Condensation of organic-inorganic vapours governs the production of ultrafine secondary marine cloud nuclei

Abstract

Ultrafine secondary marine aerosol (<100 nm), formed via gas-to-particle conversion, can make an important contribution to the number of cloud condensation nuclei in the marine boundary layer. It has long been known that the growth of ultrafine secondary marine aerosol cannot be sustained solely by condensation of the inorganic species that drive the initial nucleation, and condensation of organic vapours has been suggested as the most likely mechanism. However, the evidence from field observations had been lacking. Here we report observational evidence on the importance of the condensation of organic and inorganic vapours onto Aitken mode particles in forming cloud condensation nuclei. Further long-term analysis (over 10 years) with additional hygroscopicity growth measurements reveals that the ultrafine secondary marine aerosol growth events are driven by condensation of biogenic vapours, which leads to up to substantial increases in cloud condensation nuclei number at realistic marine cloud supersaturation.