Odor emissions represent an increasingly significant social and environmental issue in Italy. The sources of these emissions are varied, but among the activities typically having the greatest impact are waste treatment plants, wastewater treatment plants, and companies in the agri-food, livestock, and chemical sectors.
“Odor emissions” refers to “channeled or diffuse emissions having effects of an olfactory nature,” thus referring to atmospheric emissions containing volatile substances capable of generating a perceivable and disturbing odor.
Although odors do not always constitute a toxicological problem—due to both their nature and their concentrations—the olfactory sensations and the annoyance they cause can lead to real health issues, such as headaches, gastric disorders, insomnia, and stress. This effectively compromises the quality of life for citizens and can potentially trigger legal disputes. But how is a “bad odor” evaluated and measured? The answer is complex and can be found in a combination of regulations, standards, and technologies.
Regulatory Framework
In Italy, the management of odor emissions is primarily regulated by Legislative Decree 152/2006, known as the Environmental Consolidation Act. Article 272-bis, which came into force on December 19, 2017, established the general principle and legal basis for managing odor emissions, defining a national reference framework but delegating to the Regions the authority and responsibility to define criteria, limit values, and technical specifications for activities generating odor emissions.
The Lombardy Region published guidelines for odor emissions with Regional Council Resolution no. IX/3018 of February 15, 2012 (General determinations regarding the characterization of gaseous emissions into the atmosphere deriving from activities with a strong olfactory impact). The guidelines adopted in Lombardy are considered the most complete reference regarding odor emission control. The document defines a technical approach for emission management through the use of dispersion models to predict olfactory impact and defines acceptability values expressed in ouE/m3. These values, calculated at the 98th percentile on an annual basis, serve as thresholds to be respected. The application of these directives is mandatory for new plants, while for existing ones, they are applied only in cases of “proven olfactory problems” reported by the population.
The Piedmont Region, with Regional Council Resolution no. 13-14554 of January 9, 2017, published guidelines for the characterization and containment of atmospheric emissions from activities with olfactory impact, developed based on those of the Lombardy region.
The Emilia-Romagna Region, with Regional Council Resolution no. 1495 of October 24, 2011, established a series of technical criteria aimed at reducing environmental impact in the design and management of biogas plants. these include the implementation of specific structural and management measures and introduce a mandatory odor emission monitoring plan for authorizations.
Similarly, in the Autonomous Province of Trento, the Provincial Council approved guidelines in 2016 for the “characterization, analysis, and definition of technical and management criteria for the mitigation of emissions from activities with olfactory impact,” following the model of the Lombardy Guidelines.
The Regional Law of Puglia (no. 32/2018) distinguishes itself from other guidelines by introducing olfactory impact criteria differentiated based on the sensitivity class of the exposed receptors. This approach classifies receptors into eight different groups, ranging from the most sensitive areas, such as those where hospitals are located, to those for industrial or agricultural use.
Dynamic Olfactometry according to UNI EN 13725
While the law established the need to measure and regulate, science provided the method. The UNI EN 13725 standard is the European technical reference for measuring odor concentration. At the heart of this protocol is dynamic olfactometry, the only regulatory recognized technique for quantifying odor concentration.
Dynamic olfactometry consists of determining the detection threshold of a gaseous sample taken from the source under examination. The process involves subjecting progressive dilutions of the sample to a panel of trained human examiners. The final result is the odor concentration in Odour Units per cubic meter (OU/m³), which corresponds to the number of dilutions required so that the odor is no longer perceived by 50% of the examiners.
