A long-term dynamic model for predicting the concentration of semivolatile organic compounds in indoor environments: Application to phthalates

Semivolatile organic compounds (SVOCs) in indoor environments can partition into the gas phase, airborne particles, and settled dust and onto available surfaces. A long-term dynamic model was developed to predict the hourly concentrations of SVOCs over a year in the gas phase, airborne particles, and settled dust and on each sink surface. The model takes into account mass transfer mechanisms, the reactivity of SVOCs with oxidants indoors, and the influence of four indoor environmental factors (the air temperature, relative humidity, concentration of indoor airborne particles, and air exchange rate) on the mass transfer parameters. The model was validated for DEHP (di-2-ethylhexyl phthalate) and BBzP (butyl benzyl phthalate) by comparing the predicted concentrations in all the phases with the measured concentrations obtained in an environmental chamber and a test house. The model was then used to predict the hourly averaged concentration of BBzP in all the phases under real environmental conditions over a year. More than 52% of the variance in the BBzP concentrations was found to be associated with the covariance of the environmental factors. The air exchange rate explained at least 16% of the variance in the BBzP concentrations. In addition, the indoor air temperature explained 9% of the variance in the BBzP gas-phase concentration and the relative humidity explained 7% of the variance in the BBzP settled dust concentration. The variance in the concentration of the total suspended particles explained 10% of the variance in the BBzP concentration on the walls and windows.