Such risk assessment approaches can and have been applied to environmental odors. Unlike risk assessment of toxic chemicals, odor studies can include human panels. Risk assessment is directly applicable to the investigation of health risks from odors .The objective of this thesis is to conduct a critical literature evaluation, supplemented with interviews of odor experts and investigators, of scientific methods to investigate environmental odors and assess their health impacts. The overall aim is to improve the state of knowledge of a complex, multidisciplinary topic. In an effort to further advance the field of odor investigation, advice and concepts from the overlapping field of risk assessment will be applied, when appropriate. A review of the health impacts of environmental odors, which is information frequently requested by the public during odor investigations, concludes the review. The focus of this thesis is on nuisance odor investigations of existing facilities rather than predictive modeling used for permits of new or modified facilities. Much has already been written and reviewed on such predictive dispersion models and odor mapping . While such modeling is the most common approach, other approaches include maximum separation distance, maximum emission, plant grow table maximum annoyance and best technology requirements . It is likely that, in large part, the poor track record of these approaches has led to the need for nuisance odor investigations.
Indoor sources of odors are also beyond the scope of this thesis, as are occupational exposures to odors, except for the final chapter on health effects where the information is highly valuable for public health. Odors from emergencies and accidents are also not central to the thesis. The thesis is organized around increasing use of risk assessment to inform nuisance odor investigation. Chapter 2 on regulations and techniques used around the world to investigate nuisance odor complaints only employs some of the basic risk assessment concepts. Chapter 3 on odor exposure assessment falls within the risk assessment framework. Chapter 4 on the health risks from environmental odors is entirely consistent with and reliant upon risk assessment. Each chapter also identifies best practices, gaps in current knowledge and provides suggestions on how such gaps could be filled. Chapters 2 to 4 are presented as journal-ready publications. Chapter 5 ends the thesis with concluding remarks. Fugitive emissions from such industries can lead to odor complaints due to the extremely low sensory thresholds. Further, upsets and their associated larger releases are especially problematic at oil refineries , where it can take a long time to fix the problem. Historically, odors have been regulated under public nuisance law or when permitting a new or modified facility by conducting dispersion modeling within a theoretical odor impact assessment. The latter approach is outside the scope of this paper because it has been reviewed elsewhere . The use of dispersion modeling within a theoretical odor impact assessment has only achieved partial success as evidenced by the ongoing volume of odor complaints. Odor as regulated under public nuisance law for existing facilities, rather than proposed new or modified facilities, is the focus of this paper. Public nuisance law originated in British Common Law. Such law distinguishes between “private nuisance” and “public nuisance” . Almost always, nuisance odor complaints fall under the latter category rather than individual rights .
To address nuisance odor complaints, regulators may set subjective or objective standards. Based on population-based health studies of toxic air pollutants, objective standards have been set for pollutants. Odors, however, are multidimensional and require difficult-to-enforce standards. Unsurprisingly, the setting of odor standards varies greatly throughout the world and depends heavily on the industrial sector, type of activity generating the odor and level of public outcry. Applying public nuisance law to odors has been criticized : “A direct measure of annoyance is typically made by an inspector or authorized officer of the state, and if there are no complaints there is by definition, no problem. The inherent subjectivity built into the approach is a problem, as is its susceptibility to political influence or community pressure. It lacks continuity of regulation for both the community and the industry concerned and does not offer a ‘target’ for the design and management of odor control systems.” As an alternative, odor intensity limits have been set in some jurisdictions. Such limits remain sensory-based, bringing with them the inherent variability in human responses to odors, and typically are set at a certain number of volumes of odorless air required to dilute one volume of sample air until the odor is no longer detected by 50% of panelists . Dynamic dilution olfactometry, which requires a dilution instrument and evaluation by a trained panel, is typically used to set this limit.A team of Brazilian and Australian researchers published a recent, comprehensive review of odor regulations from around the world . Their survey of 28 countries primarily focused on the dispersion modeling and criteria applied to new and modified facilities emitting odorous gases. Such regulations typically set limits to emissions and setback distances based on the theoretical calculations of odor impact. They often also require that “best available technology” be implemented.
