Leo Klasinc

Photochemical formation and transport of ozone in Athens, Greece

Abstract An evaluation of the diurnal variation of the hourly ozone concentrations measured at five sites in Greater Athens from June until early September 1984 indicates that photosmog episodes in Greater Athens are associated with the sea breeze circulation. Due to local air circulation in the Athens basin, precursors of O3 are transported to and accumulated in the Saronikos Bay during the morning hours while the land breeze is blowing. At noon, when the sea breeze sets in, the O3 formed over the sea is brought back to the coast and to central Athens where it increases the local O3 concentration by a factor of 3–5 within a few hours. The O3 levels often remain high throughout the night. During the photochemical smog episodes, all of them accompanied by well-developed sea breezes, the U.S. Air Quality Standard of 120 ppb O3 was exceeded for 4–7 h day−1. Peak O3 concentrations up to nearly 200 ppb were recorded in the smog episodes. Relatively high O3 concentrations were measured on the island of Aegina. They tend to remain high during the night and can be attributed only to primary pollutant transport from Greater Athens advected by the land breeze. The O3 values obtained at Mount Immitos (1000 m above MSL) suggest that, first, the sea breeze inhibits the influence of vertical thermal convection up to heights above 600 m, and second, no O3 is noticeable from above the tropopause to ground level or from long-range transport.

Prediction of the Abiotic Degradability of Organic Compounds in the Troposphere

A statistically relevant correlation between the reaction rate coefficient, kOH, for the OH radical reaction with 161 organic compounds in the gas phase at 300 K, and the corresponding vertical ionisation energies Ei,v, reveals two classes of compounds: aromatics where −log(kOH/cm3s-1)≃3/2Ei,v(eV)−2 and aliphatics where −log(kOH/cm3s-1)≃4/5Ei,v(eV)+3. The prediction of the rate coefficient, kOH, for the reaction of OH with organic molecules from the above equations has a probability of about 90%. Assuming a global diurnal mean of the OH radical concentration of 5×105 cm3, the upper limit of the tropospheric half-life of organic compounds and their persistence can be estimated.

Preparative separations and racemizations of enantiomeric diaziridines

Abstract Preparative separations or enrichments of enantiomers of diaziridines 1 , 2 , and 5 were achieved by liquid chromatography on triacetylcellulose, (+)- 1 and (+)- 2 being isolated almost pure (Table 1). Enantiomeric purities were determined by 1 H NMR in the presence of the optically active auxiliary compound (+)-Eu(hfbc) 3 . The barriers to nitrogen inversion in 1 and 4 were determined and its lower limit in the nitrogen unsubstituted diaziridine 3 was estimated.

Photoelectron spectra of some halogenomethanes

The He I and He II photoelectron spectra of CBrCl3, CHBrCl2, CHBr2Cl, CH2BrCl, CHFCl2 and CHF2Cl have been recorded with low and high resolutions. Correlation with assignments for other halogenated methanes, comparison of He II/He I intensities and vibrational fine-structure analysis allowed all the systems with ionization energies up to 24 eV to be assigned.

Gas phase H/D exchange of sodiated amino acids: Why do we see zwitterions?

The gas-phase interaction of sodiated amino acids and sodiated amino acid methyl esters with various deuterium donors is investigated by combining results of H/D exchange reactions with those from density functional theory and molecular dynamics calculations. Discrepancy between experimentally and theoretically obtained structures for sodium cationized amino acids is explained by deuterium donor caused perturbation of the most stable amino acid conformation. Detailed study of H/D exchange mechanism on sodiated amino acids shows that the H/D exchange reaction is preceded by a multistep quasi-isoenergetic transition (perturbation) from a charge solvated to zwitterionic structure in the amino acid. Although the computation refers to the system AlaNa+ and D2O, these mechanisms apply to all amino acids, except those where a functional side-chain group takes part in the perturbation process. The suggested perturbation mechanism applies also for other deuterium donors such as CD3OD or even ND3 and indicates that a single water molecule suffices to convert the sodiated amino acid from charge solvated to zwitterionic form.

