When Does Multiphase Chemistry Influence Indoor Chemical Fate?

Human
chemical exposure often occurs indoors, where large
variability
in contaminant concentrations and indoor chemical dynamics make assessments
of these exposures challenging. A major source of uncertainty lies
in the rates of chemical transformations which, due to high surface-to-volume
ratios and rapid air change rates relative to rates of gas-phase reactions
indoors, are largely gas-surface multiphase processes. It remains
unclear how important such chemistry is in controlling indoor chemical
lifetimes and, therefore, human exposure to both parent compounds
and transformation products. We present a multimedia steady-state
fugacity-based model to assess the importance of multiphase chemistry
relative to cleaning and mass transfer losses, examine how the physicochemical
properties of compounds and features of the indoor environment affect
these processes, and investigate uncertainties pertaining to indoor
multiphase chemistry and chemical lifetimes. We find that multiphase
reactions can play an important role in chemical fate indoors for
reactive compounds with low volatility, i.e., octanol-air equilibrium
partitioning ratios (Koa) above 108, with the impact of this chemistry dependent on chemical
identity, oxidant type and concentration, and other parameters. This
work highlights the need for further research into indoor chemical
dynamics and multiphase chemistry to constrain human exposure to chemicals
in the built environment.