Michal Střižík

Dispersion of Light and Heavy Pollutants in Urban Scale Models: CO2 Laser Photoacoustic Studies

The distribution of pollutants in two urban scale models (point emission source and street canyon with extensive transport) was investigated by means of CO2 laser photoacoustic spectroscopy in the region of the atmospheric window (9–10 μm). The experimental results of physical modeling are in a good agreement with the numerical calculations performed in the frame of computational fluid dynamic (CFD) modeling. Methanol, ethanol, and ozone (examples of light pollutants), as well as sulfur hexafluoride and 1,2 dichlorethane (examples of heavy pollutants), were selected on the basis of their high resolution spectra acquired by Fourier transform and laser diode spectroscopy.

First analysis of the high resolution FTIR spectrum of the ν2 band of the FCO2 radical at 970.2 cm−1

The infrared spectrum of the fluorocarboxyl radical, FCO2, was recorded at high resolution (0.0035 cm−1) in the 600–1400 cm−1 region on a Bruker IFS 120 HR Fourier transform spectrometer of the University of Wuppertal. The analysis of the A-type ν2 band of FCO2 (CF stretching mode) centred at 970.208 cm−1 was performed making use of the ground state parameters achieved by [L. Kolesniková, J. Varga, H. Beckers, M. Šimečková, Z. Zelinger, L. Nová Stříteská, P. Kania, H. Willner, and Š. Urban, J. Chem. Phys. 128, 224302/1 (2008)]. For the FCO2 radical, the ν2 transitions are, in principle, split into two spin–rotation subcomponents corresponding to J = N ±1/2. However the spin–rotation parameters in the 21 vibrational state have values similar to those of the ground state, and spin–rotation doublings are observable only for the weaker transitions involving medium Ka or Kc values in the P and R branches. The ν2 fundamental band is weakly perturbed by the 2ν5 dark overtone band at 965.4 cm−1 and the 21 and 52 energy levels of FCO2 are coupled through Fermi type resonances. The final energy level calculation was performed accounting both for the spin–rotation interaction within the 21 and 52 vibrational states, and the 21 ⇔ 52 Fermi-type resonances.

Ablation of ionic crystals induced by capillary-discharge XUV laser

Single crystals of two fluorides (LiF and CaF2) and a tungstate (PbWO4) were irradiated by nanosecond pulses of 46.9- nm radiation provided by 10-Hz capillary-discharge Ne-like Ar laser (CDL). The damage threshold was determined in LiF using the CDL beam focused by a Sc/Si multilayer-coated spherical mirror. Irradiated samples have been investigated by Nomarski (DIC - Differential Interference Contrast) microscopy and optical (WLI - white light intereferometry) profiler. After an exposure by a certain number of CDL pulses, an ablation rate can be calculated from WLI measured depth of the crater created by the XUV ablation. Potential use of XUV ablation of ionic crystals in pulsed laser deposition (PLD) of thin layers of such a particular material, which is difficult to ablate by conventional UV-Vis- NIR lasers, is discussed in this contribution.

CFD modelling for atmospheric pollutants/aerosols studies within the complex terrains of urban areas and industrial sites

Computational fluid dynamic (CFD) modelling of pollution dispersion and chemical conversion to aerosol particles in the atmospheric boundary layer (ABL) has been studied. The investigation focused on the numerical modelling above complex orographic terrains of urban areas and industrial sites including the dispersion of toxic substances in the air as a result of accidents. A finite-rate model of chemical reactions, including the turbulence chemistry for modelling the reaction between nitric acid and ammonia, has been applied. As supporting experiments, online monitoring of the spatial distribution of pollutants and aerosols has been performed above real complex areas. Minimal detectable concentrations 8 μg m–3 (SO2), 20 μg m–3 (NO2), 2 μg m–3 (O3) and minimal detectable absorptivity 5 × 10–7 cm–1 (aerosols) have been reached.