534 research outputs found
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Strong aerosol-cloud interaction in altocumulus during updraft periods: Lidar observations over central Europe
For the first time, a liquid-water cloud study of the aerosolâcloud-dynamics relationship, solely based on lidar, was conducted. Twenty-nine cases of pure liquid-water altocumulus layers were observed with a novel dual-field-of-view Raman lidar over the polluted central European site of Leipzig, Germany, between September 2010 and September 2012. By means of the novel Raman lidar technique, cloud properties such as the droplet effective radius and cloud droplet number concentration (CDNC) in the lower part of altocumulus layers are obtained. The conventional aerosol Raman lidar technique provides the aerosol extinction coefficient (used as aerosol proxy) below cloud base. A collocated Doppler lidar measures the vertical velocity at cloud base and thus updraft and downdraft occurrence. Here, we present the key results of our statistical analysis of the 2010â2012 observations. Besides a clear aerosol effect on cloud droplet number concentration in the lower part of the altocumulus layers during updraft periods, turbulent mixing and entrainment of dry air is assumed to be the main reason for the found weak correlation between aerosol proxy and CDNC higher up in the cloud. The corresponding aerosolâcloud interaction parameter based on changes in cloud droplet number concentration with aerosol loading was found to be close to 0.8 at 30â70 m above cloud base during updraft periods and below 0.4 when ignoring vertical-wind information in the analysis. Our findings are extensively compared with literature values and agree well with airborne observations
Strong aerosol-cloud interaction in altocumulus during updraft periods: Lidar observations over central Europe
For the first time, a liquid-water cloud study of the aerosolâcloud-dynamics relationship, solely based on lidar, was conducted. Twenty-nine cases of pure liquid-water altocumulus layers were observed with a novel dual-field-of-view Raman lidar over the polluted central European site of Leipzig, Germany, between September 2010 and September 2012. By means of the novel Raman lidar technique, cloud properties such as the droplet effective radius and cloud droplet number concentration (CDNC) in the lower part of altocumulus layers are obtained. The conventional aerosol Raman lidar technique provides the aerosol extinction coefficient (used as aerosol proxy) below cloud base. A collocated Doppler lidar measures the vertical velocity at cloud base and thus updraft and downdraft occurrence. Here, we present the key results of our statistical analysis of the 2010â2012 observations. Besides a clear aerosol effect on cloud droplet number concentration in the lower part of the altocumulus layers during updraft periods, turbulent mixing and entrainment of dry air is assumed to be the main reason for the found weak correlation between aerosol proxy and CDNC higher up in the cloud. The corresponding aerosolâcloud interaction parameter based on changes in cloud droplet number concentration with aerosol loading was found to be close to 0.8 at 30â70 m above cloud base during updraft periods and below 0.4 when ignoring vertical-wind information in the analysis. Our findings are extensively compared with literature values and agree well with airborne observations
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Thermodynamics of the formation of sulfuric acid dimers in the binary (H2SO4-H2O) and ternary (H2SO4-H2O-NH3) system
Sulfuric acid is an important gas influencing atmospheric new particle formation (NPF). Both the binary (H2SO4âH2O) system and the ternary system involving ammonia (H2SO4âH2OâNH3) may be important in the free troposphere. An essential step in the nucleation of aerosol particles from gas-phase precursors is the formation of a dimer, so an understanding of the thermodynamics of dimer formation over a wide range of atmospheric conditions is essential to describe NPF. We have used the CLOUD chamber to conduct nucleation experiments for these systems at temperatures from 208 to 248 K. Neutral monomer and dimer concentrations of sulfuric acid were measured using a chemical ionization mass spectrometer (CIMS). From these measurements, dimer evaporation rates in the binary system were derived for temperatures of 208 and 223 K. We compare these results to literature data from a previous study that was conducted at higher temperatures but is in good agreement with the present study. For the ternary system the formation of H2SO4·NH3 is very likely an essential step in the formation of sulfuric acid dimers, which were measured at 210, 223, and 248 K. We estimate the thermodynamic properties (dH and dS) of the H2SO4·NH3 cluster using a simple heuristic model and the measured data. Furthermore, we report the first measurements of large neutral sulfuric acid clusters containing as many as 10 sulfuric acid molecules for the binary system using chemical ionizationâatmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometry
