Two major case studies from SCAQMD are informative. The first case is metallic odors in the industrialized section of the City of Paramount that began in 2013 . Nickel and hexavalent chromium were detected in air samples. Three businesses with metal-related operations were identified and many community meetings were held to address both odor and air toxics concerns. Under an Order for Abatement, one company was required to take measures to reduce odors in July 2017. They improved air pollution controls in their grinding room and made other improvements, and the number of odor complaints decreased. The second case is the coastal area of Seal Beach, Huntington Beach, and Long Beach that experienced “gas/sulfur/chemical” odors . To help find the allusive source, sampling was performed between March 2017 and October 2018 in partnership with local fire departments. SUMMA canisters were analyzed for the presence of volatile organic compounds, and samples collected in Tedlar™ bags were analyzed for total reduced sulfur compounds. Crude oil was the likely source of the compounds detected, and in October 2018 a violation was issued to an oil tanker that, upon inspection, had 7 out of 10 pressure release devices leaking . Portable hydrocarbon-sensing devices and gas imaging cameras were used to detect the leaks. Monitoring for other sources using a forward-looking infrared camera and further sample collection are ongoing. To address the beach communities’ health concerns from the intermittent exposures,grow rack and to put the monitoring data into context, a “frequently asked questions” document was created .

The conclusions were that the levels of hydrogen sulfide were below the 30 ppb one-hour state standard, the levels of specific hydrocarbons were below their acute limits, and that cancer risk was not at a level of concern due to the intermittent nature of the exposures.The Bay Area Air Quality Management District , headquartered in San Francisco, sets an odor limit of 5 dilutions-to-threshold at or beyond the facility fenceline, which is applied after at least 10 complaints are received within a 90-day period . Further investigation is required if a further 5 complaints are received within the next 90 days. Interviews with staff provided recent information and insights into investigation techniques currently used. Although still found in their local regulations, the use of odor panels to evaluate samples captured in bags ended over five years ago. The primary concern was that employees, who served as the panelists, were worried about exposures to unknown compounds and experienced negative sensations. Using air monitoring results for specific odorants and comparing the concentrations to odor detection threshold concentration was considered not in line with odor being a sensory nuisance . Lacking any quantifiable sensory method, air inspectors now conduct source-by-source investigations using their own sense of smell with moderate success. An inspection is triggered when 5 or more independent complaints are received and can result in a Violation Notice. Although their “Odor Policies and Procedures” is currently being revised, BAAQMD has several experiences worth sharing. When an odor complaint is received during office hours, within 15 minutes it is assigned to an air inspector who has 30 minutes to contact the complainant.

They then meet, experience the smell together and walk toward the source together. No sensory descriptors or training are used. They also explore upwind. If the odor is verified, the source is contacted and, if needed, inspected to see if in violation of the permit.A database developed in-house manages the case load. Regarding odor management plans that facilities have submitted, the air inspectors found substantial difficulties. Such plans are difficult to enforce, different for each site, written by a third party , and require large amounts of staff review time. Regardless, they are commonly found at WWTPs and trash transfer stations. A prior contract with Envirosuite Inc. was not continued due to the substantial requirements for meteorological data. The project tried to use advanced backtracking technology, based on real-time fine-scale meteorological modelling, to instantly plot and visualize the trajectory of an odor complaint, thereby identifying its likely cause. A current challenge is the overlapping odors found in Milpitas, which have resulted in thousands of complaints. To fingerprint and identify which sources are contributing to the ongoing odors, BAAQMD issued in March 2019 a request for proposals . A community group that meets quarterly is conducting a parallel study. Another challenge is the increase in composting operations, which are often malodorous. Finally, an emerging area of concern is cannabis cultivation, particularly within and around Santa Rosa, California. To understand the operations, BAAQMD staff toured a cannabis cultivation facility and will visit again.To become a “verified complaint,” air inspectors from the Sacramento Municipal Air Quality District rely on the definition of nuisance being about the complainant’s perception and try to verify that. Upon meeting the complainant, the air inspector logs their own description of the odor and sees if it matches that of the complainant. Standardized smell vocabulary would be useful.

