Enhanced Volatile Organic Compounds emissions and organic aerosol mass increase the oligomer content of atmospheric aerosols

Abstract

Secondary organic aerosol (SOA) accounts for a dominant fraction of the submicron atmospheric particle mass, but knowledge of the formation, composition and climate effects of SOA is incomplete and limits our understanding of overall aerosol effects in the atmosphere. Organic oligomers were discovered as dominant components in SOA over a decade ago in laboratory experiments and have since been proposed to play a dominant role in many aerosol processes. However, it remains unclear whether oligomers are relevant under ambient atmospheric conditions because they are often not clearly observed in field samples. Here we resolve this long-standing discrepancy by showing that elevated SOA mass is one of the key drivers of oligomer formation in the ambient atmosphere and laboratory experiments. We show for the first time that a specific organic compound class in aerosols, oligomers, is strongly correlated with cloud condensation nuclei (CCN) activities of SOA particles. These findings might have important implications for future climate scenarios where increased temperatures cause higher biogenic volatile organic compound (VOC) emissions, which in turn lead to higher SOA mass formation and significant changes in SOA composition. Such processes would need to be considered in climate models for a realistic representation of future aerosol-climate-biosphere feedbacks.

Particle size dependence of biogenic secondary organic aerosol molecular composition

“…In this regard, elemental analysis shows that ambient SOA is generally more highly oxidized than laboratory SOA (Aiken et al, 2008). Also, molecular analysis of ambient samples shows that oligomer ions tend to have very low signal intensities (Mentel et al, 2015), though higher oligomer signal intensities appear to be strongly correlated with CCN activity (Kourtchev et al, 2016). The results we present here illustrate the potential impact that particle phase chemistry can have on SOA formation and the particle size range where this chemistry becomes important.…”

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

“…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. It was also demonstrated in the latter study that the oligomer content is strongly correlated with cloud condensation nuclei activities of SOA particles.…”

Ambient observations of dimers from terpene oxidation in the gas phase: Implications for new particle formation and growth

“…Observations suggest that the contribution to SOA mass is greater from dimer‐like components than trimers, etc. [ Kourtchev et al ., ]. Proposed molecular formulae of such oligomers reveal O:C ratios that put them close to or even into to the HOM category and are indicative of their low or even extremely low volatile nature [ Gao et al ., ; Iinuma et al ., ; Kristensen et al ., , ; Yasmeen et al ., ].…”