Modeling the Fate of Oxidized Volatile Methylsiloxanes

Volatile methylsiloxanes (VMS) are known contaminants in the International Space Station (ISS). VMS have been detected in the gas phase, while some oxidized VMS such as dimethylsilanediol (DMSD) are found in the aqueous phase. Recent analyses have indicated that semivolatile or nonvolatile VMS oxidation products may form organic aerosols. In this work, the removal efficiency of oxidized VMS via various routes on the ISS is modeled in order to shed light on the potential for organic aerosol formation. Results based on estimated physical properties indicate that more than two sequential oxidations of a VMS lead to complete removal via humidity condensate. Partially oxidized VMS are also predicted to moderately partition to the airborne particle phase. VMS with one or two oxidations can thus be expected to play the largest role in aerosol formation as they are not efficiently removed via humidity condensate and may have a longer lifetime in the environment.