Volatile organic compounds emitted from untreated and thermally modified wood - a review

Volatile organic compounds (VOCs) are a diverse group of compounds that can have a strong impact on indoor air quality.Wood and thermally modified wood emit VOCs, which are referred to as wood VOCs, and can elicit various negative or positive effects in different organisms, including humans. Wood is a complex multicomponent biopolymer with inherent variability, which is also reflected in the emissions of VOCs. Variability in wood VOC emissions has been attributed to endogenous and exogenous factors, such as wood species, type of wood sample, wood treatment, etc. Nevertheless, studies have reported reasonably consistent results regarding VOC emissions from individual (thermally modified) wood species. Softwoods emit the highest concentrations of wood VOCs composed primarily of volatile terpene emissions (70-90%) and lower concentrations of hexanal and acetic acid (10-25%). VOC emissions from hardwoods are considerably lower (approximately 50 times) and include hexanal and pentanal, acetic acid, as well as other VOCs formed during wood degradation processes, but not volatile terpenes. Total VOC emissions from softwoods are reduced following thermal treatment, whereas emissions are increased from hardwoods after thermal treatment. In thermally treated softwoods, emissions of volatile terpenes and hexanal are drastically decreased, whereas those of acetic acid and furfural increase. Similarly, in thermally treated hardwoods, the emissions of hexanal and pentanal are reduced, whereas acetic acid and furfural, as well as other compounds increase. In addition, formaldehyde emissions are ubiquitous, albeit at low concentrations, but increase following heat treatment. Furthermore, the number of VOCs emitted from thermally treated wood increases with heat treatment temperature. This review article will help guide future research, particularly the evaluation of the impact of different wood species on indoor air quality and the development ofmodification techniques that target extraction or suppression of VOCemissions.