Tomislav Cvitaš

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.

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.

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.

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.

Photoelectron spectrum of tetravinylstannane, Sn(CHCH2)4

Abstract The HeI and HeII photoelectron spectra of tetravinylstannane are reported and assigned on the basis of comparison with the spectra of other Group IVB tetravinyl derivativ and by correlation of the electronic structures of ethene and stannane.

Photoelectron spectra of lodobenzenes

The photoelectron spectra of iodobenzene and 1,2-, 1,3-. and 1,4-di-iodobenzene have been recorded by using HeI excitation. The electronic structure of these compounds is discussed in terms of a simple model of interaction between known orbitals of the composite parts, i.e. the molecular orbitals of benzene and the 5p atomic orbitals of iodine, taking their energy and symmetry but no spin–orbit coupling into account. The assignment is simplified by the characteristic shapes of several systems, which holds especially for the lone-pair electrons on iodine. Orbital sequences are given down to ionisation energies of 17 eV. Assignments are supported by comparison with the photoelectron spectra of 1,2,3,4-tetrafluoro-5,6-di-iodo- and 1,2,4,5-tetrafluoro-3,6-di-iodo-benzene.

High resolution photoelectron spectrum of hydrazoic acid

The He(II) photoelectron spectrum of hydrazoic acid has been recorded showing six systems which were correlated with the electronic structure of the isoelectronic N2O molecule. The high resolution He(I) spectrum of HN3 showed in the first system bands having perpendicular-type rotational structure, thus proving that the molecular ion is non-linear in its ground state. The vibrational wave-numbers of the ions HN+3 and DN+3 in the first three systems are compared with previous results.

Gas phase reaction rate measurements in Fourier transform mass spectrometry.

Determination of the concentration of neutral polycyclic aromatic hydrocarbon molecules in the mass spectrometer for reaction rate measurement is investigated. Copyright 1999 John Wiley & Sons, Ltd.

Photoelectron spectra of bromo- and iodo-thiophens

The photoelectron spectra of bromo- and iodo-thiophens with the halogen(s) in the 2-,3-. 2,5-, 3,4-, 2,3,5-, and 2,3,4,5-positions, have been recorded with HeI radiation, and the ionisation energies have been assigned down to 13 eV. The spectra were analysed on the basis of qualitative molecular orbital description, by mutual comparison and comparison with the spectra of bromo- and iodo-benzenes. Interactions between halogen Ione-pair electrons are discussed.