# Impact of Carpets on Indoor Air Quality
## 1 Introduction  
Nowadays, people in the Western world spend most of their time (80-90%) indoors, where indoor air quality (IAQ) affects occupants' health and well-being [1]. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) defined IAQ as \"the types and concentrations of contaminants in indoor air that are known or suspected to affect people's comfort, well-being, health, learning outcomes, and work performance\" [2]. Two main classes of these contaminants consist of gaseous compounds (e.g., organic and inorganic gases) and particulate matters (both biological, including allergens, potential pathogens, and non-biological) [2]. Most of these compounds have a concentration consistently higher indoors than outdoors, affected by minimalization of ventilation (including infiltration) as a result of energy-saving measures [3]. Organic gases, comprising volatile organic compounds (VOCs, organic compounds with boiling points between 50 and 260 \({}^{\circ}\)C), very VOCs (VVOCs), and semi-VOCs (relatively low volatility VOCs), may cause several health problems, such as nose, eye, and throat irritation, loss of coordination, headaches, nausea, damage to the kidney, liver, and central nervous system, etc. [4]. Even though, most of the common VOCs in the buildings' indoor environment are considered nonreactive (NRVOCs), exposure to low concentrations of NRVOCs mixtures may cause human sensory irritation. Additionally, some VVOCs like formaldehyde show various health effects on humans, from irritation to sinonasal and nasopharyngeal cancer, even in low quantities [5]. Inorganic gases such as nitrogen oxides (NO\({}_{2}\)), carbon monoxide (CO), and carbon dioxide (CO\({}_{2}\)) are mainly produced by combustion, such as gas cooking and fossil fuel burning. The concentration of inorganic gases indoors depends on the unventedgas heaters and cookers, ventilation system, season, and outdoor levels [6]. Nowadays, the concentration is limited due to the application of electrical heating systems and application of mechanical ventilation. Another pollutant studied by many researchers is particulate matter (PM). PM refers to a broad class of chemical and physical substances that exist as liquid droplets or solid particles of various sizes [7] and is an important indicator of air pollution. Depending on their size, PM includes inhalable coarse particles (PM\({}_{10}\)) and fine particles (PM\({}_{2.5}\)) with particulate sizes below 10 \(\upmu\)m and 2.5 \(\upmu\)m, respectively. There is also a category of ultra-fine particles (PM\({}_{0.1}\)) with less than 0.1 \(\upmu\)m diameter, which a few researchers considered for studying carpets' behaviour. PM affects human health through respiratory symptoms, cardiovascular diseases, and lung cancer [8]. Generally, past epidemiological and toxicological research showed that smaller PMs have higher toxicity through mechanisms of oxidative stress and inflammation [9]. Remarkably, two major sources of organic compounds and PM can be found indoors, namely: people and their activities (such as heating, cooling, cooking, using printers, photocopiers, etc. ), and emissions from building materials [10]. The latter source of pollution is particularly interesting for its emission of organic compounds, while the first of both PM and VOCs. Building materials comprise finishing materials, such as paints and varnishes, treated and processed wood-based composite materials for furniture and finishes, and elements made of plastics and fibre textiles. The VOC concentrations emitted from building materials depend on the substance and the preparation of the building materials, the time elapsed from installation/use (for example, in the case of carpet, VOC emissions are in general the highest when applied and decrease over time) [11; 12; 13]. PM concentrations depend on the activities performed indoors, the exchange with outdoor air, and the (re)suspension of particles from indoor surfaces, such as flooring materials.