Analysis of the global atmospheric background sulfur budget in a multi-model framework

Sulfate aerosol in the stratosphere is an important climate driver, causing solar dimming in the years after major volcanic eruptions. Hence, a growing number of general circulation models are adapting interactive sulfur and aerosol schemes to improve the representation of relevant chemical processes and associated feedbacks. However, uncertainties of these schemes are not well constrained. Stratospheric sulfate is modulated by natural emissions of sulfur-containing species, including volcanic eruptive, and anthropogenic emissions. Model intercomparisons have examined the effects of volcanic eruptions, whereas the background conditions of the sulfur cycle have not been addressed in a global model intercomparison project. Assessing background conditions in global models allows us to identify model discrepancies as they are masked by large perturbations such as volcanic eruptions, yet may still matter in the aftermath of such a disturbance. Here, we analyze the atmospheric burden, seasonal cycle, and vertical and meridional distribution of the main sulfur species among nine global atmospheric aerosol models that are widely used in the stratospheric aerosol research community. We use observational and reanalysis data to evaluate model results. Overall, models agree that the three dominant sulfur species in terms of burdens (sulfate aerosol, OCS, and SO2) make up about 98 % of stratospheric sulfur and 95 % of tropospheric sulfur. However, models vary considerably in the partitioning between these species. Models agree that anthropogenic emission of SO2 strongly affects the sulfate aerosol burden in the Northern Hemispheric troposphere, while its importance is very uncertain in other regions. The total deposition of sulfur varies among models, deviating by a factor of two, but models agree that sulfate aerosol is the main form in which sulfur is deposited. Additionally, the partitioning between wet and dry deposition fluxes is highly model dependent. We investigate the areas of greatest variability in the sulfur species burdens and find that inter-model variability is low in the tropics and increases towards the poles. Seasonality in the southern hemisphere is depicted very similar among models. Differences are largest in the dynamically active northern hemispheric extratropical region, hence some of the differences could be attributed to the differences in the representation of the stratospheric circulation among underlying general circulation models. This study highlights that the differences in the atmospheric sulfur budget among the models arise from the representation of both chemical and dynamical processes, whose interplay complicates the bias attribution. Several problematic points identified for individual models are related to the specifics of the chemistry schemes, model resolution, and representation of cross-tropopause transport in the extratropics. Further model intercomparison research is needed focusing on the clarification of the reasons for biases, given also the importance of this topic for the stratospheric aerosol injection studies.</p

Spectrum of mutations in Italian patients with familial hypercholesterolemia: New results from the LIPIGEN study

Background Familial hypercholesterolemia (FH) is an autosomal dominant disease characterized by elevated plasma levels of LDL-cholesterol that confers an increased risk of premature atherosclerotic cardiovascular disease. Early identification and treatment of FH patients can improve prognosis and reduce the burden of cardiovascular mortality. Aim of this study was to perform the mutational analysis of FH patients identified through a collaboration of 20 Lipid Clinics in Italy (LIPIGEN Study). Methods We recruited 1592 individuals with a clinical diagnosis of definite or probable FH according to the Dutch Lipid Clinic Network criteria. We performed a parallel sequencing of the major candidate genes for monogenic hypercholesterolemia (LDLR, APOB, PCSK9, APOE, LDLRAP1, STAP1). Results A total of 213 variants were detected in 1076 subjects. About 90% of them had a pathogenic or likely pathogenic variants. More than 94% of patients carried pathogenic variants in LDLR gene, 27 of which were novel. Pathogenic variants in APOB and PCSK9 were exceedingly rare. We found 4 true homozygotes and 5 putative compound heterozygotes for pathogenic variants in LDLR gene, as well as 5 double heterozygotes for LDLR/APOB pathogenic variants. Two patients were homozygous for pathogenic variants in LDLRAP1 gene resulting in autosomal recessive hypercholesterolemia. One patient was found to be heterozygous for the ApoE variant p.(Leu167del), known to confer an FH phenotype. Conclusions This study shows the molecular characteristics of the FH patients identified in Italy over the last two years. Full phenotypic characterization of these patients and cascade screening of family members is now in progress

Familial hypercholesterolemia: The Italian Atherosclerosis Society Network (LIPIGEN)

BACKGROUND AND AIMS: Primary dyslipidemias are a heterogeneous group of disorders characterized by abnormal levels of circulating lipoproteins. Among them, familial hypercholesterolemia is the most common lipid disorder that predisposes for premature cardiovascular disease. We set up an Italian nationwide network aimed at facilitating the clinical and genetic diagnosis of genetic dyslipidemias named LIPIGEN (LIpid TransPort Disorders Italian GEnetic Network). METHODS: Observational, multicenter, retrospective and prospective study involving about 40 Italian clinical centers. Genetic testing of the appropriate candidate genes at one of six molecular diagnostic laboratories serving as nationwide DNA diagnostic centers. RESULTS AND CONCLUSIONS: From 2012 to October 2016, available biochemical and clinical information of 3480 subjects with familial hypercholesterolemia identified according to the Dutch Lipid Clinic Network (DLCN) score were included in the database and genetic analysis was performed in 97.8% of subjects, with a mutation detection rate of 92.0% in patients with DLCN score 656. The establishment of the LIPIGEN network will have important effects on clinical management and it will improve the overall identification and treatment of primary dyslipidemias in Italy

Application of vibrational correlation formalism to internal conversion rate: Casestudy of Cu n (n = 3, 6, and 9) and H2/Cu3

