Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session B34: Environmental Interfaces II |
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Sponsoring Units: DCP Chair: Vicki Grassian, University of Iowa Room: LACC 511A |
Monday, March 21, 2005 11:15AM - 11:51AM |
B34.00001: Reactions at Interfaces in the Lower Atmosphere: Current Problems and Future Challenges Invited Speaker: It is increasingly recognized that reactions at interfaces play key roles in the chemistry of the lower atmosphere. These include reactions at air-liquid interfaces such as sea salt particles as well as processes at air-solid interfaces such as mineral dust particles. Organics from anthropogenic and biological sources are believed to be ubiquitous components of such particles. Previous studies suggest that the reaction of ozone with unsaturated organics at such interfaces is faster than expected by analogy to the gas phase reactions. We report here the results of kinetic and mechanistic studies of the reactions of gas phase ozone at room temperature with alkene self-assembled monolayers (SAMs) in the absence and presence of water vapor. A combination of attenuated total reflectance (ATR) and transmission FTIR as well as non-contact AFM was used to probe the chemistry. The kinetics, mechanisms and the implications for oxidation of organics on surfaces under atmospheric conditions, and future challenges, will be discussed. [Preview Abstract] |
Monday, March 21, 2005 11:51AM - 12:03PM |
B34.00002: Photodissociation action spectroscopy of ozonized films of undecylenic acid Anthony Gomez, Ao Li, Maggie Wlaser, Nicole Britigan, Sergey Nizkorodov Photochemical studies of thin films of oxidized undecylenic acid and its salts will be presented. The films are first partially oxidized by ozone, and then irradiated with a wavelength tunable UV source in an inert atmosphere. The escaping gas-phase photochemical products are detected by cavity ring-down spectroscopy as a function of the excitation frequency. The film composition is analyzed by chromatography and mass spectrometry. The data provide critical new insights into the mechanisms of ozonolysis and photolysis of oxidized undecylenic acid, and have serious implications for atmospheric chemistry of organic aerosol particles. [Preview Abstract] |
Monday, March 21, 2005 12:03PM - 12:15PM |
B34.00003: Structure of Aqueous Organic Nanodroplets from Density Functional Theory G. Wilemski, J.-S. Li Aqueous aerosol droplets play a major, but poorly quantified role in atmospheric radiative forcing. To understand this role better, detailed knowledge of microscopic droplet properties is needed. We use density functional theory to study binary nanodroplets for a model system resembling an aqueous pentanol mixture. The model is a binary mixture of hard spheres with attractive Yukawa forces whose parameters are chosen to give rough agreement with measured vapor pressures, densities, and surface tensions of pure bulk water and pentanol at 250 K. The model properly predicts bulk liquid-liquid phase separation at small pentanol concentrations. Nanodroplet composition, structure, and size (1 nm to 30 nm) were studied by varying the vapor phase composition and pressure. At low pentanol vapor compositions, the nanodroplets have water-rich cores surrounded by a thin pentanol-rich shell. At high pentanol vapor concentrations, the droplets are nearly uniform binary mixtures with an outer layer of pure pentanol. The phase boundary for the core-shell region is not described well by classical thermodynamics. This failure highlights the importance of using nonclassical approaches to investigate the behavior of multicomponent aerosol droplets. [Preview Abstract] |
Monday, March 21, 2005 12:15PM - 12:51PM |
B34.00004: Uptake Kinetics of Trace Gases on Aqueous and Organic Droplets Invited Speaker: Submicron atmospheric particles are now know to frequently contain significant levels of aliphatic, aromatic, and/or partially oxygenated organic species. The interaction of atmospheric trace gases with organic and aqueous/organic particle surfaces may have important impacts on atmospheric chemistry and aerosol/cloud microphysics processes. A droplet train/fast flow reactor technique has been used to investigate the uptake kinetics of reactive and/or condensable inorganic and organic vapor species with ethylene glycol, 1-octanol and 1-methylnaphthalene surfaces as a function of relative humidity. The trace vapor uptake kinetics on these surfaces will be compared and contrasted with the kinetics of trace gas uptake on aqueous droplets. [Preview Abstract] |
Monday, March 21, 2005 12:51PM - 1:03PM |