Combined vertical-velocity observations with Doppler lidar, cloud radar and wind profiler
Case studies of combined vertical-velocity measurements of Doppler lidar, cloud radar and wind profiler are presented. The measurements were taken at the Meteorological Observatory, Lindenberg, Germany. Synergistic products are presented that are derived from the vertical-velocity measurements of the three instruments: a comprehensive classification mask of vertically moving atmospheric targets and the terminal fall velocity of water droplets and ice crystals corrected for vertical air motion. It is shown that this combination of instruments can up-value the measurement values of each single instrument and may allow the simultaneous sensing of atmospheric targets and the motion of clear air
Effect of ligand backbone on the selectivity and stability of rhodium hydroformylation catalysts derived from phospholane-phosphites
We thank the Eastman Chemical Company for funding and permission to publish. M.B. thanks the School of Chemistry and EaStCHEM for support.A study on how ligand backbone structure has an impact on selectivity, rate, and catalyst stability of hydroformylation catalysts was prompted by some longer-term stability issues being discovered for a phospholane-phosphite with a [âCH2Oâ] backbone. A series of phospholane-phosphite ligands were synthesized. Catalysts made in situ from these ligands and [Rh(acac)(CO)2] were found to give iso-butanal selectivities up to 75% at temperatures between 75 and 105 °C: the latter being a benchmark for iso-selectivity in reactions conducted at industrially meaningful temperatures. A racemic rhodium complex of a bidentate phospholane-phosphite from a tropos-biphenol with an extended backbone showed unusually high stability at high temperatures, combined with even better iso-selectivity in propene hydroformylation relative to the original complex. A related ligand with an electron-withdrawing group maintained the unusually high stability and improved activity. Characterization of the precatalysts of type [RhH(CO)2(L)] was accomplished using in situ HPIR spectroscopy and backed up by density functional theory calculations (B3PW91-D3 level) and by NMR studies; the latter showed that the variation of the backbone also had a pronounced impact on the precatalyst structure. A key finding is that it is now possible to prepare phospholane-phosphite ligands that deliver high iso-butanal selectivity and that show no signs of degradation after several days even above typical reaction temperatures. In one stability test, several kilograms of aldehydes were produced with TOF and selectivity being consistent over several days.PostprintPeer reviewe
Der virtuelle Raum als Double - oder: zur Persistenz hierarchischer Gesellschaftsstruktur im Netz
Der raumsoziologische Beitrag diskutiert, was die mit der Technologie des Internets einhergehende Virtualisierung fĂŒr eine sich Ă€ndernde Gesellschaftsordnung bedeuten kann. Anhand ihres methodologischen RaumZeit-Modells zeigt die Autorin, dass die virtuelle RealitĂ€t des Internets eine doppelte materiale Gestalt hervorbringt. Als Double ergĂ€nzt der virtuelle Raum den realen. Die Ausgangsannahme lautet, dass die bĂŒrgerlich-moderne Gesellschaft Raum als ZweidimensionalitĂ€t und als BehĂ€lter sowie Zeit als messbar und linear hervorgebracht hat. Entgegen vielfach geĂ€uĂerter EinschĂ€tzungen revolutioniert das Internet nicht Vorstellungen und Praxis von Raum und Zeit, sondern es perfektioniert die bĂŒrgerliche Konstruktion des ideal beherrschbaren Lebens. Der Hypothese folgend, dass die neuen virtuellen RealitĂ€ten verĂ€nderte MaterialitĂ€ten etablieren, werden verschiedene Zukunftsszenarien am Beispiel des GeschlechterverhĂ€ltnisses durchgespielt
Static dipole polarizability of C70 fullerene
The electronic and vibrational contributions to the static dipole
polarizability of C70 fullerene are determined using the finite-field method
within the density functional formalism. Large polarized Gaussian basis sets
augmented with diffuse functions are used and the exchange-correlation effects
are described within the Perdew-Burke-Ernzerhof generalized gradient
