## 3 Discussion
Indeed, in the first and second sampling point, the total amount of MTs obtained using DBSS was double that of the static technique (Figure 5). The differences in the amount of BVOCs collected between the two techniques were particularly noticeable at sampling point 3 (Figure 5), in which qualitative differences were also observed (Figure 4). These qualitative differences observed at sampling point 3 may be explained by considering the lower air temperature recorded in October compared to June. Indeed, since BVOC emission is temperature-dependent, with an optimum around 25 \({}^{\circ}\)C, the collection of BVOCs using DBSS resulted particularly efficient when environmental conditions limited their emission [3, 58]. Furthermore, a potential sink effect played by humidity, reducing BVOC adsorption in SPME fibers, could exacerbate this outcome since these compounds are water soluble at low concentrations [59]. Therefore, the collection of BVOCs without the fan-sampler system may reduce the BVOC adsorption on SPME fibers when present in traces or under windy weather conditions [60, 61]. The observed variations in the scale of the total monoterenes obtained between sampling point 1 and sampling points 2 and 3 (Figure 5) could be explained by the differences in plant characteristics and site conditions. Indeed, in sampling point 1, the studied plants were represented by 15 three-year-old \(Q\). _ilex_ potted plants, while in sampling points 2 and 3, BVOCs were collected in a natural forest with mature trees. Therefore, the dimensions of the canopy were very different, as well as the environmental conditions of the sampling. In addition, the potted \(Q\). _ilex_ plants, with a mean height of 1.2 m, were positioned at the center of an open field subjected to wind gusts that could have reduced the deposition of BVOCs into the fibers compared to the under-canopy conditions of the forest. Finally, the site of sampling point 1 was located in Sesto Fiorentino, a semi-urban area in which BVOC degradation by atmospheric oxidants could have been occurred [62]. In particular, since the sampling was conducted during the central hours of the day, eventual monoterene oxidation would have been caused by the presence of hydroxy radicals (OH) [63]. However, these types of degradation products were not detected in our experiment. It is important to mention that the range of total MTs obtained in sampling points 2-3, which were carried out in the same sampling area but in different seasons, provided similar results when employing the DBSS strategy. This finding shows the high potential and good repeatability of the DBSS strategy. Another advantage of the DBSS could derive from the homogenization of the sample through the fan. The creation of turbulent airflow, obtained by combining the fan and the net in front of the SPME fiber. BVOCs under forest canopy can have heterogeneous concentrations [39], and the emissions are influenced by several factors: different seasons, meteorological conditions, sunlight exposure, altitude, tree species and damages from herbivores [3, 8, 64]. Altogether, our results demonstrated the potential and versatility of the DBSS for the rapid in situ measurement of BVOCs under different environmental conditions. In particular, the DBSS allowed identifying the typical compounds emitted by \(Q\). _ilex_. Indeed, qualitative MTs identification carried out in our study is consistent with results reported in previous experiments conducted on the same species both in pots and in field conditions [49; 50; 65; 66]. In all sampling points, \(\alpha\)-pinene, \(\alpha\)-thujene, \(\beta\)-pinene, sabinene and d-limonene were the most abundant compounds emitted by _Q. ilex_[5; 46; 48], which represented about 65-80% of the total detected monoterpenes. While other BVOCs such as car-3-ene, \(p\)-cymene and 1,8-cineole were also detected in lower amounts [46; 48; 67]. In addition, in agreement with [PERSON] [47], our system was able to collect \(\beta\)-phellandrene, \(\alpha\)-terpinene, \(\gamma\)-terpinene and terpinolene.