Odors are the result of a specific sensory response when olfactory cells in the nose are stimulated by particular chemicals in gaseous form. Odors can be generated from a variety of natural and human-caused processes and activities, from the scent of pine trees and blueberry muffins to the smell of manure and chemicals from manufacturing.

Odorous gases can be measured either directly or through gas surrogates. While our ability to measure odor has improved over the last several years, there are still difficulties in matching “annoyance level” of a particular odor to a measured concentration across a diverse population. As a result, it is not possible to adopt a state ambient air quality odor standard. Despite this, odors can be a source of private or public nuisance. The MPCA provides limited technical assistance to any local unit of government attempting to address an odor issue.

Using a nasal rangerOdor is rarely useful in determining a human health risk. Not all unpleasant odors are human health concerns. At the same time, many unhealthy chemicals have no odor. In some limited circumstances, however, a facility that reduces its emissions of certain chemicals may also reduce neighborhood odor. In these rare cases, the MPCA may be able to use odor measurement as a surrogate for specific chemical concentrations. Generally the MPCA will address health concerns by considering the primary pollutants, with odor reduction a by-product of reducing those pollutants.

Odors associated with farm animal production and feedlots can sometimes be handled through hydrogen sulfide rules. Farm and feedlot odor questions should be directed to the MPCA feedlot program.

Complaint referral

Odor complaints are handled on the county or local level, since there is no state odor rule. The first thing to do is identify where the odor is coming from. The figure below illustrates a common path. It is not necessarily the only way to address odor concerns, but the figure identifies main process that need to be considered.

Odor-control process: 1. Observe odor; 2. Identify source; 3. Determine reasonable plan; 4. Maintain compliance plan

Who to call when you are concerned about an odor

City. Although most cities do not have specific odor rules, your city offices are one of the best resources available for odor regulation. Odors can be considered nuisances. Companies are generally willing to cooperate on nuisance issues with the city because of the need for city permits and approvals on other matters.

County. County officials, such as hazardous waste staff, can be helpful by inspecting for chemical odors. In the past, for example, county hazardous waste officials have investigated odor complaints regarding spray booth operations.

Company. Some companies are very responsive to their neighbors’ concerns. It can be difficult for a citizen to call a neighboring company and discuss odors, but if the company is willing to be a good neighbor, it may be possible to resolve odor issues without involving a regulatory agency.

State. The MPCA does not have a state odor rule, but sometimes odors can be an indicator of pollutants that have emission limits. In some cases, odor is detectable even when a company is within its emission limits; in that case, although the state has no regulatory recourse the case can be referred to city and county officials to ensure the facility is in compliance with local rules. You may call the MPCA to file a complaint. Staff will follow up all complaints to discover if a permit limit is being exceeded or if the company does not have an appropriate air emissions permit.

If you have information concerning an observed pollution problem, we strongly encourage you to submit it to the MPCA using our online Citizen Complaint form, or register your complaint by calling the Air Quality Complaint Line: 651-296-7300.

Technical information and reports

PDF icon A detailed assessment of the science and technology of odor measurement

The basics of measuring odorous air which includes a brief explanation of nasal anatomy. The applicability and cost of laboratory olfactometry is discussed along with a description of odor panels. This detailed report identifies international standards for odor measurement and model odor regulations as well as standardized odor measurement techniques. It also introduces the subject of community odor studies and outlines several odor study methods including a case study involving a community odor survey. (St. Croix Sensory Inc., 2003)

PDF icon A review of national and international odor policy, odor measurement technology, and public administration

This report was prepared at the direction of the MPCA to present the current state of the practice in odor regulation in the United States and selected countries, review the common regulatory needs and suggest a regulatory framework. The report provides an overview of odor and its effects as well as odor measurement and regulation in Minnesota. It also includes the results of a county odor survey, a review of various odor regulatory methods, and a model odor regulatory framework. (2004)

More information

Some odor issues are resolved by venting emissions at different times of the day, when fewer people are exposed to an odor; others can be controlled by re-routing smelly gases through a pollution-control device. For odor concerns contact your local city or county for additional information.