## 2 Volatiles in Heritage Environments
### Volatiles Emitted from Heritage Objects
Other paper components such as binders, glues, printing inks, resin residues and waxy compounds degrade as well, producing compounds such as alcohols, aldehydes, ketones, carboxylic acids and hydrocarbons. The investigation of VOC emissions contributes to the determination of material properties. The production of volatile degradation products can be quantitatively correlated with paper properties, such as rosin, lignin, degree of polymerization of cellulose, carbonyl group content and acidity of the paper [14]. In addition, some of the emitted volatiles have a distinct odour, making it possible to identify old books by smell alone. The most commonly detected by smell are benzaldehyde, ethylbenzene, furfural, toluene, 2-ethylhexanol with a sweetish, almond-like and floral odour [11; 25], vanillin with a vanilla-like odour [14] and guaiacol, which is produced during lignin degradation, with a typical smokoy odour [25]. **Plastic** objects are found as works of art in many modern art collections, and the most commonly investigated objects are made of cellulose nitrate, cellulose acetate and poly(vinyl chloride) [27; 28]. Objects made of cellulose nitrate produce NO\({}_{2}\) as a degradation product, and volatile emissions include those from plasticizers used in the production of plastics. In cellulose nitrate artifacts, we can detect camphor, which was traditionally used as a plasticizer, and in some objects also diethyl phthalate [27; 28; 29]. In addition, the emission of furfural, which is formed during the acid-catalysed hydrolysis of cellulose, and camphor derivatives--camphene and campholenal--has also been detected [27; 28]. Cellulose nitrate releases NO\({}_{2}\), and although it is not a VOC, it is important as it can corrode metals upon reaction with atmospheric moisture, and the conversion to nitrous acid and nitric acid catalyses the hydrolysis of glycosidic bonds in cellulose, degrading paper and wood [29]. Cellulose acetate objects mainly release acetic acid. This common degradation phenomenon is called \"vinegar syndrome\" due to the strong odour of acetic acid [27; 28]. Cellulose acetate is mainly degraded by hydrolysis, in which the acetate groups on the glucose ring are replaced by hydroxyl groups and acetic acid is released. Therefore, acetic acid can be regarded as a specific marker for the degradation of cellulose acetate [27]. Two common plasticizers are dimethyl and diethyl phthalate, as well as the antioxidant butylated hydroxytoluene in smaller amounts. Accelerated degradation studies of cellulose acetate have detected toluene and phenol. In this context, phenol is an indicator for the degradation of the plasticizer triphenyl phosphate (TPP) [10; 27]. A significant proportion of modern art objects in museums is made of PVC, whose main degradation product is HCl, which can accelerate degradation, causing discoloration and decomposition of other objects [27; 30]. In PVC samples, the loss of plasticizers is reflected in the formation of bis(2-ethylhexyl)phthalate and its degradation product 2-ethylhexanol [28]. Various volatiles emitted by PVC have been identified, including hydrocarbons from pentane to octadecane, butoxyethanol, cyclohexanone, 2-ethoxyhexanol, 2-ethylhexanol, 2-ethylhexanoic acid, tri-methylbenzene, phenol, diethylbenzene and toluene. These are mainly \"non-specific\" VOCs, and it is not possible to define a specific marker. Museum objects made of PVC mainly decompose with the formation of HCl as a degradation product, which can accelerate degradation of exhibited objects, such as ceramics and metals [30; 31]. The study by [PERSON] et al. [29] shows the cross-infection effect between cellulose and diverse plastics. In the case of cellulose acetate, large amounts of acetic acid are emitted, which catalyses the hydrolysis of the glycosidic bonds of cellulose and accelerates the degradation of cellulose. When this emission occurs at room temperature, it has been shown to decompose other items made of organic materials, metals or other plastics.