Abstract/Summary

We demonstrate that fatty acids in proxies for atmospheric aerosols self-assemble into highly ordered three–dimensional nanostructures that may have implications for environmental-ly important processes. Acoustically trapped droplets of oleic acid/sodium oleate mixtures in sodium chloride solution are analysed by simultaneous synchrotron small-angle X-ray scat-tering and Raman spectroscopy in a controlled gas-phase en-vironment. We demonstrate that the droplets contained crys-tal-like lyotropic phases including hexagonal and cubic close-packed arrangements of spherical and cylindrical micelles, and stacks of bilayers, whose structures responded to atmos-pherically relevant humidity changes and chemical reactions. Further experiments show that self-assembly reduces the rate of the reaction of the fatty acid with ozone, and that lyotropic phase formation also occurs in more complex mixtures more closely resembling compositions of atmospheric aerosols. We suggest that lyotropic phase formation likely occurs in the atmosphere, with potential implications for radiative forcing, residence times and other aerosol characteristics fundamental to atmospheric research.