## 1 Introduction
The terpen emissions from conifer forests are widely discussed in the context of terpenes as a free radical source in the atmosphere [23; 24; 25], because hemi and monoterpenes are photochemically reactive compounds that affect ozone and carbon monoxide concentrations and their oxidation products can participate in the formation of secondary organic aerosol and cloud condensation nuclei [26]. When Norway spruces are attacked by bark beetles, the content of emitted terpenes from the stem significantly increases during the first two weeks of infestation. This growth is primarily attributed to the opening of constitutive resin storage and is quantified in the close vicinity of the stem. Different methods used for quantification have yielded a wide range of results, ranging from a 10 to 100-fold upturn [8; 27; 28]. The dominant compound in emissions was always \(\alpha\)-pinene, representing the time and spatial distribution of the other main monoterpenes [8]. The bouquet of infested trees also includes the aggregation pheromone produced by bark beetles. Beetles use this scent for navigation to aggregate, allowing them to overcome the tree's defense during the infestation [29]. The content of bark beetle pheromones is several orders of magnitude lower than that of \(\alpha\)-pinene in forests [30]. However, beetles are capable of discerning this signal from the background of host odors thanks to specialized receptors on their antennae, the organs responsible for perceiving smells [31]. Furthermore, beetles may orient themselves by detecting host compounds, primarily terpenes, when choosing a suitable host tree or habitat [32]. They also have specialized receptors for host compounds [33]. Numerous studies have investigated monoterpenes emitted by conifers in both laboratory and natural conditions. In the laboratory, collection systems can be readily optimized, as detailed in a comprehensive review [34]. In field conditions, VOC collection is more complex, and various techniques have been employed to address specific research questions [35]. The most common approach involves dynamic headspace sampling with compound collection onto sorbents, followed by extraction into solvents or thermal desorption. Additionally, solid-phase microextraction methods have been utilized (as shown in Table 1) [36; 37]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Tree Species/** & **Sampling** & **Compound (Unit)** & \begin{tabular}{c} **Technical Parameters** \\ **(Sorbent; Amount;** \\ **Flow Rate)** \\ \end{tabular}  & \ \begin{tabular}{c} **Time of** \\ **Sorption** \\ \end{tabular}  & \begin{tabular}{c} **Analytical** \\ **Method** \\ \end{tabular}  & **Source** \\ \hline \multirow{4}{*}{_Picea abies/_  
To study emissions on an ecosystem scale, researchers have employed various instrumental techniques, such as proton-transfer-reaction-time-of-flight (PTR-TOF) [46; 47; 48] mass spectrometry for quantifying monoterpene fluxes [19] or specialized gas chromatographs installed in situ at collection sites. However, these instruments can be expensive and lack portability, restricting data collection to a limited number of sites [49]. Hypothesis and objectives: This study is founded on a previously proposed concept suggesting that the number of volatile organic compounds emitted by trees, particularly monoterpenes, significantly increases within two weeks of bark beetle infestation [8]. This increase can serve as a measurable characteristic upon which the foundation of a newly developed alternative early bark beetle detection method may be based. Our objectives were to optimize the collection of \(\alpha\)-pinene emissions from spruce logs subjected to a controlled simulative bark beetle infestation in the laboratory and consequently detect the outdoor 3D dispersion of monoterpenes, represented by \(\alpha\)-pinene, in the surroundings of freshly infested spruce trees at horizontal and vertical distances.