Fig. 3.
Representative (1) extracted ion chromatograms, (2) MS spectra, and (3) MS/MS spectra, measured by UPLC/(−)ESI-Q-TOF-MS, of dimer esters in SOA produced from the O3-initiated oxidation of β-pinene (Table 1, type 1) presumed to form from (A) cis-pinic acid (C9H14O4), (B) cis-norpinic acid (C8H12O4), and (C) diaterpenylic acid (C8H14O5). MS/MS peaks are colored to denote O3-derived (red) and OH-derived (blue) fragment ions. Numbers in MS/MS spectra correspond to nominal m/z values of [M−H]− fragment ions; ionic formulas [CxHyOz]− are given in parentheses. *Indicates peaks that underwent a one-unit mass shift on formation from 13C-β-pinene.