approximation (PBE-GGA). The calculated polarizability of C70 is 103
Angstrom^3, in excellent agreement with the experimental value of 102
Angstrom^3, and is completely determined by the electronic part, vibrational
contribution being negligible. The ratio of polarizabilities of C70 and C60 is
1.26. The comparison of polarizability calculated with only local terms (LDA)
in the PBE functional to that obtained with PBE-GGA shows that LDA is
sufficient to determine the static dipole polarizability of C70.Comment: IOP style, 1 figur
Wildfire smoke triggers cirrus formation: lidar observations over the eastern Mediterranean
The number of intense wildfires may increase further in upcoming years as a consequence of climate change. It is therefore necessary to improve our knowledge about the role of smoke in the climate system, with emphasis on the impact of smoke particles on the evolution of clouds, precipitation, and cloud radiative properties. Presently, one key aspect of research is whether or not wildfire smoke particles can initiate cirrus formation. In this study, we present lidar observations over Limassol, Cyprus, from 27Â October to 3Â November 2020, when extended wildfire smoke fields crossed the Mediterranean Basin from Portugal to Cyprus. We found strong evidence that aged smoke (organic aerosol particles) originating from wildfires in North America triggered significant ice nucleation at temperatures from â47 to â53ââC and caused the formation of extended cirrus layers. The observations suggest that the ice crystals were nucleated just below the tropopause in the presence of smoke particles serving as ice-nucleating particles (INPs). The main part of the 2â3âkm thick smoke layer was, however, in the lower stratosphere just above the tropopause. With actual radiosonde observations of temperature and relative humidity and lidar-derived smoke particle surface area concentrations used as starting values, gravity wave simulations show that the lofting of air by 100â200âm is sufficient to initiate significant ice nucleation on the smoke particles, leading to ice crystal number concentrations of 1â100âLâ1.</p
Global hybrids from the semiclassical atom theory satisfying the local density linear response
We propose global hybrid approximations of the exchange-correlation (XC)
energy functional which reproduce well the modified fourth-order gradient
expansion of the exchange energy in the semiclassical limit of many-electron
neutral atoms and recover the full local density approximation (LDA) linear
response. These XC functionals represent the hybrid versions of the APBE
functional [Phys. Rev. Lett. 106, 186406, (2011)] yet employing an additional
correlation functional which uses the localization concept of the correlation
energy density to improve the compatibility with the Hartree-Fock exchange as
well as the coupling-constant-resolved XC potential energy. Broad energetical
and structural testings, including thermochemistry and geometry, transition
metal complexes, non-covalent interactions, gold clusters and small
gold-molecule interfaces, as well as an analysis of the hybrid parameters, show
that our construction is quite robust. In particular, our testing shows that
the resulting hybrid, including 20\% of Hartree-Fock exchange and named hAPBE,
performs remarkably well for a broad palette of systems and properties, being
generally better than popular hybrids (PBE0 and B3LYP). Semi-empirical
dispersion corrections are also provided.Comment: 12 pages, 4 figure
DFT investigation of 3d transition metal NMR shielding tensors in diamagnetic systems using the gauge-including projector augmented-wave method
We present a density functional theory based method for calculating NMR
shielding tensors for 3d transition metal nuclei using periodic boundary
conditions. Calculations employ the gauge-including projector augmented-wave
pseudopotentials method. The effects of ultrasoft pseudopotential and induced
approximations on the second-order magnetic response are intensively examined.
The reliability and the strength of the approach for 49Ti and 51V nuclei is
shown by comparison with traditional quantum chemical methods, using benchmarks
of finite organometallic systems. Application to infinite systems is validated
through comparison to experimental data for the 51V nucleus in various vanadium
oxide based compounds. The successful agreement obtained for isotropic chemical
shifts contrasts with full estimation of the shielding tensor eigenvalues,
revealing the limitation of pure exchange-correlation functionals compared to
their exact-exchange corrected analogues.Comment: 56 page
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