This regulatory approach is not the focus of this paper; nonetheless, the authors also covered, to a lesser degree, regulations and methods to investigate odor complaints from existing facilities, which have been tabulated .The U.S. federal government, under the Clean Air Act, does not regulate odors as airborne pollutants. That leaves odor regulation to the states. Odor regulations in 42 of the 50 states are addressed by nuisance law . The federal government, however, has provided general guidance regarding nuisance odors and their impacts . The National Research Council and the National Academies of Sciences, Engineering, and Medicine provide scientific guidance to the federal government. In the 1970s, the NRC pioneered guidance on odors . The conclusion was that odors would be difficult to regulate due to their variable adverse effects on people, standards would not be widely accepted and the two sets of data are difficult to relate toeach other, costly and time consuming. If enacted, odor standards would need to be related to a measurement of odor perception that is compared with the intensity of a specified concentration of a standard reference odorant. Duration and frequency of exposure, as well as offensiveness, should be considered. In 2014, the Agency for Toxic Substances and Disease Registry launched a web page to provide a series of documents and videos dedicated to environmental odor effects and management,hydroponic table including a reference list of 684 odorants and their sensory descriptors . For this list, ATSDR initially compiled a list of chemicals that the food and beverage industries use in production. ATSDR then added other chemicals that trained professionals or large numbers of people agree have a distinctive odor. Similar odor information has also been compiled by researchers into odor wheels . A distinctive odor can indicate the potential source and even the specific key odorants. This has helped solve odor complaint problems from landfills, trash transfer stations , composting facilities and wastewater treatment plants .Based on the information gathered from around the world, a targeted literature search and phone interviews of odor experts and air inspectors were conducted to provide current perspectives on odor investigations. Literature searches were conducted online and at the University of California, Los Angeles, and California Air Resources Board physical libraries. The focus was post-2010, and when relevant articles or books were found the “cited by” function was used to find even more up-to-date information. A California-specific literature search was conducted as well. Reviews of the latest approaches to odor investigation were sought. Finally, relevant websites and posted materials not typically available in scientific journals were searched.
To collect the latest information on nuisance odor investigations from California’s air districts and international experts, phone interviews were conducted. The interviewees’ insights were gathered and any available guidance documents and relevant case studies were requested.CARB has a long history of addressing nuisance odor complaints. In the 1970s, questionnaires were used to collect information from residents near pulp mills on exposure to the odor and on health and annoyance reactions . In general, the frequency with which odor was noticed and the frequency and intensity with which respondents were bothered by the odor were correlated with perceived odor intensity and frequency as measured by dynamic dilution olfactometry within each community. More recently, an agreement was formed between CARB and the local air districts regarding the handling of odor complaints . It stated that CARB handles mobile source odor complaints and, for stationary sources, the local air district is phoned as soon as possible, but at least within one business day. It then gives local air districts 15 working days after receipt of the CARB letter to provide a written complaint resolution or summary progress report. Finally, CARB agreed to subscribe to an over-the-phone verbal translation service that it would make available to the local air districts. Several of the local air districts were contacted to gather information on how they currently investigate nuisance odor complaints. The information gathered is summarized next. One observation during the interviews was that CARB trains the air district staff on smokestack opacity measurements using their own eyes . Training regarding environmental odor evaluation could be developed as well. A key phrase is “considerable number of persons,” which is evaluated case-by-case but generally falls into 6 to 10 complaints within a 24-hour period for a notice of violation. Rule 402 does not apply to agricultural operations. In 2008, SCAQMD Rule 410 took effect to address odors from trash transfer stations and material recovery facilities. Sufficiently large facilities were required to have an approved odor management plan with extra requirements for even larger facilities. In 2009, a panel of 10 air inspectors used odor profiling to evaluate a trash transfer station . Based on the observed odors, specific odorants were suggested and then confirmed analytically. In 2017, SCAQMD adopted Rule 415 to address odors from rendering facilities . The rule requires building enclosures with ventilation to odor control systems for odorous operations and best management practices, such as covers for trucks and trailers and time limits for moving materials during the receiving and rendering process. Also in 2017, Rule 1430 was adopted to reduce odors from grinding operations at metal forging facilities . Four confirmed odor complaints over six months trigger additional odor management controls, such as enclosures. A conversation with air inspectors covered how nuisance odor complaints are currently investigated. Air inspectors use their own noses to confirm the complaint, which does not necessarily need to match the complainant’s description of the odor. Each person’s ability to describe odors varies too greatly to require consistent descriptions. Rather, sensing that “something” is there is sufficient. The next step is to identify the source and move upwind to verify that the odor is not coming from elsewhere.They are trained on how to respond by pairing junior staff with more senior mentors. For more complex odors, monitoring and meteorological data are used. Hydrogen sulfide monitors have been used for direct measurements and SUMMA evacuated canisters and Tedlar™ bags have been used to collected air samples. Sometimes a SUMMA canister is given to a complainant to collect a sample over time. Wind direction, speed and temperature are measured using a hand-held Kestrel 1000 meter, and the cloudiness and weather are noted. More sophistical meteorological data has been used to calculate the back-trajectory of odor plumes using data from the National Weather Service in Meso West plus the HYSPLIT dispersion model. Odor investigation data is captured in an in-house database that is rather old and does not allow for easy queries. Since 2010, the number of odor complaints per year has risen from around 3,400 to 7,500, decreasing in 2017 to 6,000 . Odor complaints are received by phone or via their website, which is also available through their app.No electronic nose technology is currently used although a report surveyed dozens of emerging technologies . The authors noted that e-noses were primarily used for quality control for food and other products, and that a large effort would be required for field tests for environmental odor detection.