Have you ever wondered about the mysterious smells surrounding us in indoor spaces? From the pleasant fragrance of freshly baked goods to the unpleasant stench of certain chemicals, odours play a significant role in our perception of indoor air quality. The German Committee on Indoor Guide Values (AIR) of the Ministry of Environment of Germany has delved into the science behind these odours and has published a final report on Odour perception thresholds for 20 Indoor pollutants in July.

   The ambitious project encompassed the evaluation of odour detection thresholds, odour intensities, and hedonic tone for 20 chosen substances present in ambient air. The substances ranged from familiar ones like acetone and acetic acid to less common compounds such as benzothiazole and ε-caprolactam. The idea was to gather more information to determine health risks of these substances.

   Indoor air is a relevant intake pathway for chemicals. The Committee on Indoor Air Quality Guidelines (AIR) sets health-related and hygienic guideline values that enable a health-related assessment of concentrations of certain substances present in indoor air in public and private buildings.

   The AIR consists of experts from the federal and individual federal states in Germany, which are named on the mandate of the Working Group of the Supreme State Health Authorities ( AOLG ). Additional experts can be appointed to work in the AIR.

   The AIR office is located in the Federal Environment Agency in Section II 1.2 "Toxicology, Health-related Environmental Monitoring ".

   The Council of Environmental Advisors (SRU) defines "indoor spaces" as:

•     Private dwellings with living rooms, bedrooms, hobby rooms, sports rooms, cellars, kitchens and bathrooms.
•     Workrooms in buildings that are not subject to the scope of the German Ordinance on Hazardous Substances with regard to hazardous substances, such as office rooms.
•     interiors of public buildings (hospitals, schools, day-care centres, sports halls, libraries, restaurants, theatres, cinemas and other public function rooms)
•     interiors of motor vehicles and public transport vehicles

   Today, people in Europe spend an average of 90 percent of their time indoors. Every day, people breathe in 10 to 20 m3 of air, depending on their age and how active they are. The indoor air we breathe can contain a variety of pollutants that can affect our health, and some of them also smell. We call those "odorants".

   Now, is there any guideline considering the impact of health of the odour in indour air? and I do not mean the toxicologic effect of the odorants but their effect on comfort and well living in indoor air. Well, the answer is yes, there are some guidelines around.

   In Germany, the first concept of "odour conductancy" was published by the German Committee on Indoor Guide Values (AIR) in 2014.In short, this guideline proposes a sort of two-level approach mulpliying the odour thresholds of a selected list of known indoor odorants by a number. This number depends on the relationship between the intensity and the concentration of the odorant, but takes also into account the hedonic tone. Also the concept of odour conductance considers some corrections factors sude to the "peak values" and the so-called "not directed attention".

   At the publication of this report of 2014,  deriving odour guide values was only possible for a few substances due to a few existing odour detection thresholds (ODT), which is why the Ministry decided to promote this new report.

   One of the core aspects of the research was identifying the odour detection thresholds (ODTs) for each substance. The OTV were determined according to EN 13725, and the intensities were determined with the resulting Weber-Fechner coefficients according to the German standard VDI 3882-1.

   Preliminary tests were conducted to ensure the accurate transfer of substances into the gas phase using the Olfasense Liquid to Gas Vaporiser (LiGaVa) method.

   To validate the results, the concentration of odorous substances was verified using FIS, GC-MS and GC-IMS at the nasal-olfactometer interface.

   The insights gained from this project will play a pivotal role in revising the evaluation scheme for future Odour Guide Values (OGV). By incorporating the determined odour detection thresholds, intensities, and hedonic tones of these substances, the revised concept by AIR will provide enhanced guidelines for assessing indoor air quality. In March of 2023 the AIR actually published a revised list of indoor air pollutants and their health thresholds.

   On page 24 of this report, you will find a summary of the works done in plain English.

   Download the report here (in German) or here (In English, automatic translation provided as a service of olores.org "as is")