Volatile methyl siloxanes in electric vehicle cabin air: The first investigation of occurrence, influencing factors, and inhalation risks.

Volatile methyl siloxanes (VMS) are synthetic chemicals extensively used in various components of electric vehicles (EVs). However, their release characteristics in EV cabins and the potential inhalation risks to occupants remain unclear. This study presents the first investigation of 13 VMS (7 linear VMS (lVMS) and 6 cyclic VMS (cVMS)) in EV cabin air. The impacts of vehicle usage parameters and cabin environmental conditions were also assessed to identify dominant influencing factors governing VMS contamination. All target VMS were detected in air samples, with 11 present in over 65 % of the samples. Notably, 3 regulated VMS (octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6)) were the most abundant, averaging 1978-3060 ng/m³ and collectively constituting 54.2 % of total VMS. Correlation analysis, Generalized Additive Model and two machine learning models revealed that environmental conditions exerted more pronounced impacts on VMS contamination than vehicle usage parameters. Specifically, lVMS and cVMS levels were governed by temperature and relative humidity, respectively. Although over half of VMS had significantly higher concentrations in private vehicles compared to ride-hailing vehicles, the estimated daily inhalation exposure for ride-hailing drivers was an order of magnitude higher than that for the general population, suggesting potential health risks for this occupational group. These findings provide critical insights into VMS contamination in EV cabins and highlight the necessity for enhancing regulatory measures and technological interventions to mitigate occupant exposure.