Integration with the mass spectra was performed between the column's dead time (2 min) and the start of the column re-equilibration time (16 min). Decon2LS program (spec.github.io) was used to cluster all mass spectra from each temperature (room temperature, heated to 36 °C, and heated to 52 °C). Background peaks only present in the blank samples were removed from all SOA spectra. Peaks containing C isotopes were removed. Mass accuracy of ± 0.0005 m/z units was used to assign peaks with formulae CxHyOz with restrictions implemented for atomic ratios: C < 40, H < 80, and O < 35. The assigned formulas were corrected for deprotonation in the negative ionization mode and reported as neutral formulae of catechol SOA.