Properties of long-chain organic films as proxies for organically coated atmospheric aerosols.

摘要

Organic surfactants have been found to comprise a significant fraction of the organic content of atmospheric aerosols. While their presence on the surfaces of aerosols has been documented, the effects of these surfactants on the aerosol's properties are not well known. The physical, chemical, and optical properties of an aerosol are dependent upon the properties of the species that reside at its surface. The studies outlined here were designed to investigate the physical and chemical properties of organic films and their effects on the properties of organically coated atmospheric aerosols. The chemical systems in these laboratory studies were chosen to represent atmospherically relevant aqueous-organic-air interfaces.; The ability of the air-water interface to concentrate, select, and stabilize organic surfactants was examined as a function of the molecular properties of the surfactants and the composition of the subphase. The results of the interfacial selectivity and stability studies give valuable insight as to the formation and stability of the surfactant films and their evolution as the aerosol ages.; The effect of the organic film on the transfer of volatile organics across the air-aqueous interface was investigated. The permeability of acetic acid through pure and mixed films of long-chain organics was determined as a function of the composition of the film. The atmospheric consequences of the decreased vapor-to-particle transfer rate could affect the aerosol's bulk composition and alter some heterogeneous reactions.; The processing of saturated and unsaturated hydrocarbon films by O 3 and OH was studied. The resultant film was highly oxidized and complex in composition. This chemical evolution will affect the aerosol's size and composition as well as its hygroscopicity and optical properties.; The bulk composition of field-collected aerosols was analyzed revealing a significant content of high molecular weight, highly polar compounds. These preliminary results illustrate the presence of these compounds on aerosols. The results of these studies give valuable insight as to how the surfactant and subphase properties will ultimately affect the aging, reactivity, hygroscopicity, optical and chemical properties of an aerosol coated in such films.