# Impact of Carpets on Indoor Air Quality
## 3 Effects of Carpets on IAQ
#### 3.1.1. Emission of VOCs with Carpets  
This section discusses the source, kind of VOCs, and emission mechanism, as well as relevant parameters affecting the emission rate from carpets. Carpets can emit VOCs, SVOCs, and microbial VOCs (MVOCs). The most emitted pollutants by carpets are VOCs such as 4-phenylcyclohexene (4-PCH, the source of new carpet odour), aromatic compounds (benzene, styrene, toluene, xylenes), and carbonyl compounds. This emission can range from 10 to 10,000 \(\mathrm{\SIUnitSymbolMicro m^{-2}}\) h\({}^{-1}\)[4; 28]. Additionally, some SVOCs emitted by carpets are treated by finishing agents, such as per- and polyfluoroalkyl substances (PFAS) from soil retardants [29], organohalogen and organophosphorus from flame retardants [18], triclosan from antimicrobials [30], phthalate esters (PAEs) in plasticizer PVC backing [22; 31], p-dichlorobenzene from moth repellent, tetrachloroethene from dry-cleaning agents [32], and silicon composition from water repellent [33]. Figure 3: Impact of the carpets on the VOCs concentration in indoor air. Figure 2: The structure of carpets and categorization of the natural and synthetic fibre carpets. Moreover, microorganisms can emit MVOCs (especially 1-octen-3-ol and 2-ethyl-1-hexanol) as part of the metabolic processes of microbes. The emission of MVOCs depends on the water content of the carpet, the availability of nutrients, and the presence of oxygen [34]. However, more research is required to better understand when microbial growth occurs and MVOCs are emitted from humid carpets. There are various measurement methodologies for studying the impact of carpets on IAQ. Practically, the ISO 16,000 series and EN 16,516 are used for sampling, preparation, and measuring the emission of VOCs [35; 36]. Nowadays, some voluntary standards are involved in measuring the VOCs emitted by carpets to label carpets with low emission rates. The most applied ones are green labels supported by the Carpet and Rug Institute, the trade association for the North American carpet industry, and Gemeinschaft umwellfreundlicher Teppichboden (GUT), supported by the European textile floor-covering industry. To receive GUT Certification, the emission rates for several VOCs must be less than certain defined rates: the VOCs and SVOCs emissions must be less than 250 \(\upmu\)g m\({}^{-3}\) and 30 \(\upmu\)g m\({}^{-3}\), respectively, after three days [37]. Most of these labelling systems use chemical analyses for the measurement of TVOCs, and some specific VOCs and a few, like GUT, use odour tests with trained panels [38; 39]. The emission of VOCs from carpets can be categorized as primary and secondary emissions based on the bounding to the carpet. The primary emissions refer to non-bound, or free VOCs of the carpet, such as low molecular weight VOCs used as additives, solvents, and unreacted raw materials like monomers. The secondary emission group comprises emissions of originally physically or chemically bound VOCs of carpet materials. These VOCs are emitted from the carpet by various mechanisms, such as oxidation, decomposition, sorption processes, polymer degradation, maintenance, and microbiological emission (Section 3.1.3). In some cases, describing VOC transfer is complicated due to the impossibility of separating the free VOC from the physically adsorbed VOCs. Significantly, VOCs move freely from adsorbed phase to the gas phase or vice versa to satisfy surface equilibrium due to weak bounding (van der Waal's force) between VOCs and pore surfaces [40]. The primary emissions decrease moderately fast (usually within a year). In contrast, secondary emissions for some building product types, e.g., linoleum, may remain for the entire life of the building product [41]. Two mechanisms reflect the emission rate of VOCs from building materials with no internal chemical reactions: (1) the diffusion of VOCs within the building materials and (2) the evaporation from the building materials' surface to the ambient air.