Exploring biogenic secondary organic aerosol using a PTRMS-CHARON in laboratory experiments: characterization and fingerprint analysis

Abstract

Volatile Organic Compounds (VOC), particularly of biogenic origin emitted by vegetation and soils, play an important role in the global Organic Aerosol (OA) budget. The introduction of field-deployable Aerosol Mass Spectrometers in the early 2000s, combined with statistical analysis of their mass spectra, has significantly improved our understanding of the impact of secondary processes on fine-mode aerosol concentrations. While delivering innovative and significant insights, those analyses usually fail to explicitly identify precursors/mechanisms. In this context, this work focuses on laboratory-generated secondary OA (SOA) of biogenic VOC and its spectral analysis through a new generation of aerosol mass spectrometers, notably a Proton Transfer Reaction Mass Spectrometer coupled to a CHemical Analysis of aeRosol ONline (PTRMS-CHARON) inlet. Aerosol particles were formed in the new DouAir atmospheric chamber via isoprene (ISOP) OH oxidation, monoterpene O3 (limonene, MT), and sesquiterpene O3 (β-caryophyllene, SQT) oxidation. ISOP experiments targeted “low-NO” environments, typically remote forested tropical areas, via epoxidiols formation (ISOP-IEPOX-SOA), or through an alternative branching favored in the absence of acidic seed particles (ISOP-non-IEPOX-SOA) and “high NO” environments, representative in urban and polluted regions (ISOP-NO-SOA). Experiments showed that those five SOA formation pathways (ISOP-IEPOX-SOA, ISOP-non-IEPOX-SOA, ISOP-NO-SOA, and the ozonolysis reactions of MT and SQT) exhibited distinguishable spectra, with identifiable tracer ions, such as m/z 119.07 (C5H10O3), m/z 137.081 (C5H12O4) for ISOP-IEPOX-SOA, C5H10O4 (m/z 135.070), C5H10O6 (m/z 167.055) for ISOP-non-IEPOX-SOA, and m/z 85.028 (C4H4O2) for NO-SOA pathways, as well as molecules with C7-C10 and C7-C15 structures, including characteristic fragments, identified during MT and SQT oxidation experiments, respectively. Notably, m/z 83.049 (C5H6O) was detected in both low-NO isoprene pathways, suggesting a broader diagnostic role. These laboratory findings depict promising results for ambient near-real-time biogenic SOA source apportionment, notably in forested and/or urbanized areas.