Partitioning of ROS from Lipid Film to DOS Film through Air

ZHENDUO YAO, Glenn Morrison, University of North Carolina at Chapel Hill

     Abstract Number: 388
     Working Group: Chemicals of Emerging Concern in Aerosol: Sources, Transformations, and Impacts

Abstract
The presence of peroxides, ozonides and other reactive oxygen species (ROS) has been observed on indoor surfaces. Initiated by ozone and possibly other oxidants, ROS has been shown to form on surfaces coated with skin lipids and cooking oils. Models predict that some of the ROS formed have physico-chemical properties that allow them to partition from indoor surfaces to aerosols. This process can thereby lead to inhalation exposure of indoor-generated ROS, and the possibility of deposition deep in the respiratory system. In this research, we explored the potential for ROS formed on indoor surfaces to partition via gas-phase transport to a separate condensed phase. A simulated surface lipid mixture (SLM), comprising squalene, fatty acids, triglycerides, and cholesterol was allowed to oxidize naturally on glass plates exposed to laboratory air for 5 days. After exposure, a second glass plate, coated with a thin layer of dioctyl sebacate (DOS), was placed over the SLM coated plate for 1 day. The SLM and DOS coated sides faced each other and were separated by a 1.0 mm air gap. The short distance allows for rapid transfer of semivolatile compounds from the aged SLM film to the DOS receptor film. The coatings on each plate were extracted and the ROS concentrations were measured using a colorimetric assay based on ferrous ion oxidation and xylenol orange as an indicator (FOX2 method). Preliminary results indicate that approximately 14% of ROS that forms in SLM partitioned to the receptor film. These experiments demonstrate that ROS formed within a reactive lipid mixture can partition from surfaces, through air to a separate condensed phase. Therefore, a considerable amount of ROS that forms on indoor surfaces should also be able partition to airborne particles.