Photoelectron spectra, electronic structure and long-range electronic interaction in some steroids

Alicyclic molecular frameworks are useful for the study of electronic through-bond (TB) and through space (TS) interactions of functional groups over fixed distances and/or a specified number of C-C bonds. Steroids, being readily available, stable and stereochemically well-defined, are especially suited for such investigations. Indeed, their use in the study of the stereochemical aspects and the long-range effects of groups situated at specified distances from chemically reactive centers has been well documented over the last 20 years. Since steroids are compounds of considerable biological importance, their activity being dramatically dependent on construction, conformation and electronic structure, it is surprising that our knowledge of their electronic structure, whether by quantum chemistry or photoelectron (PE) spectroscopy, is so sparse. Having recorded the first PE spectra of steroids (refs. 1,2) we believe that such studies may resolve many problems concerning long-range intramolecular interaction since (i) PE spectroscopy is a gas phase method and its results pertain to the free molecule and (ii) steroids by virtue of their fixed geometry are unable to form intramolecular (head-to-tail) adducts in which both TB and TS effects might separately propagate. Indeed, one should expect the presence of TB interactions only. We report the PE spectra of several androstane derivatives and derive their electronic structure using empirical arguments and of quantum chemical, MNDO calculations. Emphasis is placed on the long range effects of a carbonyl group located at the biologically important 3-, 11- and 17- positions and the enhancement of these effects by interpolated, localized double bonds.The position and fine structure of the lowest energy PE bands and the shift of the a-onsets are the gauges used to estimate these effects. These long range effects seem to exert considerable influence on conformation, activity and, particularly , on fast intramolecular electron transfer (ET) such as has been observed recently in steroid solutions.

Chemistry of excited states. Part 13. Assignment of lowest π-ionizations in photoelectron spectra of thiophen, furan, and pyrrole

An assignment of the lowest π-ionizations(1b1π) in thiophen, furan, and pyrrole at 12.5, 15.3, and 12.9 eV, respectively, is achieved by a comparison of observed HeII/HeI intensity changes in the corresponding photoelectron spectra with calculated intensity trends for different possible assignments.

Boundary-Layer Ozone in Croatia

An analysis of ozone distribution in the atmosphericboundary layer based on monitoring data from two TORstations in Croatia is given. The levels were found tobe generally higher than expected for the continentalbackground. At the Puntijarka station, which can betaken as representative for the region, high valuesare mainly associated with transport from the west.The RBI station represents an urban site withoccasional photosmog situations. Short termmeasurements along the Adriatic coast have shown thatthere is a negative north to south gradient in ozoneconcentration as predicted by model calculations, butalso that some local photochemical production takesplace even at the remote Adriatic island far frompollution sources.

Eine Voraussagemethode zum abiotischen Abbauverhalten von organischen Chemikalien in der Umwelt

A statistically relevant correlation between the reaction rate coefficient for the OH radical reaction with organic compounds in the gas phase at 300 K, and the corresponding ionization energies allows a rapid prediction of the abiotic degradability of organic compounds in the troposphere. The tropospheric lifetime of the toxic methylisocyanate from the Bhopal accident is estimated to be about 5 days. Similarly, from a linear correlation of the reaction rate constant of ozone with aromatic compounds in water with the corresponding ionization potentials, the abiotic lifetime of these aromatic compounds during the final stage of drinking water purification by ozonation can be estimated, which allows a more economical use of ozone.

Ozone destruction on solid particles

Ozone (O3) is an important constituent of the Earth atmosphere, either stratosphere, where it has a beneficial role to protect Earths surface from harmful UV-B radiation, or troposphere where it is considered an air pollutant. We investigated the ozone destruction on solid particles of natural or anthropogenic origin as: silica-gel, pollen, coal fly ash, titanium dioxide with different specific surface (s) and sodium halides (NaCl, NaBr and NaI). The experiments were conducted in a fluidized bed reactor with elevated ambient concentrations of O3 (100 ppb) employed. The results indicate that the destruction of O3 depends upon: sample quantity (silica-gel with equal s), sample surface (TiO2 with different s) and chemical composition (coal fly ash comparative to wood ash). Interesting results were obtained with sodium halides: no effect on O3 concentrations was detected with NaCl, NaBr shows a certain destruction, while NaI removes completely O3 from the air stream. In the experiments with NaI doped NaCl, the destruction of O3 was dependent on NaI quantity.