π-π Interactions Dictate the Growth of Aromatic Organic Aerosols

Secondary organic aerosols (SOAs) constitute a substantial fraction of atmospheric aerosols, functioning as critical cloud condensation nuclei, but the SOA formation rates predicted by the current atmospheric model are lower than those determined from field observations. Recent experimental studies reveal that this missing source was partially attributed to low-oxidation functional organic compounds (LOMs). Nevertheless, theoretical investigations suggest that the contribution of LOMs is limited by their poor hydrogen-bonding capabilities. Herein, benzoic acid (BA) was selected as a typical LOM to unveil the whole process of continuous cluster growth in which the initial nucleation is initiated by strong hydrogen bonding between BA and sulfuric acid (SA), consistent with experimental observations. After initiation, as the radius of the BA cluster gradually increases to 4.5 nm, SA tends to be on the subsurface of the cluster, forming strong H-bonds with ∼3 interfacial BA molecules. Such a chelation structure of SA further enhances π-π stacking between BA molecules; therefore, the cluster formation barrier reduced by ∼1.4 eV to boost the cluster growth. Overall, our study elucidates a comprehensive understanding of the potential mechanisms underlying the sustained growth of aromatic LOM clusters, revealing the overlooked role of π-π interactions in the growth of SOA growth.