A version of this story by Dr. Shelly Miller is published in Public Lab's Community Science Forum, Issue 15. Photo courtesy of Dr. Shelly Miller.

Under-resourced communities often experience higher concentrations of air pollution and face greater risks of health problems. Odors from industrial sources is one type of air pollution that affects residents of these often-low-income communities physically and psychologically. North Denver, which is impacted by emitted odors from the surrounding industrial facilities, is one such example. Among North Denver neighborhoods, Globeville and Elyria-Swansea seem to be the most affected communities, where over 70% of their area contains commercial and industrial businesses, including Purina (a pet food factory), Suncor Energy (a major oil refinery), Koppers Inc. (a creosote wood treatment facility), Altogether Recycling, METech Recycling, Owens Corning Denver Roofing Plant, Owens Corning Trumbull Asphalt Plant, Metro Wastewater Reclamation District, Cobitco Inc. (an asphalt emulsion company), and DARPRO Solutions (a meat, grease, and cooking oil recycling facility). In addition to commercial businesses, Globeville and Elyria-Swansea are divided by major highways and railroad tracks.

Between 2004 and 2017, Denver received 1,322 odor complaints. In response to odor and health concerns, the City and County of Denver updated its odor ordinance in 2016, requiring some industries (e.g. pet food factories and marijuana production facilities) to develop Odor Control Plans (OCPs). The ordinance also extends the period in which complaints must be received for the City and County of Denver to trigger enforcement. The ordinance states that a facility that receives five complaints from individuals representing separate households during a period of 30 days will be required to develop an OCP.

In 2015, we completed a study specifically on asphalt odors in the Globeville neighborhood. An odor of unknown origin described as a “tar” or “asphalt” smell was reported as unbearable for many residents over the past few years, and caused burning eyes and throat, headaches, skin irritation, and problems sleeping. To identify the potential sources of the odor and the concentrations of air pollutants making up the odor, we collected wind speed and direction data and sampled for a suite of volatile organic compounds (VOCs), sulfur gases, and polycyclic aromatic hydrocarbons (PAHs) in the neighborhood and near suspected sources.

Wind speed and direction data indicated that when the odor was noticed, the neighborhood was directly downwind of a wood preservation facility and an asphalt roofing facility. Air samples collected during short-term, high-intensity odor events revealed strong concentrations of methylene chloride, hexane, toluene, naphthalene, dibenz[a,h]anthracene, benzo[g,h,i]perylene, and indeno[1,2,3-cd]pyrene—each at least two times higher than background concentrations. Naphthalene and the other PAHs are emitted from wood treatment processes and have a coal tar odor. Naphthalene was present in a sample collected directly adjacent to the Koppers creosote facility and was not present in any background samples. Single-compound odor and health thresholds, however, were never surpassed during our sampling. To follow up on this work, we conducted two additional studies in 2017 and 2018, in North Denver, and four similar communities in Colorado for comparison. In these studies, we focused on all reported odors and specifically on better understanding the effects on well-being.

Adverse health impacts are hard to investigate for a variety of reasons, including because health effects can be triggered at much lower concentrations than can be sometimes measured with analytical equipment, health data for many odorous compounds is outdated and missing, and impacts of mixtures of odor compounds are not understood.

We also developed a new method to identify the industry that most likely was causing the odors. The 2017 study assessed the impact of odors from industrial sources on the subjective well-being (SWB). An online survey was sent to participants from Greeley, Fort Collins, Fort Lupton, North Denver, and Pueblo, asking questions about SWB and odors in their areas; 351 people participated. The evaluation of SWB was performed using a novel approach that appraises three aspects and nine measures of SWB.

The results showed that participants who reported that the air is very fresh or the odor is highly acceptable had higher levels of SWB. This association suggests that residents who live in areas exposed to strong industrial odors had lower levels of SWB. A subset of participants in this study took the survey four times in one year. Both satisfaction with how life turned out and satisfaction with standards of living slightly increased during the fourth quarter of the year. A comparison between the five communities showed that well-being levels in North Denver and Greeley were not significantly different than those in Fort Collins or Fort Lupton. The comparison, however, showed that Pueblo had the lowest levels of well-being among all communities. In the 2018 study, a smartphone app was used to collect odor location and type of odor for more than one year. Spatial distributions of the odor data collected by social participation, combined with wind direction collected from local air monitoring stations, were used to identify odor sources in the impacted areas. The majority of odor complaints were reported in North Denver (57%) and Greeley (33%). North Denver analysis showed that a single facility that manufactures pet food was responsible for the pet food odor (the most reported odor: 81 reports). Dead animal and sewage odors were associated with a North Denver meat and grease recycling facility and the Metro Wastewater treatment plant, respectively. Roofing tar odor was probably associated with a facility that treats crossties and utility poles with creosote. Another odor that was often described as a refinery odor was less likely to be associated with the Denver oil refinery and more likely to be associated with one of the four facilities in the northwest of Globeville that uses asphalt and creosote materials. In the Greeley area, most complaints (133 reports) happened in LaSalle, a small town in the southern section. The analysis showed that all complaints from LaSalle described one offensive odor produced by a biogas facility to the east.

In summary, identifying sources of odor can be complex. Adverse health and well-being impacts are reported by many community members and yet quantifying these impacts and addressing them are often not undertaken by local or state officials. Many communities have inadequate odor plans and ordinances. Our studies in Colorado have identified methods that communities can use to collect data on sources of odor, adverse impacts, and odor types. These data, combined with wind data and other important information such as emissions databases, can be used to provide evidence of odor issues within the community. In addition, collecting odor data using methods like social participation is known to have a positive psychological impact on the studied community.

Dr. Shelly Miller is a professor of Mechanical Engineering at the University of Colorado Boulder and faculty member in the interdisciplinary Environmental Engineering Program at CU. She is currently working on research projects addressing indoor environmental quality, reducing building energy consumption, and identifying sources of air toxins and noxious odors in urban communities. She received M.S. and Ph.D. degrees in Civil and Environmental Engineering from the University of California, Berkeley.