## 3 Results and Discussion
### Quantitative VOC Differences between the Bio-Based Boards
In addition, both total and individual VOCs rate changes depending on varying hot-pressing temperature [32] and indoor air temperature [33] were reported and comply with the results of our study. It is clear that different kinds of overlaying or coating should be applied to find out the best reducing effect of total VOCs, particularly furfural. For example, overlaying by a phenolic paper of MDF reduced formaldehyde and total VOC emissions by 99% and 88%, respectively, while epoxy powder coatings of the same fiberboard resulted in a similar effect on the reduction of formaldehyde and even better reduction (94%) of VOCs [34]. Sodium metabisulphite was demonstrated as an excellent aldehyde scavenger capable of substantially reducing total VOCs in particleboards with different lignocellulosicas [28]. Acetic acid was substantially reduced in parquet products by a solvent-based coating system (PU-1) [5]. The VOCs from the GA- and B-based wood boards had a smaller number of individual components, and the total peak areas of VOCs were lower (Figure 4C), than in the case of hemp and wheat. On the one hand, the lower total VOCs from woody materials could be associated with their earlier production time. However, on the other hand, the VOC emissions were more caused by the freshly cut surfaces before HS-SPME. It was reported that the amount of VOCs highly depends on the manufacturing process of wood-based composite. For example, a lower SE treatment severity of softwood bark resulted in higher VOC levels from produced pellets [19]. It was also reported that total VOCs from MDF were highly influenced by pressing temperature, followed by pressing time [35]. Figure 4 shows that the VOC area units from all four biomass species were almost the same after the 28 days: 36 for HS 800-6, 26 for WS 800-6, 28 for GA 700, and 25 for B 700, indicating a certain equilibrium of persistent VOCs emitted from binder-less boards, unlike the adhesive-bonded ones (SA-PB and commercial-PB). As a comparison, the total VOCs from the commercial-PB were up to 26 AU, which decreased to ~15 AU after 28 days and equaled the SA-PB total VOCs concentration (Figure 4D). Regarding VOC emission changes over time, the overall trend was a significant decrease in the total VOCs by 52-77% in practically all binder-less board samples after 28 days. Likewise, the number of detected peaks decreased by 23-58%, as the concentration of the minor components dropped below the detection limit. This shows that passive airing during storage removed a large part of the VOCs, which arose from the freshly cut surfaces of the material. A similar tendency was also approved for the pellets from SE softwood bark in enclosed storage, demonstrating a substantial decrease in VOCs after 6 days [18]. Figure 5: Derived thermogravimetry of steam-exploded (220 \({}^{\circ}\)C/2 min) HS and WS samples. The suberinic acid-bonded particleboard did not show a significant decrease in VOCs over time, which were initially low. Namely, the VOCs of the SA-PB sample were comparable to the commercial sample (Figure 4D). Finally, it is worth noting that after 28 days, the overlayed HS-based board released an amount of VOCs comparable to SA-PB and commercial samples with almost no furfural, which is the best result among all binder-less boards investigated during this study.