New insights into the chemical composition and formation mechanisms of secondary organic aerosols produced in the ozonolysis of limonene

Limonene is a wide-spread volatile organic compound in the atmosphere. Its fast reaction with ozone leads to a large range of low-volatility oxygenated products that can form aerosols through gas-to-particle conversion processes. However, the physical and chemical mechanisms at the origin of particle formation are still fairly unknown despite the general importance of atmospheric aerosols towards health and climate. In the present work, we combined experimental and theoretical approaches to potentially decipher new significant mechanisms in the ozonolysis of limonene. After a thorough analysis of secondary organic aerosol (SOA) chemical composition highlighting for the first time the formation of oligomers up to heptamer structures as well as linear organic diacids, we proposed a formation mechanism involving non-covalent hydrogen bonding implying carboxylic/carbonyl/hydroxy groups. Theoretical quantum chemical calculations on dimers and trimers confirmed the stability of such structures. Thus, the present results highlight the formation of large oligomeric molecules whose atmospheric fate and health impacts need to be investigated. More generally, it is suggested that these non-covalent H-bonds play a role in the first steps of SOA formation from terpene oxidation in the atmosphere.