Characterizing source fingerprints and ageing processes in laboratory-generated secondary organic aerosols using proton-nuclear magnetic resonance (1H-NMR) analysis and HPLC HULIS determination

摘要

The study of secondary organic aerosol (SOA) in laboratory settings hasgreatly increased our knowledge of the diverse chemical processes andenvironmental conditions responsible for the formation of particulate matterstarting from biogenic and anthropogenic volatile compounds. However,characteristics of the different experimental setups and the way they impactthe composition and the timescale of formation of SOA are still subject todebate. In this study, SOA samples were generated using a potential aerosolmass (PAM) oxidation flow reactor using -pinene, naphthalene andisoprene as precursors. The PAM reactor facilitated exploration of SOAcomposition over atmospherically relevant photochemical ageing timescalesthat are unattainable in environmental chambers. The SOA samples wereanalyzed using two state-of-the-art analytical techniques for SOAcharacterization – proton nuclear magnetic resonance (H-NMR)spectroscopy and HPLC determination of humic-like substances (HULIS). Resultswere compared with previous Aerodyne aerosol mass spectrometer (AMS)measurements. The combined H-NMR, HPLC, and AMS datasets show that thecomposition of the studied SOA systems tend to converge to highly oxidizedorganic compounds upon prolonged OH exposures. Further, our H-NMRfindings show that only -pinene SOA acquires spectroscopic featurescomparable to those of ambient OA when exposed to at least1  ×  10 molec OH cm  ×  s OH exposure, ormultiple days of equivalent atmospheric OH oxidation. Over multiple days ofequivalent OH exposure, the formation of HULIS is observed in both -pinene SOA and in naphthalene SOA (maximum yields: 16 and 30 %,respectively, of total analyzed water-soluble organic carbon, WSOC), providing evidenceof the formation of humic-like polycarboxylic acids in unseeded SOA.