Characterization of crucial fragments during the nucleation and growth of secondary organic aerosol from the high-NO photo-oxidation of α-pinene

We propose the use of thermal-desorption dichloromethane-induced low-pressure photoionization mass spectrometry (TD-CH2Cl2-induced LPPI-MS) via a laboratory-built krypton vacuum ultraviolet lamp for the real-time analysis of alpha-pinene secondary organic aerosol (alpha P-SOA). Using this technology, the peak intensities of the majority of SOA were enhanced by at least two orders of magnitude after doping with 720 ppm dichloromethane. Clear temporal evolutions of the SOA oxidation products with particle formation were also observed. The molecular ion peaks at m/z value of 153 and 109 showed a similar sharp increase with particle-number concentration. These two species (i.e. protonated alpha-campholenic aldehyde or dehydrated protonated pinalic-3-acid) with the fragment at m/z 153 and 109 may be critical species to prompt new particle formation. Furthermore, the monomers with the fragment ion peaks at m/z value of 69 and 87 (i.e. protonated pinonic acid, pinic acid, oxopinonic acid, and OH-pinonic acid etc.) were found to be intermediate species with high reactivities during SOA growth. The obtained results provide supplementary knowledge regarding the characterization and temporal evolution of the key components that promote alpha P-SOA formation.