Aeroelastic and Aerothermoelastic Behavior in Hypersonic Flow

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77151/1/AIAA-36711-537.pd

Surface-Enhanced Nitrate Photolysis on Ice

Heterogeneous nitrates photolysis is the trigger for many chemical processes occurring in the polar boundary layer and is widely believed to occur in a quasi-liquid layer (QLL) at the surface of ice. The dipole forbidden character of the electronic transition relevant to boundary layer atmospheric chemistry and the small photolysis/photoproducts quantum yields in ice (and in water) may confer a significant enhancement and interfacial specificity to this important photochemical reaction at the surface of ice. Using amorphous solid water films at cryogenic temperatures as models for the disordered interstitial air/ice interface within the snowpack suppresses the diffusive uptake kinetics thereby prolonging the residence time of nitrate anions at the surface of ice. This approach allows their slow heterogeneous photolysis kinetics to be studied providing the first direct evidence that nitrates adsorbed onto the first molecular layer at the surface of ice are photolyzed more effectively than those dissolved within the bulk. Vibrational spectroscopy allows the ~3-fold enhancement in photolysis rates to be correlated with the nitrates’ distorted intramolecular geometry thereby hinting at the role played by the greater chemical heterogeneity in their solvation environment at the surface of ice than in the bulk. A simple 1D kinetic model suggests 1-that a 3(6)-fold enhancement in photolysis rate for nitrates adsorbed onto the ice surface could increase the photochemical NO[subscript 2] emissions from a 5(8) nm thick photochemically active interfacial layer by 30%(60)%, and 2-that 25%(40%) of the NO[subscript 2] photochemical emissions to the snowpack interstitial air are released from the top-most molecularly thin surface layer on ice. These findings may provide a new paradigm for heterogeneous (photo)chemistry at temperatures below those required for a QLL to form at the ice surface

Untangling the influence of Antarctic and Southern Ocean life on clouds

Polar environments are among the fastest changing regions on the planet. It is a crucial time to make significant improvements in our understanding of how ocean and ice biogeochemical processes are linked with the atmosphere. This is especially true over Antarctica and the Southern Ocean where observations are severely limited and the environment is far from anthropogenic influences. In this commentary, we outline major gaps in our knowledge, emerging research priorities, and upcoming opportunities and needs. We then give an overview of the large-scale measurement campaigns planned across Antarctica and the Southern Ocean in the next 5 years that will address the key issues. Until we do this, climate models will likely continue to exhibit biases in the simulated energy balance over this delicate region. Addressing these issues will require an international and interdisciplinary approach which we hope to foster and facilitate with ongoing community activities and collaborations

Fostering multidisciplinary research on interactions between chemistry, biology, and physics within the coupled cryosphere-atmosphere system

The cryosphere, which comprises a large portion of Earth’s surface, is rapidly changing as a consequence of global climate change. Ice, snow, and frozen ground in the polar and alpine regions of the planet are known to directly impact atmospheric composition, which for example is observed in the large influence of ice and snow on polar boundary layer chemistry. Atmospheric inputs to the cryosphere, including aerosols, nutrients, and contaminants, are also changing in the anthropocene thus driving cryosphere-atmosphere feedbacks whose understanding is crucial for understanding future climate. Here, we present the Cryosphere and ATmospheric Chemistry initiative (CATCH) which is focused on developing new multidisciplinary research approaches studying interactions of chemistry, biology, and physics within the coupled cryosphere – atmosphere system and their sensitivity to environmental change. We identify four key science areas: (1) micro-scale processes in snow and ice, (2) the coupled cryosphere-atmosphere system, (3) cryospheric change and feedbacks, and (4) improved decisions and stakeholder engagement. To pursue these goals CATCH will foster an international, multidisciplinary research community, shed light on new research needs, support the acquisition of new knowledge, train the next generation of leading scientists, and establish interactions between the science community and society

Ice structures, patterns, and processes: A view across the ice-fields

We look ahead from the frontiers of research on ice dynamics in its broadest sense; on the structures of ice, the patterns or morphologies it may assume, and the physical and chemical processes in which it is involved. We highlight open questions in the various fields of ice research in nature; ranging from terrestrial and oceanic ice on Earth, to ice in the atmosphere, to ice on other solar system bodies and in interstellar space

