Modeling the reversible, diffusive sink effect in response to transient contaminant sources.

Area of Science:

• Environmental Science
• Indoor Air Quality
• Chemical Engineering

Background:

• Indoor air quality is influenced by volatile organic compounds (VOCs) emitted from building materials.
• Understanding the "sink effect" of indoor materials is crucial for predicting transient contaminant concentrations.

Purpose of the Study:

• To develop and apply a physically based diffusion model to evaluate the sink effect of indoor materials on VOCs.
• To predict transient VOC concentrations in indoor air under various emission scenarios.

Main Methods:

• A diffusion model was employed, assuming a homogeneous slab material and well-mixed indoor air.
• Model predictions utilized material/air partition coefficient (K) and material-phase diffusion coefficient (D).
• Three realistic building scenarios with time-varying VOC sources (styrene, phenol, naphthalene) and different materials (SBR, VF, PUF) were simulated.

Main Results:

• The model predicted varying sink effects: modest for SBR/styrene with continuous emissions, but significant for VF/phenol and PUF/naphthalene.
• Styrene butadiene rubber (SBR) considerably reduced peak styrene concentrations during an episodic spill.
• Parametric analysis showed that the equilibrium constant (K) governs profiles with high K, while the kinetic constant (D) dominates when mass transfer resistance is low.

Conclusions:

• Indoor materials exhibit a significant "sink effect" that modulates indoor VOC concentrations, with the impact varying based on material properties and emission patterns.
• The diffusion model provides a valuable tool for predicting indoor air quality and assessing the performance of materials as contaminant sinks.
• Material properties (K and D) and emission characteristics are key determinants of VOC concentration dynamics indoors.