Aqueous-phase aerosols on the air-water interface: Response of fatty acid Langmuir monolayers to atmospheric inorganic ions.

Atmospheric aerosol particles composed of a mixture of organic and inorganic compounds are common and constitute an important fraction of air pollutants. In this study, the activities of common atmospheric inorganic ions (Ag+, Zn2+, Fe3+, Fe2+, Ca2+ and Al3+) and fatty acid molecules (stearic acid and arachidic acid) at air-aqueous interface were investigated by Langmuir methods and infrared reflection-absorption spectroscopy (IRRAS). In the presence of different inorganic ions, surface pressure-area isotherms of the Langmuir films showed compressed or expanded characteristics. IRRAS spectra confirmed that the existence of inorganic ions in the fatty acid monolayer changes the surface properties of aqueous-phase aerosols. Formation of different coordination types of carboxylates at the air-water interface alters the dissolution and partitioning behavior, which has significant influence of Raoult effect on nucleating cloud droplets. Our work displays the relationship between structure and surface properties for aqueous-phase aerosols and implies an efficient method for further understanding of their formation mechanism and potential atmospheric implications.