Odor pollution
Odor pollution refers to the presence of unwanted scents in the environment that can negatively affect people's quality of life. While many of these odors are nontoxic, they can still lead to significant discomfort and annoyance, making odor complaints a common concern in urban areas, particularly in Europe and the United States. Approximately 10 percent of Americans report experiencing issues related to odor pollution. The perception of what constitutes an unpleasant odor is influenced by cultural expectations, meaning that individuals from different backgrounds may react differently to the same smells. Identifying the sources of odor pollution can be challenging due to the complex nature of odors and the human ability to detect minute concentrations of certain chemicals, such as thiols and hydrogen sulfide, which are common culprits in various industries. Urban environments often face odor issues related to waste management, while agricultural activities may draw complaints from new residents in housing developments. Efforts to address odor pollution include citizen reporting systems and community task forces aimed at identifying and mitigating sources of unpleasant odors, as well as various industrial practices designed to minimize emissions.
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Subject Terms
Odor pollution
DEFINITION: Unwanted scents in the environment
Human beings are often annoyed by scents they find unpleasant or obnoxious. Although some odors signal the presence of hazardous air pollutants, many are nontoxic; nevertheless, their presence in the environment can have real impacts on quality of life.
Odor complaints are one of the top citizen pollution concerns in many cities in Europe and the United States; about 10 percent of Americans complain about odor pollution problems. The perception of odor pollution involves a combination of cultural expectations and the ability of individuals to perceive various odors. Cultural expectations play a strong role in reactions to particular odors. For example, people who travel outside their home countries may be exposed to olfactory experiences they consider highly unpleasant, while local residents remain oblivious to the same odors.
Malodorous substances and their sources are often difficult to identify and ameliorate. Because the human nose can detect tiny concentrations of certain chemicals, qualitative and quantitative analyses intended to identify malodorous substances are often inconclusive. Thiols rank high on the list of odor pollution complaints, which is not surprising given the widespread industrial applications of these chemicals and the human ability to smell minute concentrations. Ethanethiol is detectable by smell at concentrations as low as 1 part per 2.8 billion parts of air; much higher concentrations are needed for detection by standard chemical tests. The US Agency for Toxic Substances and Disease Registry (ATSDR) recommends citizens keep detailed "odor diaries" in the event of an odor pollution episode, as documentation of the offensive odor and its impact on health and daily activities can help local and state health agencies better identify the problem and develop solutions. The US Environmental Protection Agency (EPA) also developed a mobile app intended to allow people to classify and report odors, essentially using citizen science to harness the power of the human nose.
A variety of chemicals emanating from many sources often contribute to odor problems. Establishing a single cause for an odor is difficult because people who are able to identify a particular odor when it is found alone are often unable to identify it as a component in a complex mixture. Another factor is the of a substance, which may influence the acceptability of the odor. This is particularly true of indole, which is classed as pleasant-smelling in minute concentrations but is overwhelmingly unpleasant in moderate and high concentrations. Because indole is a product of tryptophan, which is used as a chemical reagent and in the manufacture of perfumes and pharmaceuticals, it is a potential odor in the vicinity of those industrial settings.
Throughout the United States, new housing subdivisions often encroach into areas that in the past were reserved for agriculture. In such subdivisions, recently transplanted urban dwellers may complain about a range of odors associated with farming activities, such as mowing hay and manuring fields. Solutions to this type of perceived odor pollution may include working to alter the expectations of new residents or recommending that they close their homes and use air conditioners rather than open their windows for “fresh air.”
Within cities, odor pollution is often caused by poor methods of disposal of garbage, including food residues. Large urban areas often develop task forces that combine the resources of a pollution-control office, a department, and refuse collectors to seek out and ameliorate the sources of bad odors. Past investigations of vile odors in San Francisco, California, identified the main culprit to be aging butter discharged into the sewer system by restaurants. The odors emanating from the city’s sewer system were eliminated by units similar to those used to clean up toxic spills, which removed the source of the stench and sprayed the area with disinfectant.
Many different industries have been identified as contributing to odor pollution, including food processing, paper manufacturing, electric power generation, and disposal. Pollution-control officers frequently find that similar manufacturing facilities have different odor problems. Apparently, differences in effluent gases from the facilities may produce differing odor strengths, resulting in different degrees of annoyance among nearby residents.
The kraft paper industry has received considerable attention for its emissions of highly odorous and unpleasant sulfurous gases. In the manufacture of kraft paper, hydrogen sulfide (H2S) is the major odor pollutant. However, the presence of enhances the unpleasant perception of H2S, which is more readily sensed in an acid gas mixture than in an alkaline gas mixture. Carbonyl sulfide (COS) and sulfur dioxide (SO2) also affect the perceived odor strength of the effluent gases. A kraft operation that controls the acidity of effluent gases may generate fewer complaints about odor pollution than the industry average. Asphalt plants are another notorious odor source. When these plants are fueled by recycled oil, both the energy source and the product may contribute to odor problems. One technique sometimes employed at these facilities is the use of odor-absorbing products to neutralize emissions of and sulfur dioxide.
An age-old practice for dealing with unwanted or unpleasant odors is to mask them with neutral or pleasant odors; for example, individuals may apply perfumes to cloak perspiration odor, and stores and offices may use “fresh scent” dispensers in their ventilation systems. Some industries have tried releasing masking odors along with known odor pollutants, with dubious success.
During atmospheric inversion conditions, all air pollutants increase in concentration, including odors. Transportation-related odors, including diesel and automobile exhaust, mingle with ozone created during photochemical smog. During these photochemical air-pollution episodes, the acrid odors signal a real public health threat.
Bibliography
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Drobnick, Jim, ed. The Smell Culture Reader. New York: Berg, 2006.
Godish, Thad. “Welfare Effects.” In Air Quality. 4th ed. Boca Raton, Fla.: Lewis, 2004.
"Odor Control." Agency for Toxic Substances and Disease Registry, 25 Aug. 2015, www.atsdr.cdc.gov/odors/odor‗control.html. Accessed 21 July 2024.
"Odor Explore: A Citizen Science Project Using a Mobile App and New Measurement Approaches." United States Environmental Protection Agency, 4 Apr. 2024, www.epa.gov/air-research/odor-explore-citizen-science-project-using-mobile-app-and-new-measurement-approaches. Accessed 21 July 2024.
Vallero, Daniel. “Effects on Health and Human Welfare.” In Fundamentals of Air Pollution. 4th ed. Boston: Elsevier, 2008.