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Loukonen V.,University of Helsinki | Kurten T.,University of Helsinki | Ortega I.K.,University of Helsinki | Vehkamaki H.,University of Helsinki | And 3 more authors.
Atmospheric Chemistry and Physics

We have studied the hydration of sulfuric acid - ammonia and sulfuric acid - dimethylamine clusters using quantum chemistry. We calculated the formation energies and thermodynamics for clusters of one ammonia or one dimethylamine molecule together with 1-2 sulfuric acid and 0-5 water molecules. The results indicate that dimethylamine enhances the addition of sulfuric acid to the clusters much more efficiently than ammonia when the number of water molecules in the cluster is either zero, or greater than two. Further hydrate distribution calculations reveal that practically all dimethylamine-containing two-acid clusters will remain unhydrated in tropospherically relevant circumstances, thus strongly suggesting that dimethylamine assists atmospheric sulfuric acid nucleation much more effectively than ammonia. © 2010 Author(s). Source

Hagen M.,German Aerospace Center | Van Baelen J.,CNRS Laboratory of Physics and Meteorology | Richard E.,CNRS Laboratory for Aerology
Quarterly Journal of the Royal Meteorological Society

A number of days with small precipitating convective cells were investigated using weather radars during the COPS (Convective and Orographically-induced Precipitation Study) field campaign in the region of the Vosges and the Rhine Valley in Central Europe. Depending on the weather situation, two distinct mechanisms could be identified for the initiation of convection. On some days, cells were initiated over the ridge of the Vosges, whereas on other days cells were initiated in the lee of the Vosges. The initiation of convection appeared to be concentrated in a few favourable locations. Using the Froude number, it was possible to describe the two distinct mechanisms. When the Froude number was low, the flow was diverted around the Vosges and thermally driven convergence at the ridge initiated convection, whereas when the Froude number was high, the flow passed through mountain gaps and then converged on the lee side with the flow in the Rhine Valley. The convergence on the lee side was enhanced at locations where the outflows through valleys converged. Low Froude numbers were accompanied by weak winds varying with height, whereas high Froude numbers were observed during situations with stronger southwesterly winds increasing with height. Copyright © 2011 Royal Meteorological Society Copyright © 2011 Royal Meteorological Society. Source

Adachi K.,Arizona State University | Freney E.J.,Arizona State University | Freney E.J.,CNRS Laboratory of Physics and Meteorology | Buseck P.R.,Arizona State University
Geophysical Research Letters

Hygroscopic aerosol particles change the magnitude of light scattering through condensation and evaporation of water vapor. We collected aerosol particles from two megacities and observed the particle shapes at various values of relative humidity (RH) using an environmental cell within a transmission electron microscope. Many Mexico City samples had sulfate particles that were embedded within weakly hygroscopic organic aerosol, whereas the Los Angeles samples mainly consisted of externally mixed sulfate particles. For the Mexico City samples, when the RH was increased in the microscope, only the sulfate parts deliquesced, but the entire particle did not become spherical, i.e., particles containing deliquescent phases do not necessarily become spherical upon deliquescence. This result conflicts with the assumption used in many models, i.e., that deliquesced particles become spherical. Using a discrete-dipole approximation to calculate light scattering of simulated particles that resemble the observed ones, we show that, for particles >1.0 m, the spherical-shape assumption used in Mie theory underestimates the light scattering by ∼50%, with the exact value depending on the sizes and relative volumes of the constituent phases. © 2011 by the American Geophysical Union. Source

Dalou C.,CNRS Magmas and Volcanoes Laboratory | Koga K.T.,CNRS Magmas and Volcanoes Laboratory | Shimizu N.,Woods Hole Oceanographic Institution | Boulon J.,CNRS Laboratory of Physics and Meteorology | Devidal J.-L.,CNRS Magmas and Volcanoes Laboratory
Contributions to Mineralogy and Petrology

We experimentally determined F and Cl partition coefficients together with that of 19 trace elements (including REE, U-Th, HFSE and LILE) between basaltic melt and lherzolite minerals: olivine, orthopyroxene, clinopyroxene, plagioclase and garnet. Under conditions from 8 to 25 kbars and from 1,265 to 1,430°C, compatibilities of F and Cl are globally ordered as D Cpx/melt > D Opx/melt > D Grt/melt > D Ol/melt > D Plag/melt, and D F mineral/melt is larger than D Cl mineral/melt. Four other major results were brought to light. (1) Chlorine partition coefficients positively correlate with the jadeite component in orthopyroxene, and increase of the CaTs component promotes Cl incorporation in clinopyroxene. (2) Variations of fluorine partition coefficients correlate strongly with melt viscosity. (3) F and Cl partition coefficients correlate with the Young's modulus (E 0) of pyroxene octahedral sites (M sites) and with Raman vibrational modes of pyroxenes. This demonstrates a fundamental interaction between the M site of pyroxenes and the incorporation of F and Cl. (4) We also determined the parameters of the lattice-strain model applied to 3+ cation trace elements for the two M sites in orthopyroxene and clinopyroxene: D 0 M1, D 0 M2, r 0 M1, r 0 M2, E 0 M1 and E 0 M2. © 2011 Springer-Verlag. Source

Langmann B.,University of Hamburg | Sellegri K.,CNRS Laboratory of Physics and Meteorology | Freney E.,CNRS Laboratory of Physics and Meteorology
Atmospheric Chemistry and Physics

Until recently secondary organic carbon aerosol (SOA) mass concentrations have been systematically underestimated by three-dimensional atmospheric-chemistry-aerosol models. With a newly proposed concept of aging of organic vapours, more realistic model results for organic carbon aerosol mass concentrations can be achieved. Applying a mixed thermodynamic-kinetic approach for SOA formation shifted the aerosol size distribution towards particles in the cloud condensation nuclei size range, thereby emphasising the importance of SOA formation schemes for modelling realistic cloud and precipitation formation. The additional importance of hetero-molecular nucleation between H2SO4 and organic vapours remains to be evaluated in three-dimensional atmospheric-chemistry-aerosol models. Here a case study is presented focusing on Puy-de-Dôme, France in June 2010. The measurements indicate a considerable increase in SOA mass concentration during the measurement campaign, which could be reproduced by modelling using a simplified thermodynamic-kinetic approach for SOA formation and increased biogenic volatile organic compound (VOC) precursor emissions. Comparison with a thermodynamic SOA formation approach shows a huge improvement in modelled SOA mass concentration with the thermodynamic-kinetic approach for SOA formation. SOA mass concentration increases by a factor of up to 6 accompanied by a slight improvement of modelled particle size distribution. Even though nucleation events at Puy-de-Dôme were rare during the chosen period of investigation, a weak event in the boundary layer could be reproduced by the model in a sensitivity study when nucleation of low-volatile secondary organic vapour is included. Differences in the model results with and without nucleation of organic vapour are visible in the lower free troposphere over several days. Taking into account the nucleation of organic vapour leads to an increase in accumulation mode particles due to coagulation and condensational growth of nucleation and Aitken mode particles. © Author(s) 2014. CC Attribution 3.0 License. Source

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