New car odor: sensory and molecular characterization of odors and potential sources of smell in the vehicle interior

Abstract

The typical new car smell is very distinctive. Depending on vehicle brand and class, this characteristic odor differs in intensity and elicits either approval or rejection among vehicle purchasers. Up to now, only limited information has been available on the molecular composition of the new car odor. Vehicle manufacturers (OEMs) are mainly concerned with the analysis of toxic compounds and (odorless) main components of the gas phase of the vehicle interior. In addition, OEMs usually do not have an appropriate equipment to characterize odorants by instrumental analysis. Therefore, this work deals with the investigation of odors and potential sources of smell in the vehicle interior. In the first two chapters of this thesis, odor‐active compounds of an aqueous cavity preservation were analyzed by means of solvent extraction, gas chromatography‐olfactometry (GC‐O) and odor extract dilution analysis (OEDA). Odorants of the investigated corrosion inhibitor could enter the vehicle interior via air bridges between the vehicle body and the passenger cabin and could have a considerable influence on the odor. Identification of the potent odors by twodimensional gas chromatography‐mass spectrometry coupled with olfactometry (2D‐GC‐ MS/O) revealed a series of carboxylic acids and lactones as the main odor contributors of the cavity preservation. The hardening of the cavity preservation affected a change of the odor profile due to the evaporation of odor‐potent lactones which was confirmed by a descriptive odor profile analysis. A comparison with odorants of individual materials of the vehicle interior investigated in literature revealed that both identified substance classes are present in a wide variety of materials and, consequently, contribute to the odor in the vehicle interior. In the third chapter of this thesis, odorants of the aqueous cavity preservation were investigated by means of emission test chamber experiments with the aim to obtain further insights into the odorant composition. Since no appropriate method existed to investigate odorants in a gas phase in the form of a liquid odor extract, different sampling strategies, such as chamber air absorption and adsorption, were compared. Subsequent investigations by GC‐O and OEDA revealed potent carboxylic acids and lactones in the gas phase of the heated cavity preservation using each sampling method. In addition, more detailed results were obtained in a descriptive odor profile analysis by sample presentation of chamber air in odor bags compared to a presentation in glass vessels according to VDA 270. As a result, the developed methods may be extended for the investigation of odorants in air of big vehicle assemblies or whole vehicle interiors. In the fourth and the fifth chapter of this thesis, odorants of two new car interiors with different seat covers were analyzed as general proof of principle. For this purpose, air of the vehicle interiors was investigated in a whole vehicle test stand for interior emissions by means of adsorption and subsequent elution of the volatiles. Following GC‐O and 2D‐GC‐MS/O analyses, 39 odorants were identified belonging to various substance classes such as esters, saturated and unsaturated aldehydes, unsaturated ketones, rose ketones, phenol and benzene derivatives, and pyrazines. Furthermore, ten important odorants were quantified which could be detected in a descriptive odor profile analysis. After the initial investigation, both vehicles were used by a customer in his everyday life. At specific time intervals during use, the odorant composition of the vehicle cabins was analyzed by means of sensory evaluation and instrumental analysis after sampling on the test stand for interior emissions. The knowledge of the decay behavior of the odorants allowed further pinpointing of the most important odorants that caused the typical new car odor in the two investigated cars during vehicle usage. Based on these findings, a targeted investigation of individual components regarding the identified odorants and, thus, a reduction of the exposure to smelly substances in the vehicle interior will be significantly facilitated.