**5. Limitations of the Study**

Before coming to the conclusions, some limitations should be mentioned that need to be addressed in further studies. First, the sample size was sufficient to detect the association between n-butanol odor thresholds and the odor effects of another compound, but the sample was highly selective, and therefore, the transferability to the general population is somewhat limited. Here, a larger sample including older subjects, subjects with mild diseases of the upper respiratory tract (e.g., allergic rhinitis), and subjects reporting an increased odor sensitivity should be investigated. Second, the new method of the exposure lab-based threshold assessment should be tested with other odorants and compared to other threshold assessment procedures like squeezing and sniffing bottles [36–38] or the triangle bag method [39]. Third, odorants other and more pleasant than ammonia should be used to include the highly relevant dimension of pleasantness [40] into this branch of odor research.

#### **6. Conclusions**

The results presented here provide further empirical evidence that the olfactory sensitivity of an individual may be an important predictor of odor perceptions in near to realistic scenarios of the human odor experience. The reference compound n-butanol seems to be an adequate choice as shown by the good cross-method correlations. Nevertheless, the role of suprathreshold olfactory functioning such as odor discrimination or identification has not been conclusively studied in this context. Moreover, other reference compounds for panelist selection are currently under discussion (DIN EN 13725:2019) [41]. With respect to the impact of environmental odors on cognitive task performance, our results showed that "high odor sensitivity" was not associated with worse performance in a challenging working memory task. The results were opposite to a distractive effect of malodors as proposed previously [42].

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2073-4433/11/5/472/s1, Figure S1: Schematic overview of the experimental procedure during the exposure lab-based threshold assessment. Figure S2: Measured concentration values for n-butanol during the exposure lab-based threshold assessment. Figure S3: Schematic overview of the experimental procedure during the ammonia exposure (cf. [11,12]). Figure S4: Measured concentration values of ammonia during the experimental exposure. Table S1: Descriptive statistics for the total sample and subgroups.

**Author Contributions:** Conceptualization, M.P. and C.v.T.; methodology, M.P. and M.S.; validation, S.K. and M.S.; formal analysis, M.P. and S.K.; investigation, M.P. and C.v.T.; resources, C.v.T.; data curation, M.S.; writing—original draft preparation, M.P. and S.K.; writing—review and editing, M.P., S.K., M.S., C.I.H. and C.v.T.; visualization, M.P., C.I.H. and S.K.; supervision, C.v.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors would like to thank Meinolf Blaszkewicz, Nicola Koschmieder, Eva Strzelec, Michael Porta, and Beate Aust for technical assistance. The publication of this article was funded by the Open Access Fund of the Leibniz Association.

**Conflicts of Interest:** Marlene Pacharra, Stefan Kleinbeck, Michael Schäper, Christine I. Hucke and Christoph van Thriel declare that they have no conflict of interest.
