Particle/Gas Partitioning of Phthalates to Organic and Inorganic Airborne Particles in the Indoor Environment

The particle/gas partition coefficient K_p is an important parameter affecting the fate and transport of indoor semivolatile organic compounds (SVOCs) and resulting human exposure. Unfortunately, experimental measurements of K_p exist almost exclusively for atmospheric polycyclic aromatic hydrocarbons, with very few studies focusing on SVOCs that occur in indoor environments. A specially designed tube chamber operating in the laminar flow regime was developed to measure K_p of the plasticizer di-2-ethylhexyl phthalate (DEHP) for one inorganic (ammonium sulfate) and two organic (oleic acid and squalane) particles. The values of K_p for the organic particles (0.23 ± 0.13 m³/μg for oleic acid and 0.11 ± 0.10 m³/μg for squalane) are an order of magnitude higher than those for the inorganic particles (0.011 ± 0.004 m³/μg), suggesting that the process by which the particles accumulate SVOCs is different. A mechanistic model based on the experimental design reveals that the presence of the particles increases the gas-phase concentration gradient in the boundary layer, resulting in enhanced mass transfer from the emission source into the air. This novel approach provides new insight into experimental designs for rapid K_p measurement and a sound basis for investigating particle-mediated mass transfer of SVOCs.