# The Ability to Control VOC Emissions from Multilayer Building Materials
## 1 Introduction
### State of Knowledge-Emission Modelling
These entities and activities are then organised temporally and spatially in such a way as to give rise to the overarching behaviour of the mechanism [25].The project considered the problem to provide a comprehensive set of data and tools whereby buildings indoor environmental conditions can be optimised. Research teams of [PERSON] et al. [20] developed a procedure for estimating the mechanistic emissions model parameters using VOC emission data from standard small chamber tests. In the second group of models presented in the literature (see Figure A1, Appendix A), models are also presented, partly based on the theory of mass transfer, but these are specialised models of VOC emissions from systems of multilayer building materials; these systems in our research report are very important because the subject of these studies were multilayer sets of products-emitting VOCs, representing as faithfully as possible the practical sets of floor layers. Although our discussion's subject is currently emission models from multilayer systems, the researchers from Lawrence Berkeley National Laboratory, [PERSON], [PERSON], [PERSON] [26] should be considered a precursor. However, their research is limited to providing the captured elapse time emission curves of several compounds. Such tests were performed by observing the emissions from one layer of solid material (in this case, a carpet), but in fact, it was a two-layer system in which the double layer was represented by material/air interface. As a result of this work, volatile VOC emission profiles from several new carpets were recorded. More comprehensive was the research carried out at Concordia University by [PERSON], [PERSON] [27]. Their scope can be included in the same group of observation of phenomena, although there is a reference to the physical model according to [PERSON]'s second law and the related need to diversify the description of emission phenomena:  
\[\frac{\partial C_{a}}{\partial t}=D(\
abla^{2}C_{a}) \tag{2}\]  
where \(\delta C_{a}/\delta t\) is a rate of change in the concentration of compound \(a\) (mg/m\({}^{3}\) h\({}^{-1}\)), \(D_{m}\) = diffusion coefficient (m\({}^{2}\)/h) and \(\
abla^{2}\) = the Laplacian operator of \(C_{a}\) (concentration of compound \(a\) in the overlying air (mg/m\({}^{3}\)). Each compound under given environmental conditions has its own diffusion coefficient, depending on its molecular weight, molecular volume, temperature and the material's characteristics within which the diffusion occurs. [PERSON] and [PERSON] [28], followed by [PERSON] [29] and [PERSON] et al. [30], continued their work, now on a physical model of a multilayer material based on the theory of mass transport, although, according to other authors [31; 32], it is not possible to develop such a model. This would be a model from which the final concentration of VOC emitted from the surface of a multilayer sample could be determined by simply superimposing the concentrations of pollutants emitted from the individual layers of building materials. This is not possible because the model uses four parameters specific to each material of each layer: the diffusion coefficient of each material layer (\(D_{m,i}\)), material/air partition coefficient for each material layer (\(K_{ma,i}\)), initial concentration in each material layer (\(C_{0,i}\)) and convective mass transport coefficient (\(h_{ma}\)). Such a model would ignore the phenomenon of mutual suppression of VOC diffusion through layers. The models are to be used to predict the rate of VOCs emission from a multilayer material: the rate of VOCs absorption by the material, the concentration of VOCs in the air, both emitted from VOC sources and materials post-adsorbing (sink) VOC gases from the surrounding air (\(C_{air}\)-chamber concentration) and the spatial distribution of VOC concentration within the material. Typical layered building materials are in the form of composites such as wall-layering systems (paint/plasterboard/water vapour insulation) or floor-layering systems (wax/vinyl/adhesive/concrete).