Emissions of Volatile Methyl Siloxanes (VMS) from Vehicles

High Resolution Image Download MS PowerPoint Slide Volatile methyl siloxanes (VMS) are anthropogenic compounds widely used in personal care products and industrial applications and are frequently detected at elevated concentrations in urban air. However, their sources in urban areas remain poorly constrained. Here, we use chassis dynamometer experiments to quantify gas-phase VMS emissions from a range of on-road vehicles, including light-duty gasoline and diesel vehicles. Hexamethylcyclotrisiloxane (D 3 ) dominated the emitted VMS, over octamethylcyclotetrasiloxane (D 4 ), and decamethylcyclopentasiloxane (D 5 ). VMS emissions increased with driving speed and were substantially higher from gasoline than from diesel vehicles. Comparison with tunnel measurements showing elevated ambient VMS concentrations supports a significant contribution from traffic-related sources, including tailpipe and potentially nontailpipe emissions. These results identify vehicular emissions as a previously underrecognized source of VMS near highways, and provide new constraints for their atmospheric budget and source apportionment.