactory epithelium and the underlying olfactory neurons

In Denmark, both n-butanol and hydrogen sulfide are used to calibrate panelists, and the Japanese method uses five odorants in its panelist aptitude test . The use of multiple odorant standards may have advantages. Observations from related fields provide insights for environmental odor exposure assessment. Setting odor source minimum-distance setbacks and emission rates did not take into account the level of nuisance , so complaints continued . For the drinking water industry, analytical measurements and dilution-to-threshold limits did not resolve underlying taste-and-odor problems and correlated poorly with customer complaints .To save resources, risk assessment uses a screening-level assessment before a refined risk assessment is performed. The same approach works for odor exposure assessment and is practiced widely already. Two air inspectors, ideally, respond to a nuisance odor complaint so they can corroborate the complainant’s and each others’ sense. If corroboration occurs, the source of the odor is usually identified by the complainant or the air inspectors’ prior knowledge of the area. Standard practice is to move upwind of the identified source to confirm that the odor is not coming from elsewhere. Recording wind direction, details of the complaint and any action taken document the investigation.Training air quality inspectors on how to better identify describe odors might assist their work. For example, using an odor wheel and maintaining a log of complaints could identify trends. For many air districts, however,cannabis grow racks the ability to sense “something” in the air at the complainant’s location is sufficient. The odor intensity only need be noted as “faint” or “strong” to help prioritize the nuisance. Matching the complainant’s vocabulary of odor is unnecessary.

It is necessary for the air inspector’s sense of smell to be verified periodically. An anosmic air inspector, obviously, would be unfit for odor patrols. For difficult-to-discern odors, returning to the location several times may be required. Involving a panel of air inspectors should help detect odors that are especially low. The increased cost of a panel, and its training, would need to be taken into account.When a screening-level assessment fails to address an odor nuisance, more refined exposure assessment is necessary. Complexities such as overlapping odors, unknown sources and resistance on the part of the potential source to acknowledge responsibility can also require refined assessments. Refined assessments require more sophisticated documenting of the odor. The field assessments for plumes is a logical starting point. More subtle, ongoing odors require the grid approach . The various odor wheels included in Appendix A, in addition to the list used in Europe, help form a standard odor lexicon. Meteorological data factors into both of these odor-documentation techniques.If enough information on individual odorants within the environmental odor is available, such as through prior sampling of similar sources, then sampling of the odorous air may provide insights. Residential sampling using evacuated canisters has been successful, as long as container purges are performed and blanks are run in parallel. Trace analysis requires such. If air sampling bags are used, quality control samples must be included. Bag materials have been shown to adsorb certain odorants, allow them to escape, or sometimes contribute compounds to the odorant load. Figure 3.9 shows results for various bag materials spiked with ethylene . Greater adsorption has also been observed for certain odorants in Tedlar™ bags as compared to Teflon™ bags .Used in conjunction with analytical analysis of target odorants, especially by GC-MS-sensory techniques, OPM is a very useful tool to identify primary odorants and link them to their source.

Use of the OPM intensity results to derive ODTC50 and other low-intensity values, however, is suspect. A complete risk assessment acknowledges uncertainties and their effect on the results. A good odor assessment should do the same. Odor perception can be affected by many variables that are often uncontrolled, such as temperature, relative humidity, and even illness among panelists. From human factors to bag materials, all uncertainties and variability need to be acknowledged and, ideally, submitted to a sensitivity analysis to see how they affect the final results.Currently there is no international standard on how to respond to nuisance odor complaints, not even straightforward screening-level steps. International organizations such as Organization for Economic Cooperation and Development and World Health Organization focus more on health effects that nuisance complaints. Even fundamental sampling and analysis techniques have no agreed upon standard for environmental odors in ambient air. National and regional agencies have filled these gaps spottily. Once standards have been developed, they become entrenched and resistant to new, improved techniques. There is a clear need to develop standard methods for environmental odor monitoring in ambient air, combining both sensory and analytical methods. WHO recommends that future focus on perception of the actual odor rather than measuring individual odorants . Population dose-response measurements based on field studies are needed to build a fundamental knowledge base. Measures of “population annoyance” need to be developed, which Germany, the Netherlands and New Zealand are working toward . Quality standards, such as field blanks and spiked samples, are routine in air quality sampling and must be implemented in odor studies. Otherwise sample degradation, odorant loss or the introduction of unintended trace odorants is unknown. A compendium of sampling materials and their performance for specific odorants is needed. Basic research on odors will help advance the predictive power of analytical measurements.

