# The Ability to Control VOC Emissions from Multilayer Building Materials
## 1 Introduction
### State of Knowledge-Emission Modelling  
In order to make basic assumptions about the shape of the VOC emission model and its components for heated floors (considering a higher temperature and humidity), it is necessary to present the existing state of the art on emission modelling. Based on a provided review in this section, the authors in the next section, Methods, propose a model that is used later to determine the VOC concentration regression profiles based on the experimental results (VOC emission test in chambers). The prediction of VOC concentration in a chamber or room is attempted by modelling carried out on the basis of the analysis of the influence of variables, e.g., temperature, air humidity and air change rate on the characteristic parameters of the physical processes of emission: initial VOC concentration in solid material (\(\mu\)g m\({}^{-3}\)), diffusion factor of a given VOC in the emitting building material \(D_{m}\) (m\({}^{2}\)/s) and the dimensionless mass partition coefficients \(K_{ma}\) of the diffusing agent into the part of the mass remaining in the porous material and the part of the mass released into the environment above the emitting surface. These parameters are the output of models of convergence of heat diffusion and the VOC migration processes in porous materials (single and multilayer, dry and wet environments). Existing emission models typically fall into one of the following types: empirical, analytical or mass-transfer-equation-based. The literature analysis suggests the need to refine this division of models considering verified assessments of their reliability, the possibility of generalisation and the ease of use in practice, leading to the presentation of their classification proposals (see Figure A1, Appendix A). The first group of publications contains five basic publications on emission models based on the theory of mass transfer of VOC compounds from building materials, in which models of the first researchers of emission phenomena from a single homogeneous layer and a double layer are presented. [PERSON] et al. [10] first presented an emission analysis with a model to predict diffusion-controlled VOC emissions from homogeneous building materials. Although the model is useful and straightforward in many cases, an extension of the assumption neglecting convective mass transfer resistance through the air boundary layer was not justified under all conditions. This model's parameters were the initial VOC concentrations in the material, the material-air partition coefficient and the material's VOC diffusion coefficient. The presented model has been verified by comparing it with the carpet emission tests results and analysing the determined model parameters' influence on the emission profile runs. [PERSON] et al. [11] used this analytical model to calculate the emission rate of vinyl flooring and found a relatively good agreement. Based on the model of [PERSON] et al. [10], [PERSON] et al. [12] developed an analytical model to study the transition state and reproduce the reversible effect of secondary adsorption as a response to the simultaneous emissions of pollutants. [PERSON] and [PERSON] [13] developed a numerical model taking into account the mass transfer resistance by introducing mass transfer coefficients; however, they assumed that the VOC concentration in the air should be zero in the gas phase. [PERSON] and [PERSON] [14] presented an improved model that overcame the two previous models' limitations and obtained an analytical solution. However, as the authors' reserve, [PERSON] and [PERSON]'s solution is not fully analytical because it is coupled with the air concentration and needs to be solved simultaneously. Later, [PERSON] and [PERSON] [15] developed a fully analytical solution of the given system of [PERSON] and [PERSON]'s equations [14]. The [PERSON] model was later the most frequently cited and left the largest trace in the existing models of physical VOC emission processes from building materials.