Investigation of the Physical Properties of Eucalyptus and Pinus halepensis Essential Oils Using Dielectric Spectroscopy and Gas Chromatography–Mass Spectrometry

The gas chromatography-mass spectrometry and dielectric spectroscopy techniques are used to characterize the thermodynamic properties of the essential oils extracted from two main Mediterranean wildland fuels, namely eucalyptus leaves and Pinus halepensis needles. These oils are assumed to be representative of the fuels organic volatile components that exhibit different fire behaviors. The relaxation frequencies determined from the peak of the imaginary permittivity spectra using the Havriliak–Negami empirical law revealed the Arrhenius dependence on temperature. Two activation energies are obtained: the first is around 4.13 kJ/mol for both species, and the second activation energy is around 1.27 kJ/mol for the Pinus halepensis essential oil and around 2.15 kJ/mol for the eucalyptus essential oil. Qualitative and quantitative composition differences are observed with GC–MS measurements for eucalyptus leaves and Pinus halepensis needles essential oils.