Investigating and eventually being able to predict the synergistic, antagonistic, or masking interactions among odorants is especially important. Temperature and humidity effects are also a challenge requiring more research. The expansion of GC-sensory techniques and increased sensitivity, including greater use of SIFT-MS, will likely bridge the gap between sensory and analytical detection that exists today.Due to the complex physiological and psychological factors involved in human olfaction, the prediction of odor impact by e-noses will probably remain allusive. Nonetheless, closer approximation of human olfaction by sophisticated sensor arrays may reduce the reliance on human panels and offer continuous monitoring in the future. Machine learning is already being used to decipher human olfactory responses through the study of pattern-based odor detection and recognition, olfactory phenotypes, disease biomarkers, physicochemical properties that predict olfaction,cannabis grow system and public database mining .The World Health Organization defines health as “a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity” . Within this broad definition fall both the sensory and the non-sensory adverse effects of odors. To evaluate environmental odors, two approaches have been followed. The first approach is to trace the nuisance odor back to its source and take remedial action . The second approach is to apply the four steps of risk assessment to evaluate sensory and non-sensory risks posed by environmental odors. This second approach is followed in this paper. Risk assessment has its roots in the 1970s and in the 1980s began to bring order to an unmanageable amount of data on toxic chemicals and radiation in the hope to help regulators make better decisions . Through the 1990s, the field matured, especially under pesticide and Superfund site-remediation programs. Since 1983, the National Research Council has updated risk assessment guidance regarding the science, decision-making, and communication of risk , and the field continues to evolve. Risk assessment has broad acceptance in the United States and other countries, including Canada, Australia and Europe.A bit of confusion has occurred with the term “risk assessment.” Too often it is misused to mean just the estimation of the low-dose response following exposure to a carcinogenic chemical. That is the dose-response assessment, just one component of risk assessment. The term “risk assessment” is often confused with “risk management” as well. Risk assessment provides useful input to risk management but does not supplant it. Risk management involves policy, values and communication steps that go well beyond risk assessment . As practiced, risk assessments vary widely in scope and purpose. Some assess a single chemical across a range of exposure scenarios while others are site-specific and assess the variety of chemicals found at that particular site. In general, risk assessment is used to evaluate involuntary exposures. Voluntary risks are generally accepted by the public and receive less scrutiny .Risk assessment is central to this paper and will be applied through case studies rather than an assessment of a specific odor at a specific location using previously unpublished field data. Information on the health risks posed by odors, such as the case studies, was gathered through a literature search.

As a starting point, a previous risk assessment of odorants was augmented by a substantial review of the human health effects of odors by Alberta Health in Alberta, Canada . The 216-page review by Alberta Health included literature through July 2013. The present literature search was for documents published after this date, and the key findings of Alberta Health will be noted. The starting point for risk assessment methodology was the foundational work by the National Research Council , now updated for the 21st century . The programs that grew out of the original work have issued their own guidance, which was also consulted. Such programs include pesticides , site remediation , exposure factors and California-specific work . International efforts, such as the review of the chemicals in commerce in the European Union , were also consulted. The 1,556-page tome edited by Dennis Paustenbach titled “Human and Ecological Risk Assessment: Theory and Practice” was an additional starting point.Alberta Health critically evaluated over 500 peer-reviewed epidemiology and experimental studies on the impacts of odors on human health . The review not only examined the mechanisms by which odors induce a health response, but also identified effective risk-based approaches for regulating health impacts from exposures. The main outcomes of interest in the review were health symptoms, physiological responses, annoyance, mood and psychological health, quality of life, cognition , athletic performance, and brain activity. Alberta Health chose not to review animal studies, occupational exposures, hypersensitivity, commercial uses of aromas or potential systemic organ toxicity from odorant exposure. Of these gaps, occupational exposures are addressed in this paper due to their sentinel value for lower exposed residential populations. Non-sensory endpoints are addressed as well. Such information was found in other reviews and the post-2013 literature search.To understand the adverse effects from exposure to odors, the human sense of smell is introduced. Humans have around 5 million olfactory receptor neurons, and they are directly connected to the most ancient, primitive part of the brain. By comparison, dogs have around 220 million olfactory receptor neurons and rabbits have around 100 million. It takes around 1 second to respond to an odor. Olfaction relies on two neural systems and two routes of entry to the nasal cavity. Air enters either through the nostrils or the mouth . Volatile chemicals in the air bind to olfactory neuron receptors and to trigeminal neuron receptors . The combination of olfactory and trigeminal neuron receptors explains why menthol produces a minty smell as well as a tingling in the nose . The human nose contains roughly 400 different types of receptor neurons, each sensitive to specific types of odorants . The neural receptors signal the brain, which then associates the perceived odor with past experiences once the signal becomes strong enough. Environmental odors are typically a complex mixture of multiple odorants. The processing of odor mixtures involves activation of more brain regions compared to single odorants . Odorants can bind to one or more receptors, and receptors can bind to one or more odorants. Only a few odorants, however, are discerned within a mixture . Some odorants dominate while others are masked, and factors such as concentration, temperature and humidity all play roles.Human olfactory mucosa occupies 3% of the nasal cavity and is protected high in the nasal vault , so only an estimated 5 to 10% of air entering the nostrils reaches this region .See Figure 4.2 for an overview.When sensed orthonasally, odors are perceived as coming from the environment, while when perceived retronasally, they are perceived as coming from food in the mouth . Our two nostrils help us stereoscopically locate the source of the odor .