Impact of Indoor Environmental Parameters on Formaldehyde Concentrations in Unoccupied Research Houses

An environmental parameters study has examined the impact of indoor temperature (T) and relative humidity (RH) levels on formaldehyde (CH₂O) concentrations inside two unoccupied research houses where the primary CH₂O emitter is particleboard underlayment. The data were fit to a simple three-term, steady state model describing the T and RH dependence of CH₂O concentration in a single compartment with a single CH₂O emitter. The model incorporates an Arrhenius T dependence and a nonlinear RH dependence of the CH₂O vapor concentration within the solid CH₂O emitter. The RH dependence is based on Freundlich's theory of the adsorption of water vapor on solid surfaces. The model is used to estimate potential seasonal variation in CH₂O concentrations under specified experimental conditions inside the research houses. The modeled results indicate six- to ninefold variation between 18°C, 20% RH and 32°C, 80% RH, simulating potential winter/summer conditions with minimal indoor climate control. In comparison, Indoor conditions ranging from 20°C, 30% RH to 26°C, 60% RH yielded approximate two- to fourfold fluctuations in CH₂O concentration.

The research house data were also used to evaluate the limitations and applicability of more complex five-term models developed from small-scale chamber studies of the environmental dependence of CH₂O emissions from particleboard underlayment. These models also incorporate a linear T and RH dependence of the CH₂O transport rate through the CH₂O emitter in addition to the T and RH dependence of the CH₂O concentration within the emitter. Good correlation is observed between the results of the research house studies and 1) a selected (i.e., single) underlayment model over a broad range of environmental conditions and 2) a combined underlayment model over a restricted range of environmental conditions.