# Impact of Carpets on Indoor Air Quality
## 3 Effects of Carpets on IAQ
#### 3.1.3 VOC Transformation Reactions with Carpets  
As discussed in Section 3.1.1, there are primary emissions from various sources of indoor building materials present in the indoor air. Besides, a building material can release secondary emissions resulting from transformation reactions (like physical, biological, or chemical reactions) [64]. Materials with a large amount of organic compounds, such as carpets, wood, fabrics, and paint, can emit VOCs as secondary emissions [54]. In addition, newer carpets can have higher secondary emissions than older carpets [65]. One study showed that increasing ventilation might result in higher secondary emissions, especially for the material surface with high reactivity to oxidative degradation. Consequently, the secondary emissions, instead of the primary emissions, are expected to impact the perceived IAQ in the long run. It was observed that after a limited decay during the first one or two weeks, the odour intensity remained almost constant during the rest of the experiment period (50 days) [41]. One crucial transformation reaction in the carpet is the chemical reaction between oxidants and materials [64]. Ozone, as an oxidant agent, can react with gas-phase VOC emitted from building materials as well as the organic interface of building materials [40]. The ventilation rate and removal effects of surface interactions with building materials, such as wallpaper, latex paint, carpet, plywood, and plaster, can affect indoor ozone concentrations [66]. Among the building materials studied, carpets reacted significantly with ozone, owing to their high surface area and covering a large fraction of surfaces in the indoor area [14; 17]. Ozone reactions with carpet can lead to elevated concentrations of oxidized products (such as aliphatic aldehydes, i.e., formaldehyde, acetaldehyde, and aldehydes with 5-10 carbons), resulting in secondary emissions [66; 67]. Reactions among VOCs in an actual indoor environment are the source of short-lived, highly reactive compounds indoors, which makes the investigation of them by physical/chemical analyses difficult. The new reactive products may be readily sensed by occupants but are challenging to identify using standard analytical methods. While, it is possible to study the net effect of a complex VOCs mixture on human perception by sensory evaluation [68]. Therefore, sensory assessments are suitable for identifying variations derived from indoor chemistry, especially for variations missed by the routine analytical methods evaluating indoor air [69]. In this regard, sensory evaluations of ozone removal with building materials (plasterboard, carpet, linoleum, pinewood, and melamine) were conducted to reveal the perceptual effects. Results showed the greatest effect with significantly high odour intensity for carpet when exposed to ozone. Indeed, the compounds emissions from the carpet were transformed to oxidant compounds with negative odour notes caused by the ozone exposure [70]. Nylon carpets with SBR backing were exposed to an ozone environment to investigate the primary and secondary emissions [67]. The carpet backing primarily emitted styrene, 4-ethenylcyclohexene, and 4-PCH, while the nylon fibre emitted C5-C10 aldehydes \(\sim\)4 times more concentrated than the backing in the presence of ozone. Moreover, in the presence of ozone, benzaldehyde, benzoic acid, and acetophenone reached much higher concentrations in the chamber with the backing material than in the chamber containing the nylon fibres [67]. The research on six carpet fibre materials (Triexta, Poly-triexta, PP, Polyester, Nylon, and Wool) showed that carpets were virtuous sinks for ozone with the potential to diminish ozone levels indoors [54]. The ozone removal percentages and VOC emissions varied significantly as a function of fibre materials.