Mechanism Of Impacting And Controlling Indoor SVOC Concentration

Indoor pollution caused by semivolatile organic compounds (SVOCs) severelythreatens people’s health. SVOCs include several classes of compounds such aspolycyclic aromatic hydrocarbons (PAH), phthalic acid esters as plasticizers (PAE) andpolybrominated diphenyl ethers as flame retardants (PBDE). These compoundshave relatively low vapor pressures, and readily adhere to indoor media such as PM2.5,resulting in ubiquitous exposure indoors. The exposure to these chemicals has beenassociated with cancer, bronchial diseases, reproductive harm and endocrine disorder. Aclear understanding of mechanism of impacting and controlling indoor SVOCconcentration is necessary to reduce health risk caused by exposure to SVOCs. Threekey processes (emission, transport and intervention) are closely relevant, but several keymechanism problems remain unsolved. For example, the uncertainy of y0, which is akey emission characteristic parameter, is unknown. A method to accurately describe thedynamic mass transfer between gas-and particle-phase concentrations is missing. Themechanism and effectiveness of influence of ventilation on indoor SVOC concentrationis unknown. Effective control of indoor SVOC pollution can be realized only after theseproblems are solved. The dissertation therefore presents studies on these aspects, withthe primary conclusions listed as follows:Firstly, a dimensionless mass-transfer model was developed to describe thebehavior of SVOCs in a ventilated chamber, which was usually used to study theemission characteristics of SVOCs. Based on this model, quantitative correlations wereobtained to instruct to improve the chamber design. Following the instructions, a newclosed-chamber method is proposed, which can avoid the artifact from wall-loss andhave improved economic efficiency. Experimental results show that for di-ethylhexylphthalate (DEHP, a typical plasticizer) in polyvinylchloride (PVC) flooring, theratio of y0to the vapor pressure of DEHP is0.74±0.10at23oC. Increasing themass fraction of DEPH in PVC from4.7%to23%results in an increase of y0byless than30%. These observations are preliminarily explained withthermodynamics of polymers. Stragegies to reduce measurement error wereproposed. These results provide guidance to predict and assess emission characteristics of SVOCs.Secondly, a generally applied dimensionless mass transfer model wasdeveloped to describe the dynamic mass transfer between gas-phase SVOCs andparticles. A characteristic parameter was identified to judge whether equilibriumcan be achieve between gas-and particle-phase SVOC concentrations: the ratioof equilibrium time to indoor residence time of particles. For particles with adiameter of2.5μm, the difference of predicted particle-phase SVOCconcentration is114%between the equilibrium theory and the dynamic theory.Based on the dynamic theory, a method has been proposed to predict the sizedistribution of particle-phase SVOCs. The secondary-source effect of particleshas been studied for the mass transfer between gas-phase SVOCs andsink/source surfaces. An underestimation of4times can be caused if thesecondary-source effect of particles is excluded to assess inhalation exposure toDEHP. These results provide theoretical basis to accurately predict SVOCconcentration and assess the consequent exposure.Finally, the influence of ventilation and particle dynamics on indoorairborne SVOC concentration is analyzed. The steady-state SVOC concentrationwould decease by37%, when ventilation rate is increased from0.6h-1to1.8h-1.In comparison, the averaged formaldehyde concentration would decrease by65%for the same change of ventilation rate as above. The impact of particledynamics on exposure to DEHP would decrease in the following order:deposition, emission, penetration and resuspension. These results helpeffectively control indoor SVOC pollution.