## 2 Results and Discussion
### Application to Real Samples  
Both of the optimized and validated analytical methodologies were subsequently applied in the analysis of BVOCs released by the leaves from the _E. globulus_ Labill. and _P. pinaster_ Aiton species, sampled in 'Parques de Sintra' during June 2020 and September 2021. The main goal of this survey was to evaluate the average number of the major monoterpenoids emitted from the leaves and, therefore, anticipate the influence that they may have in the natural forest environment, particularly under the occurrence of forest fires. Assays performed on the BVOCs release from the leaves of the tree species showed, as expected, identical pattern profiling through both methodologies, demonstrating similar analytical responses, as stated before. Figure 6 exemplifies the total ion chromatograms obtained from in vitro assays on the leaves of _E. globulus_ Labill. and _P. pinaster_ Aiton by the HS-SPME(PDMS/DVB)/GC-MS (a,b) and HS-BA\(\mu\)E(R)/GC-MS (c,d) methodologies, respectively, in which identical profiles are achieved, as well as remarkable selectivity and sensitivity. During the aforementioned sampling period, the average levels obtained from assays on the major BVOCs released by the leaf samples indicated that _P. pinaster_ Aiton presented very significant emissions of \(\beta\)-pinene (\(3503.8\pm 396.3\)-\(159.4\pm 19.1\)\(\mu\)g g\({}^{-1}\)), \(\alpha\) -pinene (\(1281.6\pm 168.5\)-\(105.7\pm 1.6\)\(\mu\)g g\({}^{-1}\)), limonene (\(731.9\pm 115.3\)-\(9.2\pm 1.4\)\(\mu\)g g\({}^{-1}\)) and myrcene (\(397.7\pm 28.9\)-\(10.3\pm 0.8\)\(\mu\)g g\({}^{-1}\)). For the leaf samples from _E. globulus_ Labill., considerable emissions of the major BVOCs were also observed (\(95.2\pm 15.6\)\(\mu\)g g\({}^{-1}\) \(<\)\(\alpha\)-pinene \(<\)\(3183.3\pm 353.6\)\(\mu\)g g\({}^{-1}\); \(39.6\pm 1.5\)\(\mu\)g g\({}^{-1}\)\(<\) limonene \(<\)\(883.0\pm 18.4\)\(\mu\)g g\({}^{-1}\); \(18.4\pm 1.2\)\(\mu\)g g\({}^{-1}\)\(<\) myrcene \(<\)\(131.6\pm 14.1\)\(\mu\)g g\({}^{-1}\), \(10.2\pm 1.3\)\(\mu\)g g\({}^{-1}\)\(<\)\(\beta\)-pinene \(<\)\(78.2\)\(\pm\)\(11.8\)\(\mu\)g g\({}^{-1}\)), and, as expected, 1,8-cineole was only detected in this species in very significant amounts (\(7828.0\pm 40.0\)-\(670.7\pm 110.8\)\(\mu\)g g\({}^{-1}\)). Nevertheless, the maximum contents detected for \(\alpha\)-pinene, \(\beta\)-pinene and myrcene were lower compared with those reported by [PERSON] et al. (2015), who reported amounts of \(4357.5\), \(6187.2\) and \(1377.8\)\(\mu\)g g\({}^{-1}\), respectively, from the _P. pinaster_ Aiton species by using a conventional analytical approach, constituted by ultrasonic extraction with organic solvents prior to GC-MS analysis. The contents detected in the present study for limonene were relatively higher than the reported value (\(463.2\)\(\mu\)g g\({}^{-1}\)). Furthermore, the concentrations variability on the major BVOCs of the same tree species is probably associated with the different chemotypes, which could affect the pattern of compounds released ([PERSON] et al., 2016). From the data achieved, we can state that there was a clear variation in the BVOCs emission over the period of time in which the leaf sampling took place, although it was not possible to quite understand the pattern that could explain the reason for such variability, whether from biological, atmospheric (temperature, moisture, wind, etc.) or anthropogenic constraints that can promote stressful conditions for the tree species or any other reason. However, the number of volatiles emitted by the sampled leaves is very significant and, therefore, may contribute to the accumulation of BVOCs in the natural forest environment, under certain atmospheric conditions. In general, at \(30\)\({}^{\circ}\)C, the maximum concentrations emitted from these BVOCs by the crowns of the tree species under study (\(0.01\)-\(1.26\)\(\mu\)g m\({}^{-3}\)) are far below their lower flammability limits (LFL), which, for 1,8-cineole, is between \(38.2\) and \(38.8\)\(\mu\)m\({}^{-3}\).