Fig. 7

The relationship between the number of rings of the PAHs and their relative abundance normalized to benzene at 100. The abundance profiles were from benzene (monocyclic), naphthalene (bicyclic), phenanthrene (tricyclic), and pyrene (tetracyclic), where the concentrations of alkyl-PAHs were not included in the determination of each relative abundance. For further description of carbonaceous products, the detailed analysis of soluble organic matter using polar and apolar solvents will have to be performed by high-resolution mass spectrometry with appropriate wet-chemical treatments (e.g., Orbitrap mass spectrometry by Oba et al. 2019; Isotope ratio mass spectrometry by Takano et al. 2015)