Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session W26: Focus Session: Advances in Atmospheric Aerosol Science IV |
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Sponsoring Units: DCP Chair: Laura Voss, Bowdoin College Room: Morial Convention Center 218 |
Thursday, March 13, 2008 2:30PM - 3:06PM |
W26.00001: "The optics of atmospheric aerosol particles" Invited Speaker: |
Thursday, March 13, 2008 3:06PM - 3:42PM |
W26.00002: The Molecular Picture Behind Resonance Phenomena in Aerosol Spectra Invited Speaker: The study of icy aerosol particles with sizes in the submicron range is a highly interdisciplinary subject at the junction of nanosciences, atmospheric physics, and astrophysics. The microphysics of aerosol clouds in the atmospheres of planets and their moons, such as ammonia clouds on Jupiter and Saturn or methane aerosols on Titan, is currently very much in the focus of the scientific community. Particularly broad interest has been sparked by the recent Cassini-Huygens mission to Saturn's moon Titan, which has illuminated the importance of methane clouds for Titan's weather and their analogy to the role of water ice clouds in Earth's atmosphere. The present contribution focuses on the influence of intrinsic particle properties, such as shape, size or architecture, on infrared optical properties of icy aerosol particles. Intrinsic particle properties manifest themselves in mid-infrared extinction spectra by modifying the structure of vibrational bands. We ultimately aim at unravelling the microscopic origin of the characteristic patterns found in the spectra of these weakly bound molecular aggregates. To this end we compare our experimental results with different model calculations combining molecular dynamics simulations with vibrational quantum dynamics. [Preview Abstract] |
Thursday, March 13, 2008 3:42PM - 3:54PM |
W26.00003: Investigations of Hygroscopic Growth and Phase Transitions of Atmospheric Particles by Noncontact Atomic Force Microscopy (AFM). Benjamin Ocko, Susan Oatis, Matthew Strasberg, Stephen Schwartz, Antonio Checco Aerosol particles (nanometer to micrometer sized particles suspended in air) affect atmospheric radiation and cloud microphysics. A correct description of their behavior in the atmosphere is essential to accurate climate modeling. The processes by which initially hydrophobic particles become hygroscopic, accrete water from the vapor, undergo phase transition from solid particles to solution droplets are important but not well understood at a fundamental level. We have carried out AFM studies to measure changes in particle size and morphology as a function of the relative humidity for particles of sodium chloride (a substance whose bulk hygroscopic properties are well characterized) deposited on substrates with differing surface energies (Silicon Oxide, Carboxy- and Methyl-terminated organic thin-films). For particles with height $>$ 50 nm, deliquescence was observed with a relative humidity near 75{\%} ($\pm $2{\%}), is consistent with measurements of suspended aerosols. These preliminary results demonstrate that environmental AFM is a viable probe for studying the hygroscopic behavior of salt nanoparticles on solid supports. Supported by the U.S. Department of Energy, DE-AC02-98CH. [Preview Abstract] |
Thursday, March 13, 2008 3:54PM - 4:06PM |
W26.00004: Extinction by Single and Multiple Particles Matthew Berg, Christopher Sorensen, Amit Chakrabarti The combined effect of scattering and absorption is referred to as extinction and is responsible for the redistribution of radiant energy by a particle. This presentation will show that extinction is due to wave interference. Simulations of the energy flow caused by the interference graphically demonstrate how extinction redistributes the energy of incident light. Both single and multi-particle systems are considered. A conceptual, phase-based explanation is given that builds on previous work and illustrates the physical meaning of the optical theorem. Implications regarding the measurement of extinction are discussed. [Preview Abstract] |
Thursday, March 13, 2008 4:06PM - 4:18PM |
W26.00005: Scattering Patterns for Spherical and Non-spherical Particles Christopher Sorensen Aerosols affect our climate directly by scattering and absorbing light. These optical properties depend on the size, shape, and composition. We have recently described patterns that appear in the phase function for spherical particles, Mie scattering, when the scattered intensity is plotted versus the scattering wave vector q = 2ksin(theta/2) [1, 2]. These patterns involve three different power law regimes and a quasi- universality on the phase-shift parameter rho= 2kR(m-1), where R is the radius and m the refractive index. Similar patterns appear for non-spherical particles. These patterns give us an empirical description of scattering by particles of arbitrary shape and refractive index. In other work we have explored the consequences of symmetry or its lack on polarization and backscattering. These results can be useful for predicting the scattering of atmospheric aerosol particles. [1] C.M. Sorensen and D.F. Fischbach, Opt. Commun. 173,145 (2000). [2] M.J. Berg, C.M. Sorensen, and A. Chakrabarti, Applied Optics 44, 7487-7493 (2005). I acknowledge very useful collaborations with M. Berg and A. Chakrabarti. [Preview Abstract] |
Thursday, March 13, 2008 4:18PM - 4:54PM |
W26.00006: Understanding aerosol-cloud interactions Invited Speaker: The effects of aerosols on clouds (known as the ``aerosol indirect climatic effect'') are thought to have a net climatic cooling effect which partially offsets greenhouse gas warming. Regional impacts of aerosols on precipitation and cloudiness can be even stronger. Despite its importance, the complex and multi-scale nature of aerosol-cloud interactions makes quantitative assessments of the indirect effect one of the most uncertain components of anthropogenic climate change. This talk will present the approaches used to observationally study them and represent them in models. We will provide an assessment of what has been learned and point out key research challenges for the future. [Preview Abstract] |
Thursday, March 13, 2008 4:54PM - 5:06PM |
W26.00007: Alkyl Polyoxyethylene Surfactant Residue Distribution after Sessile Droplet Evaporation. Kwaichow Chan, Scott Pierce, Yunji Mi, Heping Zhu Post-evaporation residues of an Alkyl Polyoxyethylene surfactant on a slightly hydrophilic surface are studied. ~An edge-detecting contrast recognition algorithm is used to measure the areas of small (7-30$\mu $m diameter) surfactant ``islands'' which form during the evaporation process as a result of flows within the droplet and surface tension gathering. ``Island'' distributions broaden with increased concentration, accompanied by higher mean interior island size. Fitting the histogram of island sizes beginning with the principle peak reveals a general form: $y=(6\times 10^8)Cx^{-\alpha}$ where y is frequency, $C$ the concentration and \textit{$\alpha $ }is a constant having value between 2.55 and 3.00. Log-log plots evidence a linear behaviour over two orders of magnitude. Total area covered does not increase in a linear fashion with concentration, as one may expect. Rather, a ``critical'' concentration is achieved at approximately 0.15{\%}, above which area increase is less pronounced. [Preview Abstract] |
Thursday, March 13, 2008 5:06PM - 5:18PM |
W26.00008: ABSTRACT WITHDRAWN |
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