Steady-State Based Model of Airborne Particle/Gas and Settled Dust/Gas Partitioning for Semivolatile Organic Compounds in the Indoor Environment

Indoor
semivolatile organic compounds (SVOCs), present in the air,
airborne particles, settled dust, and other indoor surfaces, can enter
the human body through several pathways. Knowing the partitioning
between gaseous and particulate phases is important in identifying
specific pathway contributions and thereby accurately assessing human
exposure. Numerous studies have developed equilibrium equations to
predict airborne particle/gas (P/G) partitioning in air (KP) and dust/gas (D/G) partitioning in settled dust (KD). The assumption that P/G and D/G equilibria
are instantaneous for airborne and settled dust phases, commonly adopted
by current indoor fate models, is not likely valid for compounds with
high octanol-air partition coefficients (KOA). Here, we develop steady-state based equations to predict KP and KD in the
indoor environment. Results show that these equations perform well
and are verified by worldwide monitoring data. It is suggested that
instantaneous steady state could work for P/G and D/G partitioning
of SVOCs in indoor environments, and the equilibrium is just a special
case of the steady state when log KOA <
11.38 for P/G partitioning and log KOA < 10.38 for D/G partitioning. These newly developed equations
and methods provide a tool for more accurate assessment for human
exposure to SVOCs in the indoor environment.