**5. Conclusions**

The in-vehicle VOCs exposure is a public health concern worldwide. This study explored the thermal environment of an in-vehicle cabin under solar radiation and provided an early effort to quantify the spatial distribution of VOCs released from interior surfaces. In this study, the in-cabin thermal environment was simulated by considering in-cabin natural convection-conduction coupled with solar radiation. The performance of different combinations of turbulence and radiation models was validated with measured temperature data in a reduced-scale airplane cabin. Combining the SST k-ω turbulence model with a surface-to-surface radiation model (S2S) performed best in terms of computational accuracy among 30 different combinations, including turbulence models such as the standard k-ε, RNG k-ε, realizable k-ε, standard k-ω, SST k-ω and LES model and radiation models such as the P-1, S2S, DO, DTRM model. Our findings suggest that solar radiation plays a critical role in determining the temperature distribution in the cabin, which can increase as much as 30 ◦C for direct exposed cabin surfaces and 10 ◦C for shaded ones. The maximum average temperature was observed over 60 ◦C on the dashboard and rear board that were exposed the direct sunlight. The lowest temperature was found on the cabin floor at 44 ◦C. Such a high cabin temperature profile considerably lowers the thermal comfort and promotes VOCs emissions due to a strong temperature dependence. The dispersion of VOCs strongly depended on the local emission rate and airflows. The dashboard and rear board were shown to have a larger emission rate than that of the seats and floor because of the higher surface temperature. The VOC plume from the seats rose upward towards the ceiling, whereas the VOCs from the floor stayed below the seats. From the 2-h simulation period from 10:00 am to noon, there was a total of 35.08 μg VOCs and 19.02 mg TVOC accumulated throughout the cabin. With increasing attention to the cabin environment and the health of drivers and passengers, the findings, such as modeled spatial distributions of VOCs, provide automakers with an important design guide that could improve the current ventilation design for the summer time.

**Author Contributions:** H.L.: conceptualization, methodology, and writing—original draft preparation. Z.T.: methodology, project administration and writing—review and editing. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the National Natural Science Foundation of China (51708493); Zhejiang Provincial Natural Science Foundation (LR19E050002); the Zhejiang Province Key Science and Technology Project (2020C01111);

**Conflicts of Interest:** The authors declare no conflict of interest.