A verified odor nuisance can lead to a Notice of Violation, which in turn can lead to an Abatement Order that shuts down the facility. The owner must then sue to reopen the facility. SMAQMD is considering trying a field olfactometer like neighboring air districts have. Previous tests conducted at the source of an odor need to be translated to fenceline concentrations experienced by the neighborhood. A current challenge is a rendering facility. California law, the Right-to-Farm Act, exempts such facilities from nuisance law, however. Another challenge is a sweet potato drying operation that has rotting odors. Also, the Zero Waste initiatives are sending more scraps to compost facilities, which are exempt from air regulations, so solid waste programs handle the complaints . Even pleasant aromas can become nuisance odors. A blueberry smell from a food factory was intense enough to trigger migraines. Masking has been done using cherry “perfume” at a solid waste landfill. Complaints are logged into a database that contains over 13,000 records since 1996. The data was transitioned from MS Access to MS Share point,microgreens shelving which sends automated e-mails and allows for logging from the field.Air inspectors from Placer County Air Quality Management District respond to all odor complainants. They drive to the complainant and try to verify the odor, even if they need to wait for an intermittent odor. If detected, they then try to identify the source. No cases have ended up in court, just resolved by mutual settlement. Past experience with a field olfactometer was not helpful due to the transient nature of most odors. The major source of odor complaints is a landfill. The dispersion modelling was not helpful, and sampling was sent for odor intensity testing by a panel. A spray coating did not stop the odor, nor did a cherry/citrus mist at the perimeter. The latter actually magnified the odor. Another nearby source, bioenergy wood piles, was blamed for the odors by the landfill.The San Joaquin Valley Air Quality Management District covers eight counties. Once a complaint is received, the air inspector visits the complainant to determine the type of odor, time of day and GPS location. Driving around, the source is identified. If the source is a permitted facility, the air inspector goes on-site to review the permit and inquire about any upsets or disruptions. If not permitted, the air inspector talks with the source and offers compliance assistance and education. The air inspector always circles back to the complainant to communicate the findings. A senior air inspector often accompanies a new inspector to provide mentoring. Once source of odor complaints was from residents who disagreed with urban planning decisions. Other complaints were from a WWTP that had a pond go anaerobic and a rendering plant, which is now closed. Their database could serve as a model for other air districts. It was developed in-house, which was expensive, but the functionality is impressive.

The database is on-line, smart phone friendly, interfaces with their app and, thus, can collect photos and videos. The system sends automated notifications to inspectors by text or e-mail. It also includes mapping features.Air inspectors find it sufficient to use their own sense of smell to verify odor complaints and try to respond to each call . Their familiarity with the local sources helps resolve most issues . Both field dilution measurements and laboratory panels did not aid investigations, nor did traditional dispersion modeling . The use of standardized odor descriptions may help inspectors , but agreeing with the complainant on the description is unnecessary. Masking odors to cover up malodors can magnify the problem . The FIDOL framework or a variation thereof is used by many jurisdictions. It is sometimes incorporated into guidance for complainants, too. The terms cover the main contributing factors or nuisance odors, namely frequency , intensity , duration , offensiveness , and location . FIDOL fails to capture, however, some of the more personal aspects of odor perception. The underlying mood and coping strategy of the complainant are missed, as is any connection or history with the offending source. The person’s history and susceptibility to malodor effects – such as age, sex, and health – are not included, nor is past experience with the same or different odors, which can lead to sensitization or trigger memories. These factors, which serve as confounders to odor investigations, relate to properties inherent to odor yet not present for classical air pollutants . FIDOL also neglects the number of people impacted. The main weakness may be in the variability inherent in two of the factors: intensity and offensiveness.Jurisdictions tend to use the same database software to manage odor complaints as they do for any air pollution concern. Development is typically through software vendors but may be done in-hose if sufficient funds are available . Such data is valuable for tracking trends in odor complaints. More sophisticated evaluations than the number of complaints are needed, however, to capture the actual impacts. Software vendors also support facilities so they can manage complaints in-house and track their own data. Such systems are required in certain jurisdictions, such as Colorado. In addition to time trends, a complaints database can be analyzed statistically or visually. For drinking water, six utilities were included in a study of customer complaints . The data were evaluated using several statistical methods, and the same could be done for done for an odor complaint database. A combination of high frequency of complaints together with consistency of descriptors was indicative of episodic water quality problems. Another way of analyzing odor complaint data is through a “word cloud,” as was done for a chemical spill in a river . See Figure 2.3 for an example where the size of the font indicates word frequency.The objective of this paper is to gather and review the technical approaches currently used to measure and monitor exposures to environmental odors. The technical approaches from around the world will be evaluated from a scientific standpoint as well as by applying practices from risk assessment, its framework and conventions, where appropriate. The goal is to identify best practices, identify any gaps and suggest how such gaps could be filled. The ultimate finding would be a universal approach that can be used for any odor complaint. This requires integrating disconnected research fields, not unlike the risk assessment of exposures to toxic chemicals has attempted. Investigations of nuisance odor complaints are the focus of this paper rather than predictive emission and dispersion modeling used to grant industrial facility permits. Some overlap between methods, however, exists.Odors are complex mixtures that evoke complex responses. There is no single parameter that completely characterizes the exposure to and impact of an odor . Unlike vision and hearing, the language of odor perception is poorly developed. Some people have a sense of smell that is orders-of-magnitude more sensitive than others, and the offensiveness of a smell is highly personal and culturally based. Even the microbes living in the nasal cavity can influence a person’s sense of smell . Such variability applies equally to air inspectors as it does to the general public.