Measuring and Modeling Surface Sorption Dynamics of Organophosphate Flame Retardants in Chambers

Understanding the sorption mechanisms for organophosphate flame retardants (OPFRs) on impervious surfaces is important if we are to improve our understanding of the fate and transport of OPFRs in indoor environments. Traditional Langmuir and Freundlich models are widely adopted to describe the sorption behavior of indoor semivolatile organic compounds (SVOCs). In a real indoor environment, it is possible that the sorption process of SVOCs on surfaces is more heterogeneous (multilayer adsorption) than homogeneous (monolayer adsorption). Therefore, interpreting the sorption mechanisms of OPFRs on surfaces using Langmuir’s equation may not be accurate. In this study, we adopt both Langmuir and Freundlich isotherms to characterize the adsorption/desorption dynamics of OPFRs on a stainless steel surface and make comparisons between the two models through a series of empty chamber studies. The chamber tests involve two types of stainless steel chambers (53-L small chambers and 44-mL micro chambers) using tris(2-chloroethyl) phosphate (TCEP) and tris(1-chloro-2-propyl) phosphate (TCPP) as target compounds. Test results show that the Freundlich model can better represent the adsorption/desorption process in the empty small chamber. Micro chamber test results show that both Langmuir and Freundlich models can well fit the measured gas-phase concentrations of OPFRs. We further apply the Freundlich model and the obtained parameters from empty small chamber test to predict the gas phase concentrations of OPFRs in a small chamber with an emission source. Comparisons between model predictions and measurement results show the reliability and application of the obtained sorption parameters.