International audienceThis work reports non-radiative internal conversion (IC) rate constants obtained for Cun with n = 3, 6,and 9 andH2 onCu3. TheTime-Dependent Density Functional Theory (TDDFT) methodwas employedwith three different functionals in order to investigate the electronic structures and the absorptionspectra. The performance of the generalized gradient approximation of Perdew, Burke and Ernzerhof(PBE) and the hybrid B3LYP and PBE0 exchange correlation functionals in combination with the SVPand the def2-TZVP basis setswas examined.TDDFTresults were used as input data to compute internalconversion rate constants. For this purpose, we have developed a program package. A descriptionof the theoretical background used in our numerical implementation and the program input file ispresented. In viewof future applications of this program package in photoinduced catalysis, we presentthe analysis of the IC rate processes for the photodissociation of H2 on Cu3. These results showedthe applicability of the method and the computational program to identify the vibrational modes intransition metal clusters giving rise to the largest IC rate constant due to their interactions with theexcited electronic states occurring in the hot-electron induced dissociation phenomena

Sodalite cages of EMT zeolite confined neutral molecular-like silver clusters

International audienceStable luminescent silver clusters in nanosized EMT zeolite suspension were prepared and directly observed with high-resolution transmission electron microscopy (HRTEM). The luminescence of the Ag clusters remains stable in time due to their stabilization within the sodalite cages (0.7 nm) of the EMT zeolite nanocrystals. In addition to the experimental results, the first principle Density Functional Theory (DFT) computations showed that hydrated neutral clusters up to octamer (Ag8) with a diameter of 0.47 nm were stabilized in the sodalite cages of the EMT zeolite, trough binding of silver atom(s) to the zeolite oxygen(s). The silver clusters exhibit molecular-like emission properties (lem = 395 nm and t1/2 ≤ 1 ns) that are in a good agreement with the HRTEM and DFT results. The stabilization of charge silver species in the form of weakly interacting dimer or trimer was observed too, which was based on the microsecond lifetime of the emission band measured at 545 nm. The high stability combined with the luminescence properties of silver clusters in the EMT zeolite nanocrystals will be of great advantage for applications such as bio imaging and bio sensing

Stability and Structures of Silver Subnanometer Clusters in EMT Zeolite with Maximum Aluminum Content

The stability of small silver clusters, Ag_<i>n</i> with <i>n</i> = 3, 4, 6, and 8, supported in a sodalite of EMT zeolite with a maximum possible aluminum content (Si/Al = 1) was studied with the density-functional-theory-based cluster approach. The results showed that various silver clusters, partially or completely reduced, can be stabilized in this zeolite with the maximum negative defects. Computed formation energies for two reduction reactions reveal that completely reduced Ag clusters can be stabilized through hydrogenation, giving some preference to the formation of hydrogenated Ag₆ species. The hydrogenated neutral Ag_<i>n</i>H_<i>m</i>/EMT clusters remain stable at <i>T</i> = 300 K, as obtained from the analysis of the Born–Oppenheimer molecular dynamics trajectories. Ion exchange of Na⁺ by Ag⁺ cations is obtained to be exothermic with energy gain of 0.5 eV per Ag cation. The formation of Ag–O ionic bonds, known to stabilize metal clusters in zeolitic frameworks, is found to be preponderant in the structures with fewer than six silver atoms, which leads to strong geometrical deformations especially for Ag₃ and Ag₄ species. The largest possibly stabilized in the sodalite completely reduced silver cluster is Ag₈. Partially reduced intact structures are obtained stable for silver clusters with <i>n</i> ≥ 4. Formation energies predict a coexistence of silver exchanged cations and partially reduced silver clusters with several oxidation states in the sodalite. The density of states spectra (DOSS) of the supported completely and partially reduced Ag₄ and Ag₈ clusters are very similar despite the different cluster size, topology, and reduction degrees. DOSS of the host zeolite did not undergo any changes due to the interaction with silver clusters

Computational Investigation on the Photophysical Properties of Halogenated Tetraphenyl BODIPY

The electronic structure, transition probabilities, and corresponding quantum yields of fluorescence in a family of dihalogen-tetraphenyl-aza-BODIPY were calculated at the Time-Dependent Density Functional and post-Hartree–Fock levels of theory. Excellent agreement between theoretical and experimental spectral-luminescent data was achieved with the HSE06 functional and the 6-311G* basis set. Because the fluorescence can be quenched through nonradiative intersystem spin crossing transitions from the lowest photoactive singlet state to triplet excited states, spin–orbit coupling matrix elements were calculated and applied along with Marcus–Levich–Jortner theory, leading to satisfactory agreement for the lifetimes in comparison with available experimental data. The anomalous dependence of the fluorescence efficiency on the atomic number of the halogen congeners was elucidated and shown to be due to an inversion between the fluorescent and the nearest triplet states in the iodinated compounds. The high rate of fluorescence quenching by intersystem crossings and the probability of collisions in a solvent between oxygen molecules and the molecules studied show that these molecules can provide efficient triplet sensitization. The most preferable sites for such interactions were predicted using electrostatic potential mapping at the extreme positive and negative charge points

Side Effects of Sulfur‐Based Geoengineering Due To Absorptivity of Sulfate Aerosols

Abstract Sulfur‐based stratospheric aerosol intervention (SAI) can cool the climate, but also heats the tropical lower stratosphere if done with injections at low latitudes. We explore the role of this heating in the climate response to SAI, by using mechanistic experiments that remove the effects of longwave absorption of sulfate aerosols above the tropopause. If longwave absorption by stratospheric aerosols is disabled, the heating of the tropical tropopause and most of the related side effects are strongly alleviated and the cooling per Tg‐S injected is 40% bigger. Such side‐effects include the poleward expansion of eddy‐driven jets, acceleration of the stratospheric residual circulation, and delay of Antarctic ozone recovery. Our results add to other recent findings on SAI side effects and demonstrate that SAI scenarios with low‐latitude injections of absorptive materials may result in atmospheric effects and regional climate changes that are comparable to those produced by the CO2 warming signal