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.

The Oxidation of Oleate in Submicron Aqueous Salt Aerosols: Evidence of a Surface Process

“…12,[28][29][30][31][32][33][34][35][36] Several factors have motivated these studies, including: quantifying the time scale for organic aerosol to be converted from hydrophobic to hydrophilic via oxidation thereby influencing their CCN ability, estimating the lifetime of unsaturated organics in aerosol particles, and evaluating organic aerosol oxidation as a potential source of volatile organics. The reaction has been studied using pure oleic acid aerosols, [37][38][39][40][41][42][43][44][45] 2-30 nm thick films on polystyrene beads, 46 ∼1 µm thick films on aqueous sea salt aerosol 47 and on macroscopic films in coated wall flow tube studies. [48][49][50][51][52] Both volatile and involatile products of oleic acid ozonolysis have been identified, including nonanaldehyde, nonanoic acid, 9-oxononanoic acid, and azelaic acid.…”

The ozonolysis of primary aliphatic amines in fine particles

“…The products of this secondary chemistry generally stem from the high reactivity of stabilized Criegee intermediates (SCI) and include high molecular weight, peroxidic oligomers (Reynolds et al, 2006;Hung and Ariya, 2007;Zahardis et al, 2006a;Katrib et al, 2005;Hung et al, 2005;Gross et al, 2006;Hearn et al, 2005;Ziemann, 2005). These types of products may have a role in the experimentally observed increase in hygroscopicity and CCN activation of fine organic particles with ozonation (Broekhuizen et al, 2004;Shilling et al, 2007;King et al, 2004;Hung and Ariya, 2007). Conversely, DOS and similar high molecular weight esters (i.e.…”

In situ Quantification of Ammonium Sulfate in Single Aerosol Droplets by Means of Laser Trapping and Raman Spectroscopy

“…An optical trapping-microspectroscopy (absorption/emission/ Raman) technique is the fundamental basis for studying aerosol droplets, since the technique can manipulate and interrogate an arbitrary sized single droplet in the gas phase. [1][2][3][4][5][6][7][8] However, since micrometer-sized aerosol droplets easily evaporate and quickly disappear in air, the number of reports on the optical trapping of aerosol microparticles is still limited compared with that of colloidal particles (i.e., microparticles in a liquid phase). 9 As we showed in a previous publication, the noncontact levitation of a single micrometer-sized water droplet in air can be achieved by a laser trapping technique.…”