Abstract
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.
Highlights
Volatile organic compounds (VOCs) are a diverse group of compounds that are present in elevated concentrations in indoor air, generally exceeding the outdoor levels by several times
A well-known example of biogenic VOCs (BVOCs) are volatile terpenes, secondary metabolites emitted from plants having a biological function as volatile signaling molecules, and are released from forests into the atmosphere in large quantities where they have an impact on climate (Laothawornkitkul et al 2009)
We have decided to use the latter term throughout this article and suggest its use when collectively referring to any VOC that has been emitted from either untreated or thermally modified softwood or hardwood, wood VOCs, such as formaldehyde or volatile terpenes, can be released from other sources like different materials or plants
Summary
Volatile organic compounds (VOCs) are a diverse group of compounds that are present in elevated concentrations in indoor air, generally exceeding the outdoor levels by several times. We have decided to use the latter term throughout this article and suggest its use when collectively referring to any VOC that has been emitted from either untreated or thermally modified softwood or hardwood, wood VOCs (sometimes abbreviated WVOCs), such as formaldehyde or volatile terpenes, can be released from other sources like different materials or plants. In this review article, we summarize the scientific literature on VOCs emitted from different species of untreated and thermally modified wood with the aim to give a general picture of the characteristics of softwood and hardwood emissions. The article may aid in the development of thermal modification techniques steered toward target wood VOCs
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