Suchergebnisse

In this work, impact of aerosol solar extinction on the photochemistry over eastern Europe during the 2010 wildfires episode is discussed for the period from 5 to 12 August 2010, which coincides to the peak of fire activity. The methodology is based on an online coupling between the chemistry-transport model CHIMERE (extended by an aerosol optical module) and the radiative transfer code TUV. Results of simulations indicate an important influence of the aerosol solar extinction, in terms of intensity and spatial extent, with a reduction of the photolysis rates of NO2 and O-3 up to 50% (in daytime average) along the aerosol plume transport. At a regional scale, these changes in photolysis rates lead to a 3-15% increase in the NO2 daytime concentration and to an ozone reduction near the surface of 1-12 %. The ozone reduction is shown to occur over the entire boundary layer, where aerosols are located. Also, the total aerosol mass concentration (PM10) is shown to be decreased by 1-2 %, on average during the studied period, caused by a reduced formation of secondary aerosols such as sulfates and secondary organics (4-10 %) when aerosol impact on photolysis rates is included. In terms of model performance, comparisons of simulations with air quality measurements at Moscow indicate that an explicit representation of aerosols interaction with photolysis rates tend to improve the estimation of the near-surface concentration of ozone and nitrogen dioxide as well as the formation of inorganic aerosol species such as ammonium, nitrates and sulfates.

8 pags., 5 figs., 2 tabs. ; Mercury (Hg), a global contaminant, is emitted mainly in its elemental form Hgto the atmosphere where it is oxidized to reactive Hgcompounds, which efficiently deposit to surface ecosystems. Therefore, the chemical cycling between the elemental and oxidized Hg forms in the atmosphere determines the scale and geographical pattern of global Hg deposition. Recent advances in the photochemistry of gas-phase oxidized Hgand Hgspecies postulate their photodissociation back to Hgas a crucial step in the atmospheric Hg redox cycle. However, the significance of these photodissociation mechanisms on atmospheric Hg chemistry, lifetime, and surface deposition remains uncertain. Here we implement a comprehensive and quantitative mechanism of the photochemical and thermal atmospheric reactions between Hg, Hg, and Hgspecies in a global model and evaluate the results against atmospheric Hg observations. We find that the photochemistry of Hgand Hgleads to insufficient Hg oxidation globally. The combined efficient photoreduction of Hgand Hgto Hgcompetes with thermal oxidation of Hg, resulting in a large model overestimation of 99% of measured Hgand underestimation of 51% of oxidized Hg and ∼66% of Hgwet deposition. This in turn leads to a significant increase in the calculated global atmospheric Hg lifetime of 20 mo, which is unrealistically longer than the 3-6-mo range based on observed atmospheric Hg variability. These results show that the Hgand Hgphotoreduction processes largely offset the efficiency of bromine-initiated Hgoxidation and reveal missing Hg oxidation processes in the troposphere. ; This study has received funding from the European Research Council Executive Agency under the European Union's Horizon 2020 Research and Innovation programme (Project ERC-2016- COG 726349 CLIMAHAL) and the Spanish Ministerio de Economía y Competitividad (MINECO) /Fondo Europeo de Desarrollo Regional (FEDER) (Projects CTQ2017-87054-C2-2-P, RYC-2015-19234, and CEX2019-000919-M). This work was supported by the Consejo Superior de Investigaciones Científicas (CSIC) Spain. A.F.-M. acknowledges the Generalitat Valenciana and the European Social Fund (Contract APOSTD/2019/149 and Project GV/2020/ 226) for the financial support. J.C.-G. acknowledges the Universitat de València for his Masters Scholarship. M.J. acknowledges funding by the Swiss National Science Foundation (Grant PZ00P2_174101). The ETMEP measurements as well as ground-based measurements of the GMOS network were funded by the EU FP7-ENV-2010 project (GMOS, Grant Agreement 265113). J.S.F. acknowledges the H2020 ERA-PLANET (689443) Integrated Global Observing Systems for Persistent Pollutants (iGOSP) and Integrative and Comprehensive Understanding on Polar Environments (iCUPE) programs

[EN] The photophysics and photochemistry of the beta-lapachone derived diphenyldihydrodioxin 3 were investigated using steady-state and time resolved techniques. Laser excitation of 3 leads to the formation of its cation radical 4 (absorption maxima at 410 and 450 nm and a lifetime of 10 mu s), which was confirmed by its thermal generation employing tris(2,4-dibromophenyl)-aminium hexachloroantimonate (BAHA) as the electron acceptor. The cation radical 4 was also formed via the triplet excited state of 3 through a triplet sensitized process using benzophenone (E-T = 69 kcal mol(-1)) as the sensitizer. ; Financial support by the Spanish Government (grant CTQ2012-32621) is gratefully acknowledged. We thank Prof. Julia Pérez-Prieto for making available the laser flash photolysis facilities at the University of Valencia. BB thanks Coordena- ção de Aperfeiçoamento do Pessoal do Ensino Superior (CAPES-Brazil) for a graduate fellowship. JCN-F thanks Generalitàt Valenciana for a Visiting Professor fellowship. ; Netto Ferreira, JC.; Lhiaubet ., VL.; Bernades, B.; Ferreira, ABB.; Miranda Alonso, MÁ. (2014). Photophysics and photochemistry of the beta-lapachone derived diphenyldihydrodioxin: generation and characterization of its cation radical. Photochemical & Photobiological Sciences. 13(12):1655-1660. https://doi.org/10.1039/C4PP00231H ; S ; 1655 ; 1660 ; 13 ; 12

"Monsanto Research Corporation a subsidiary of Monsanto Company"--Cover. ; "Mound Laboratory, Miamisburg, Ohio, operated for United States Atomic Energy Commission, U.S. Government Contract Number AT 33-1-GEN-53." ; "Date: December 11, 1964 ; Issued: March 10, 1965." ; "MLM-1214 ; TID-4500 (35th Ed.) ; UC-22 Isotope Separation." ; Includes bibliographical references (p. 11). ; U.S. Atomic Energy Commission Contract ; Mode of access: Internet.

Clean use of photons from light to activate chemical reactions offers many possibilities in different fields, from chemistry and biology to materials science and medicine. This review article describes the advances carried out in last decades toward the phototriggered synthesis of single-chain polymer nanoparticles (SCNPs) as soft nanomaterials with promising applications in enzyme-mimicking catalysis and nanomedicine, among other different uses. First, wesummarize some different strategies developed to synthesize SCNPs based on photoactivated intrachain homocoupling, phototriggered intrachain heterocoupling and photogenerated collapse induced by an external cross-linker. Next, we comprehensively review the emergent topic of photoactivated multifolding applied to SCNP construction. Finally, we conclude by summarizing recent strategies towards phototriggered disassembly of SCNPs. ; This research was funded by Gipuzkoako Foru Aldundia -Programa Red Gipuzkoana de Ciencia, Tecnología e Innovación 2019-, grant number 2019-CIEN-000050-01; Basque Government, grant number IT-1175-19; and MCIU/AEI/FEDER, UE, grant number PGC2018-094548-B-I00.