title: Laser tweezers Raman study of optically trapped aerosol droplets of seawater and oleic acid reacting with ozone: implications for cloud-droplet properties.
abstract: In this communication we report the first use of the Raman laser tweezers technique to trap and hold a mixed droplet of oleic acid and water at atmospheric pressure for 30 min, oxidize the oleic acid on the droplet, follow the decay of reactants and the growth of chemical products using Raman spectroscopy, and monitor the growth in size of the droplet as it becomes more hydrophilic. We demonstrate that the oxidation of organic films on water droplets could have large climatic effects in the atmosphere. We show that cloud-droplet growth and activation of cloud condensation nuclei (to become cloud droplets) is retarded by the presence of an organic film and that chemical oxidation of this film would allow a cloud droplet to grow, reducing cloud albedo by inducing precipitation, and would allow a cloud condensation nucleus to grow to a cloud droplet, thus forming a cloud and increasing the albedo of the Earth.
authors.affiliation: Department of Geology, Royal Holloway University of London, Egham, Surrey TW20 0EX, U.K.
authors.forename: Martin D
authors.initials: MD
authors.lastname: King
authors.forename: Katherine C
authors.initials: KC
authors.lastname: Thompson
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Ward