From volatile to non-volatile in sub second time-scales: rapid HOM formation in seemingly disparate chemical systems

During the recent decade our molecular level understanding of  secondary aerosol generation in the atmosphere has progressed tremendously. The old paradigm that ambient aerosol pre-stage formation necessitates long processing times with scarce oxidants in the atmosphere has been found flawed, and we are continuously learning how the increase in molecular oxygen content, and the corresponding decrease in vapour pressure, happen far faster than presumed. We are steadily approaching a situation where the classical “single compound, single SOA yield” type of a thinking becomes obsolete, and the mechanistic description at a molecular level is required to tackle the rapid formation of ambient secondary aerosol mass.

In the current work we have performed laboratory flow reactor experiments of monoterpene and aromatic compound (auto-)oxidation applying chemical ionization mass spectrometry (CIMS) for product detection. The experiments were complemented by high-level quantum chemical computations of the important mechanistic steps, and the energy non-accommodation was accounted for in the formation of the important intermediates (i.e., we investigated the role of excess reaction energy for the product formation). It has been learned that even in seemingly very disparate chemical systems the formation of condensable products occurs fast, often in sub-second time-scales.