Molecular composition of fresh and aged secondary organic aerosol from a mixture of biogenic volatile compounds: a high-resolution mass spectrometry study

Abstract

Abstract. Field observations over the past decade indicate that a significant fraction of organic aerosol in remote areas may contain highly oxidized molecules. Aerosol processing or further oxidation (aging) of organic aerosol has been suggested to be responsible for their formation through heterogeneous reaction with oxidants and multigenerational oxidation of vapours by OH radicals. In this study we investigated the influence of several aging processes on the molecular composition of secondary organic aerosols (SOA) using direct infusion and liquid chromatography high-resolution mass spectrometry. SOA was formed in simulation chamber experiments from ozonolysis of a mixture of four biogenic volatile organic compounds (BVOC): α-pinene, β-pinene, Δ3-carene and isoprene. The SOA was subsequently aged under three different sets of conditions: in the dark in the presence of residual ozone, with UV irradiation and OH radicals, and using UV light only. Among all studied conditions, only OH radical-initiated aging was found to influence the molecular composition of the aerosol and showed an increase in carbon oxidation state (OSC) and elemental O / C ratios of the SOA components. None of the aging processes produced an observable effect on the oligomers formed from ozonolysis of the BVOC mixture, which were found to be equally abundant in both "fresh" and "aged" SOA. Additional experiments using α-pinene as the sole precursor demonstrated that oligomers are an important group of compounds in SOA produced from both ozonolysis and OH radical-initiated oxidation processes; however, a completely different set of oligomers is formed under these two oxidation regimes. SOA from the OH-initiated oxidation of α-pinene had a significantly higher overall OSC and O / C compared to that from pure ozonolysis experiments confirming that the OH radical reaction is more likely to be responsible for the occurrence of highly oxidized species in ambient biogenic SOA.

High-molecular-weight esters in <i>α</i>-pinene ozonolysis secondary organic aerosol: structural characterization and mechanistic proposal for their formation from highly oxygenated molecules

“…MW 358 and 368 esters were first reported in ambient nighttime PM with an aerodynamic diameter ≤ 2.5 µM (PM 2.5 ) that was collected at K-puszta, Hungary, during a 2006 summer campaign (Yasmeen et al, 2010). They were later detected in several field studies that were conducted in other forested environments (Kristensen et al, 2013(Kristensen et al, , 2016Kourtchev et al, 2014Kourtchev et al, , 2015. It was shown by Kourtchev et al (2016) that oligomers (i.e., hetero-oligomers) are of climatic relevance in that elevated SOA mass is one of the key drivers of oligomer formation not only in laboratory experiments but also in the ambient atmosphere.…”

Effect of relative humidity on the composition of secondary organic aerosol from the oxidation of toluene

“…Under supersaturated conditions, aqueous chemistry occurring in cloud and fog droplets promotes the conversion of small water-soluble molecules into nonvolatile products that would not form in the absence of liquid water (Herrmann et al, 2015). Finally, dissolved SOA compounds may undergo more efficient photodegradation in water (Bateman et al, 2011;Nguyen et al, 2012;Romonosky et al, 2015Romonosky et al, , 2017Zhao et al, 2017) compared to dry particles (Kourtchev et al, 2015).…”

Observations of sesquiterpenes and their oxidation products in central Amazonia during the wet and dry seasons

“…The negative ionization mass spectra were collected in three replicates over ranges m/z 100-650 and m/z 150-900 and processed using Xcalibur 2.1 software (Thermo Scientific). Chemical formulae of the form C c H h N n O o S s were made according to analysis procedures presented in Kourtchev et al (2013Kourtchev et al ( , 2015 and Zielinski et al (2018), and only ions that were observed in all three replicate extract analyses were kept for evaluation. All sample intensities were normalized to the aerosol organic carbon loading as well.…”