B34.00005: An ambient FTIR study of small molecules on MgO(100) as a model for dust interactions in the troposphere Michelle Foster Magnesium oxide is a model basic oxide, having a simple rock-salt structure, a single valence state, only one stable low-index surface orientation-the (100) face, and most importantly, it is transparent in the infrared. So while MgO is not a common mineral found in tropospheric dust, it can be used as a model substrate for studies of adsorption and reactions on tropospheric dust particles. I have investigated the dynamic equilibrium occurring between MgO(100) surfaces and a series of small molecules, including water, methanol and acetic acid, in an attempt to model the role played by metal oxide surfaces in heterogeneous tropospheric chemistry. A sample cell has been constructed such that many of these infrared transparent surfaces are investigated. The adsorbate of interest is introduced at the desired pressure and allowed to establish a dynamic equilibrium with the MgO(100). The adlayer formed on the crystal faces is observed by transmission-FTIR spectroscopy, and a quantitative determination of adlayer coverages is determined using a modified Beer-Lambert Law. The substrates have also been inspected with atomic force microscopy (AFM) both before and after each series of experiments. The interactions of these adsorbates with MgO(100) under room temperature conditions and pressures on the order of 10 Torr vary from physisorbed, as is the case with methanol all the way up to dissociatively chemisorbed, as is the case with acetic acid. [Preview Abstract] |
Monday, March 21, 2005 1:03PM - 1:15PM |
B34.00006: Wetting phenomena and lateral adhesion Rafael Tadmor, Prashant Bahadu, Preeti Yadav, Alexandra Azacor, Carl Jinkins Surface energies are key factors in many physical problems but they are often difficult to determine. A straightforward way to determine surface energies is by placing a drop on the surface of interest and using the Young equation and the recently obtained relation between the Young contact angle and the maximal advancing, \textit{$\theta $}$_{A}$, and minimal receding, \textit{$\theta $}$_{R}$, contact angles$^{1}$ to extract the surface energy of the surface. We present here some ways to measure the two extremes contact angles and discuss the related lateral adhesion. 1. R. Tadmor, \textit{Langmuir}\textbf{, }$20, $7659-7664, \textbf{2004.} [Preview Abstract] |
Monday, March 21, 2005 1:15PM - 1:51PM |
B34.00007: Surface Chemistry at Size-Selected Nano-Aerosol Particles Invited Speaker: A method has been developed to conduct surface chemistry and extract surface kinetic rates from size-selected aerosol nanoparticles. The measurements encompass broad ranges of particle size, phase, and composition. Results will be presented on the uptake of water by aerosolized soot nanoparticles of radius between 10 and 40 nm. Water uptake was monitored by tandem differential mobility analysis (T-DMA), which is capable of measuring changes in particle diameter as little as 0.2 nm. Soot particles were produced in an ethene diffusion flame and extracted into an atmospheric pressure aerosol flow tube reactor. The particles were subjected to various thermal and oxidative treatments, and the effects of these treatments on the ability of soot to adsorb monolayer quantities of water was determined. The results are important because soot nucleates atmospheric cloud particles. More generally, the results represent one of the first kinetic and mechanistic studies of gas-phase nanoparticle reactivity. \newline \newline Co-author: Henry Ajo, University of Minnesota [Preview Abstract] |
Monday, March 21, 2005 1:51PM - 2:03PM |
B34.00008: Heterogeneous Reactions in Atmospheric Aerosols Observed Using ATOFMS Sullivan Ryan, Sergio Guazzotti, John Holecek, Matthew Spencer, Kimberly Prather The heterogeneous aging of natural atmospheric particles by reactive gases in the troposphere has been investigated in a flow-tube reactor using Aerosol Time-of-Flight Mass Spectrometry (ATOFMS) to monitor changes in the particle composition in real-time. Sea- salt and mineral dust aerosols were introduced into the flow tube simultaneously and reacted with nitric acid in a relative rate experiment. ATOFMS is a single-particle technique and thus enables us to distinguish which particle type accumulates more nitric acid. This allows us to determine if the differing surface area or kinetics is driving the partitioning of nitric acid between the sea salt and dust. The results of these and other aerosol flow-tube kinetics experiments will be presented.Ê The atmospheric implications will be emphasized, particularly in relation to observations made by ATOFMS of heterogeneous reactions occurring in particles over the Pacific Ocean during ACE-Asia. [Preview Abstract] |
Monday, March 21, 2005 2:03PM - 2:15PM |
B34.00009: Nonlinear optical probe of molecular structure on colloidal particle surfaces Shih-Hui Jen, Heather Eckenrode, Jun Han, Hai-Lung Dai The structure of molecules adsorbed at the colloidal particle surface has great influence on how the colloidal particles interact among themselves and with the environment. In this presentation we show that Second Harmonic Generation from molecules adsorbed at the particle surface can be used for determining the orientation of the molecules at this buried interface. The determination is facilitated by nonlinear Rayleigh-Gans-Debye analysis of polarization and scattering angle dependent SHG. The first demonstration is performed on the cationic Malachite Green (MG) molecule adsorbed on three types of polystyrene microspheres with different surface composition and charges. [Preview Abstract] |
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