Polycyclic Aromatic Hydrocarbons (PAHs) in Ambient Aerosols from Beijing: Characterization of Low Volatile PAHs by Positive-Ion Atmospheric Pressure Photoionization (APPI) Coupled with Fourier Transform Ion Cyclotron Resonance

Aromatic fractions derived from aerosol samples were characterized by gas chromatography and mass spectrometry (GC-MS), high temperature simulated distillation (SIMDIS), and positive-ion atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), respectively. It was found that about 27 wt % compounds in aromatic fractions could not be eluted from a GC column and some large molecule PAHs were neglected in GC-MS analysis. APPI FT-ICR MS was proven to be a powerful approach for characterizing the molecular composition of aromatics, especially for the large molecular species. An aromatic sample from Beijing urban aerosol was successfully characterized by APPI FT-ICR MS. Results showed that most abundant aromatic compounds in PM2.5 (particles with aerodynamic diameter ≤2.5 μm) were highly condensed hydrocarbons with 4–8 aromatic rings and their homologues with very short alkyl chains. Furthermore, heteroatom-containing hydrocarbons were found as the significant components of the aromatic fractions: O1, O2, N1, and S1 class species with 10–28 DBEs (double bond equivalents) and 14–38 carbon numbers were identified by APPI FT-ICR MS. The heteroatom PAHs had similar DBEs and carbon number distribution as regular PAHs.