How ice grows from premelting films and water droplets

Close to the triple point, the surface of ice is covered by a thin liquid layer (so-called quasi-liquid layer) which crucially impacts growth and melting rates. Experimental probes cannot observe the growth processes below this layer, and classical models of growth by vapor deposition do not account for the formation of premelting films. Here, we develop a mesoscopic model of liquid-film mediated ice growth, and identify the various resulting growth regimes. At low saturation, freezing proceeds by terrace spreading, but the motion of the buried solid is conveyed through the liquid to the outer liquid-vapor interface. At higher saturations water droplets condense, a large crater forms below, and freezing proceeds undetectably beneath the droplet. Our approach is a general framework that naturally models freezing close to three phase coexistence and provides a first principle theory of ice growth and melting which may prove useful in the geosciences.Comment: 32 pages, 10 figure

Radial Diffusion and Penetration of Gas Molecules and Aerosol Particles through Laminar Flow Reactors, Denuders, and Sampling Tubes

Flow reactors, denuders, and sampling tubes are essential tools for many applications in analytical and physical chemistry and engineering. We derive a new method for determining radial diffusion effects and the penetration or transmission of gas molecules and aerosol particles through cylindrical tubes under laminar flow conditions using explicit analytical equations. In contrast to the traditional Brown method [Brown, R. L. J. Res. Natl. Bur. Stand. (U. S.) 1978, 83, 1-8] and CKD method (Cooney, D. O.; Kim, S. S.; Davis, E. J. Chem. Eng. Sci. 1974, 29, 1731-1738), the new approximation developed in this study (known as the KPS method) does not require interpolation or numerical techniques. The KPS method agrees well with the CKD method under all experimental conditions and also with the Brown method at low Sherwood numbers. At high Sherwood numbers corresponding to high uptake on the wall, flow entry effects become relevant and are considered in the KPS and CKD methods but not in the Brown method. The practical applicability of the KPS method is demonstrated by analysis of measurement data from experimental studies of rapid OH, intermediate NO3, and slow O3 uptake on various organic substrates. The KPS method also allows determination of the penetration of aerosol particles through a tube, using a single equation to cover both the limiting cases of high and low deposition described by Gormley and Kennedy ( Proc. R. Ir. Acad., Sect. A. 1949, 52A, 163-169). We demonstrate that the treatment of gas and particle diffusion converges in the KPS method, thus facilitating prediction of diffusional loss and penetration of gases and particles, analysis of chemical kinetics data, and design of fluid reactors, denuders, and sampling lines

The adsorption of peroxynitric acid on ice between 230 K and 253 K

Peroxynitric acid uptake to ice and snow has been proposed to be a major loss process from the atmosphere with impacts on the atmospheric oxidation capacity. Here we present results from a laboratory study on the interaction of peroxynitric acid with water ice at low concentration. Experiments were performed in a coated wall flow tube at atmospheric pressure and in the environmentally relevant temperature range of 230 K to 253 K. The interaction was found to be fully reversible and decomposition was not observed. Analysis based on the Langmuir adsorption model showed that the partitioning of peroxynitric acid to ice is orders of magnitude lower than of nitric acid and similar to nitrous acid partitioning behavior. The partition coefficient (<I>K</I><sub>LinC</sub>) and its temperature dependency can be described by 3.74 × 10<sup>−12</sup> × <I>e</I><sup>(7098/<I>T</I>)</sup> [cm]. Atmospheric implications are discussed and show that the uptake to cirrus clouds or to snow-packs in polar areas is an important sink for peroxynitric acid in the environment

HONO and NO₂ evolution from irradiated nitrate-doped ice and frozen nitrate solutions

International audienceNitrate photolysis in the wavelength range 250?1200 nm was studied on ice in a controlled laboratory experiment. Monolayer coverage of nitrate was achieved by dosing well-known amounts of HNO3 from the gas phase onto a frozen water surface. Fluxes of HONO and NO2 into the gas phase with time were quantified at temperatures between 193 K and 258 K and as a function of illumination wavelength in the range: 250?345 nm. Whereas HONO release showed a strong temperature dependence at colder temperatures, attributed to reversible adsorption processes, NO2 fluxes were independent of temperature. The observed fluxes of HONO and NO2 at high temperature were not affected by diffusion or adsorption processes, and could be used to estimate a quantum yield for HONO formation of (3.8±0.6)×10?4. A different wavelength dependence for HONO and NO2 fluxes indicates that additional reactions besides nitrate photolysis and subsequent release of the products contribute to the emission of nitrogen oxides