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Measuring and Modeling Surface Sorption Dynamics of OPFRs in Stainless Steel Empty Chambers
Citation:
Liang, Y., X. Liu, AND M. Allen. Measuring and Modeling Surface Sorption Dynamics of OPFRs in Stainless Steel Empty Chambers. Presented at ASTM SVOC Workshop, New Orleans, LA, October 12, 2017.
Impact/Purpose:
Understanding the sorption mechanisms for organophosphate flame retardants (OPFRs) on impervious surfaces is important to improve our understanding of the fate and transport of OPFRs in indoor environments. The aim of this study is to measure and characterize OPFR sorption dynamics on indoor impervious surfaces (e.g. stainless steel, glass and acrylic).
Description:
Organophosphorus flame retardants (OPFRs) are produced and used widely as alternative additives in building materials and consumer products such as spray polyurethane foam (SPF), polyvinyl chloride flooring, electrical and electronic products, furniture, textile coatings, and plastics. Due to their low volatility, these chemicals are classified as semivolatile organic compounds (SVOCs). Emissions of SVOCs from source materials usually occur slowly, and the gas phase SVOCs are readily adsorbed or absorbed by interior surfaces, airborne particles, and settled dust. Sorption to chamber walls can serve as significant sinks for SVOC emissions in chamber studies. The sorption process of SVOCs on surfaces involves heterogeneous (multilayer adsorption) and homogeneous (monolayer adsorption). Understanding the sorption mechanisms for SVOCs on the stainless steel chamber wall will improve the methods for measuring SVOCs emission rates and parameters that could be used for modeling the fate and transport of indoor SVOCs. We adopted Langmuir (monolayer adsorption) and Freundlich isotherms (multilayer adsorption) models, which are widely used to describe indoor sorption behaviors, to characterize the adsorption/desorption dynamics of OPFRs on stainless steel surfaces and made comparisons between the two models through a series of empty chamber studies. The tests involve two types of chambers, 53-L small chambers and 44-mL micro chambers, dosed by constant gas phase OPFRs. Stainless steel surface/air partition coefficients of OPFRs were obtained from the tests. 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 to predict the gas phase concentrations of OPFRs in a small chamber with a piece of SPF as an emission source. The study also illustrates that any test protocol for SVOC emissions testing must include characterization of the sink effect.