Follow your nose - Traveling the world of odorants in new cars

Injection artifacts in odorant analysis by gas chromatography

Odor-active compounds are major quality parameters in food and other consumer products. In the analysis of odorants, gas chromatography (GC) plays a dominant role and is particularly indispensable for odorant screening by GC-olfactometry (GC-O). Whereas artifact formation during workup before GC analysis has been widely discussed, artifact formation during GC injection has not been adequately addressed so far. Using a set of 14 test compounds, we evaluated ten different GC injection approaches. Artifact-producing reactions were particularly 1,2-eliminations. Linalyl acetate additionally showed [1,3]-sigmatropic shifts. On-column injection was confirmed as the gold standard, with virtually zero artifact formation observed not only with classic cold on-column injection in the oven, but also with on-column injection in a programmable temperature vaporizing (PTV) injector. Substantial artifact formation was observed when a high fixed injector temperature was combined with splitless injection. This applied to the injection of liquid samples but even more so to headspace solid-phase microextraction (HS-SPME) approaches. In conclusion, we recommend using on-column injection whenever aiming at a representative odorant spectrum, such as in GC-O. In targeted analysis, critical approaches such as SPME should be carefully tested for artifact formation. For the evaluation of the artifact formation potential of different injection approaches, cedryl acetate emerged as an excellent test compound.

Odour and indoor air quality hazards in railway cars: an Australian mixed methods case study

Purpose

This case study aimed to diagnose the cause(s) of a seasonal, and objectionable odour reported by travellers and drivers in the railway cars of Australian passenger trains. The research questions were to: (1) identify whether significant microbial colonisation was present within the air handling system of trains and causing the odours; to (2) identify other potential sources and; (3) remedial options for addressing the issue.

Methods

A mixed-methods, action research design was used adopted. Sections of the heating, ventilation, and air conditioning (HVAC) systems from odour-affected trains were swabbed for bacteria and fungi and examined for evidence of wear, fatigue and damage on-site and off-site. Insulation foam material extracted from the walls of affected trains was also subjected to a chemical assessment following exposure to varying humidity and temperature conditions in a climate simulator. This was accompanied by a qualitative sensory characterisation.

Results

Upon exposure to a variety of simulated temperature and humidity combinations to recreate the odour, volatile chemical compounds released from the insulation foam by water were identified as its likely cause. In addition, a range of potentially serious pathogenic and odour-causing microbes were cultured from the HVAC systems, although it is considered unlikely that bacterial colonies were the odour source.

Conclusion

The research has implications for the sanitising and maintenance policies for HVAC systems on public transport, especially when operating in humid environments. The sanitary imposition, especially in the wake of COVID-19 may be required to ensure the safety of the travelling public and drivers.

Concentrations of volatile organic compounds in vehicular cabin air - Implications to commuter exposure

In this study, 117 volatile organic compounds (VOCs) were identified and quantified inside passenger cars and buses operating city and intercity routes. The paper presents data for 90 compounds with frequency of detection equal or greater than 50% that belong to various chemical classes. Total VOC concentration (TVOCs) was dominated by alkanes followed by organic acids, alkenes, aromatic hydrocarbons, ketones, aldehydes, sulfides, amines, and phenols, mercaptans, thiophenes. VOCs concentrations were compared between different vehicle types (passenger cars - city buses - intercity buses), fuel type (gasoline - diesel - liquefied petroleum gas (LPG)), and ventilation type (air condition - air recirculation). TVOCs, alkanes, organic acids and sulfides followed the order: diesel cars > LPG cars > gasoline cars. On the contrary, for mercaptans, aromatics, aldehydes, ketones, and phenols the order was: LPG cars > diesel cars > gasoline cars. Excepting ketones that were found to be higher in LPG cars with air recirculation mode, most compounds were higher with exterior air ventilation in both, gasoline cars and diesel buses. Odor pollution, expressed by the odor activity value (OAV) of VOCs, was highest in LPG cars and minimum in gasoline cars. In all vehicle types, mercaptans and aldehydes were the major contributors to odor pollution of the cabin air with lower contributions from organic acids. The total Hazard Quotient (THQ) was less than 1 for bus and car drivers and passengers indicating that adverse health effects are not likely to occur. Cancer risk from the three VOCs following the order naphthalene > benzene > ethylbenzene. For the three VOCs the total carcinogenic risk was within the safe range. The results of this study expand our knowledge of in-vehicle air quality under real commuting conditions and give an insight into the commuters' exposure levels during their normal travel journey.

Smells like new car or rather like an old carriage? - Resolution of the decay behavior of odorants in vehicle cabins during usage

The typical new car smell is not only perceived directly after vehicle delivery. Vehicle interiors maintain their characteristic odors for a period of time during use even though the gas composition of the vehicle interior changes due to external influences. To obtain deeper insights into the odorant composition of a passenger cabin, this study aimed at characterizing the gas phase of two vehicle interiors at defined time intervals after vehicle delivery, and use by a customer in a controlled environment using a targeted odorant analysis. Thereby, the decrease in the general emissions in the cars did not coincide with the decay behavior of the odorants due to the chemical characteristics such as polarity of the odorants. Identification of the odorants in the vehicle interior during use revealed three groups of odor contributors exhibiting different decay behaviors: (i) odorants vaporizing rapidly via elevated temperature; (ii) odorants released by continued diffusion from materials; and (iii) fragrance chemicals of the customer. After 23 weeks of vehicle use, octanal, p-chloro-m-cresol, nonanal, p-tert-butylphenol, γ-nonalactone, and unsaturated aldehydes and ketones represented the most important odorants in the vehicle interior constituting the investigated car odor. The results of a descriptive sensory analysis corresponded with the identified odorants.