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

Abstract

Abstract. The study of secondary organic aerosol (SOA) in laboratory settings has greatly increased our knowledge of the diverse chemical processes and environmental conditions responsible for the formation of particulate matter starting from biogenic and anthropogenic volatile compounds. However, characteristics of the different experimental setups and the way they impact the composition and the timescale of formation of SOA are still subject to debate. In this study, SOA samples were generated using a potential aerosol mass (PAM) oxidation flow reactor using α-pinene, naphthalene and isoprene as precursors. The PAM reactor facilitated exploration of SOA composition over atmospherically relevant photochemical ageing timescales that are unattainable in environmental chambers. The SOA samples were analyzed using two state-of-the-art analytical techniques for SOA characterization -proton nuclear magnetic resonance ( 1 H-NMR) spectroscopy and HPLC determination of humiclike substances (HULIS). Results were compared with previous Aerodyne aerosol mass spectrometer (AMS) measurements. The combined 1 H-NMR, HPLC, and AMS datasets show that the composition of the studied SOA systems tend to converge to highly oxidized organic compounds upon prolonged OH exposures. Further, our 1 H-NMR findings show that only α-pinene SOA acquires spectroscopic features comparable to those of ambient OA when exposed to at least 1 × 10 12 molec OH cm −3 × s OH exposure, or multiple days of equivalent atmospheric OH oxidation. Over multiple days of equivalent OH exposure, the formation of HULIS is observed in both α-pinene SOA and in naphthalene SOA (maximum yields: 16 and 30 %, respectively, of total analyzed water-soluble organic carbon, WSOC), providing evidence of the formation of humic-like polycarboxylic acids in unseeded SOA.

Measurement report: Particle-size-dependent fluorescence properties of water-soluble organic compounds (WSOCs) and their atmospheric implications for the aging of WSOCs

“…The specific fluorescence area was widened in the ambient sample and, thus, had a higher AFI/WSOC ratio when WSOC concentrations were at a comparable level. The continuous oxidation of organics may break up the π system of organics and extinct fluorescence (Zanca et al, 2017). It could be inferred that ambient WSOCs tended to exhibit higher AFI/WSOC ratios, whereas both freshly emitted WSOCs and completely oxidized WSOCs could lead to lower AFI/WSOC values.…”

Reactive Uptake of Isoprene Epoxydiols Increases the Viscosity of the Core of Phase-Separated Aerosol Particles

“…To establish photooxidation conditions, the O 3 was photolyzed at λ of 254 nm inside the OFR to generate O­( 1 D) radicals, which reacted with H 2 O to continuously produce hydroxyl (OH) radicals ([OH] ≈ 10 10 cm –3 ). Recent studies suggest that SOA particles generated in OFRs have compositions similar to SOA generated in environmental chambers ,− and in the atmosphere. − …”

Pathogenic Mechanisms of Secondary Organic Aerosols

“…Another study reported increased RNA oxidation in cells exposed to SOA resulting in transcript alteration and cell function disruption . Some molecules namely cinnamic acid, hydroxybenzoic acid, and 1,4-naphtaquinone were found in SOA, − and they or their derivatives have been reported to induce apoptosis and autophagy in multiples cancer cells lines. − …”