## 1 Introduction
### Bottom-Up Lithosphere-Atmosphere-Ionosphere Coupling Interaction Mechanisms  
The existence of bottom-up lithosphere-atmosphere-ionosphere effects before volcano eruptions and earthquakes is a controversial scientific topic. For example, a recent paper by [PERSON] et al. proposed that what was considered a cause-effect interaction between radon emission and electromagnetic anomalies before Mw9.1 Tohoku (offshore of Oshika Peninsula, Japan) 2011 earthquake are two independent phenomena; nevertheless, the authors still support them as separate precursors of the mega-thrust earthquake [28]. In this paper, we investigated a volcano and not an earthquake. Literature on LAIC and volcano is less rich than on LAIC and earthquakes, but the volcanos are more known for their geological features and underground structures. It is important to point out that the researchers proposed several different models to explain the possible interactions between lithosphere-atmosphere-ionosphere [29], which we will briefly illustrate in the following. The differences in the proposed models are based on the mechanism that could be an electromagnetic interaction based on Maxwell equations or a mix of mechanic, thermal, chemical, and electromagnetic phenomena. Such ways of interaction affect the parameters differently with specific propagation times; for example, an electromagnetic wave propagates at the speed of light in the medium that permits it to cover 500 km in 1.7 ms (in the air). In comparison, an acoustic wave at the speed of sound requires about 25 min to cover 500 km (in the air in standard conditions). The basic source under the volcano is the magma accumulation in its magmatic chambers, and several volcanos have more than one (for example, Changbaishan in China [30] or La Palma object of this study [31]). The accumulation and uplift of the magma prior to the eruption can bring at least three effects: firstly, an increase in the temperature of the lithosphere under the volcano, secondly a demagnetization of the crustal due to the increase of the temperature above the Curie temperature, and thirdly a direct degassing from the cone of the volcano due to the rise of underground pressure [32]. The increase in temperature in the underwater lithosphere can trigger an increase in the growth rate of algae that are directly responsible for DyMethil Sulphide (CH\({}_{3}\)SCH\({}_{3}\) or DMS) emission in the atmosphere [33]. Furthermore, DMS can be oxidated in the air, forming sulphur dioxide [34]. Despite the presence in the atmosphere of SO\({}_{2}\) as a result of oxidation of DMS, we can expect a direct emission from the volcano, as it is among the primary sources of SO\({}_{2}\) in the atmosphere [35]. SO\({}_{2}\) can be oxidised, producing sulphate aerosol, so the whole chemical chain is: DMS oxidised in SO\({}_{2}\), which is oxidised in aerosol [36]. Carbon monoxide is also directly emitted by volcanoes, even if its amount compared to other natural sources, like the burning of vegetation and even anthropogenic sources, is negligible for the global budget [37]. Volcanoes also emit water vapour (H\({}_{2}\)O), CO\({}_{2}\), H\({}_{2}\)S, HCl, hydrogen fluoride, hydrogen bromide, CH\({}_{4}\), CH\({}_{3}\)Cl, H\({}_{2}\), and heavy metals, as explained by [PERSON] and [PERSON] [36], but these other substances are not considered in this study. The process of accumulation of gases in the atmosphere could bring ionization of the air, which is an important key driver of possible electrical phenomena in the atmosphere and ionosphere, altering the global electric circuit of Earth [2; 38]. The chain of these phenomena has been graphically resumed in Figure 2A. Another important factor to take into account is the required time of such phenomena, which could be days or weeks, according to some previous studies on earthquakes (e.g., [39; 40]). Additionally, the persistence in the atmosphere of the investigated chemical compounds needs to be taken into account--it is 0.7 days for DMS, some days for SO\({}_{2}\), and about two months for CO [36].