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121.
T. Röckmann J. Kaiser C. A. M. Brenninkmeijer W. A. Brand R. Borchers J. N. Crowley 《Isotopes in environmental and health studies》2013,49(2):91-95
Abstract The position dependent 15N fractionation of nitrous oxide (N2O), which cannot be obtained from mass spectrometric analysis on molecular N2O itself, can be determined with high precision using isotope ratio mass spectrometry on the NO+ fragment that is formed on electron impact in the source of an isotope ratio mass spectrometer. Laboratory UV photolysis experiments show that strong position dependent 15N fractionations occur in the photolysis of N2O in the stratosphere, its major atmospheric sink. Measurements on the isotopic composition of stratospheric N2O indeed confirm the presence of strong isotope enrichments, in particular the difference in the fractionation constants for 15N14NO and 14N15NO. The absolute magnitudes of the fractionation constants found in the stratosphere are much smaller, however, than those found in the lab experiments, demonstrating the importance of dynamical and also additional chemical processes like the reaction of N2O with O(1D). 相似文献
122.
Carbonyl peroxy radicals (RC(O)O2) are the ubiquitous radical intermediates in the atmospheric oxidation of volatile organic compounds. In this work, theoretical studies are carried out to explore the role of the unimolecular H-migration in the carbonyl peroxy radicals by using quantum chemistry and kinetics calculations. The results showed that H-migration could be significant in the atmosphere at least in CH3CH2CH2C(O)O2 and (CH3)2CHCH2C(O)O2 with rates of ∽0.012 and ∽0.58 s?1 at 298 K. Subsequent reactions of CH3CHCH2C(O)OOH would lead to the products with multi-functional groups, which might affect the aerosol formation process; while (CH3)2CCH2C(O)OOH would transform to formaldehyde and acetone in a few steps. These processes would be important for the atmospheric modelling of volatileorganic compounds under low-NOx conditions. 相似文献
123.
N. Jacquinet-Husson N.A. Scott L. Crépeau V. Capelle A. Coustenis N. Poulet-Crovisier M. Birk C. Camy-Peyret K. Chance C. Clerbaux P.F. Coheur L. Daumont G. Di Lonardo A. Goldman M. Hess D. Jacquemart P. Köpke S. Massie V. Nemtchinov D. Newnham V.I. Perevalov L. Régalia-Jarlot A. Rublev L. Schult S.A. Tashkun R.A. Toth J. Vander Auwera G. Wagner 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(6):1043-1059
The development of Gestion et Etude des Informations Spectroscopiques Atmosphériques (GEISA: Management and Study of Spectroscopic Information) was started over three decades at Laboratoire de Météorologie Dynamique (LMD) in France. GEISA is a computer accessible spectroscopic database, designed to facilitate accurate forward radiative transfer calculations using a line-by-line and layer-by-layer approach. More than 350 users have been registered for on-line use of the GEISA facilities. The current 2003 edition of GEISA (GEISA-03) is a system comprising three independent sub-databases devoted respectively to: line transition parameters, infrared and ultraviolet/visible absorption cross-sections, microphysical and optical properties of atmospheric aerosols.Currently, GEISA is involved in activities related to the assessment of the capabilities of IASI (Infrared Atmospheric Sounding Interferometer on board of the METOP European satellite) through the GEISA/IASI database derived from GEISA.The GEISA-03 content is presented, placing emphasis on molecular species of interest for Earth and planetary atmosphere studies, with details on the updated 2008 archive underway. A critical assessment on the needs, in terms of molecular parameters archive, related with recent satellite astrophysical missions is made. Detailed information on free on-line GEISA and GEISA/IASI access is given at http://ara.lmd.polytechnique.fr and http://ether.ipsl.jussieu.fr. 相似文献
124.
Arturo Quirantes Francisco J. Olmo Hassan Lyamani Lucas Alados-Arboledas 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(8):1496-1503
Total aerosol scattering and backscattering atmospheric values are typically obtained with an integrating nephelometer. Due to design limitations, measurements do not cover the full (0°–180°) angular range, and correction factors are necessary. The effect of angle cutoff is examined for a number of particle size distributions and refractive indices. Scattering data for sub-micron particles can be corrected by the use of a modified Anderson approximation, while data for larger particle distributions can be approximated by a function of the effective size parameter. Correction factors for the hemispheric backscatter ratio are found to be small if nonsphericity is assumed. Such approximations will help more accurate corrections for angle range, particularly at large size parameter values. 相似文献
125.
We report on the development of a laser source in the mid-infrared spectral region based on difference-frequency generation (DFG) in a periodically poled LiNbO3 (PPLN) crystal. Continuously tunable coherent radiation from 2.75 to 4.78 μm was produced by optical parametric interaction between a diode-pumped monolithic continuous-wave (CW) Nd:YAG laser operating at 1.064 μm and a CW Ti:Sapphire laser tunable from 767 to 871 nm. Temperature-dependent quasi-phase-matched DFG wavelength acceptance bandwidth was studied and characterized. An empiric formula is given to estimate the phase-matched wavelength acceptance bandwidth as a function of the crystal temperature at Λ = 22.5 μm. A large frequency scan of 128 cm−1 (about 78 cm−1 above 1 μW) near 4.2 μm was achieved. The whole absorption spectrum of the P and R branches of the ν3 band of atmospheric carbon dioxide has been recorded with a single phase-matched frequency scan. 相似文献
126.
Spectral characteristics of partially coherent flat-topped (PCFT) beams propagated in a turbulent atmosphere are investigated and an analytical formula for the spectrum S(ω) is derived. It is shown that, if the scaling law is valid, the normalized spectrum S(ω) of PCFT beams propagating through turbulent atmosphere is the same as the normalized source spectrum S(0)(ω), this similarity is valid for any arbitrary order of the circular flat-topped “N”. It is proved that if the scaling law is not valid, S(ω) of PCFT is different from S(0)(ω). Also spectral behavior of PCFT beams in free space and turbulence media is investigated in detail. 相似文献
127.
M.H. Mahdieh 《Optics Communications》2008,281(13):3395-3402
In this paper, propagation of a Gaussian laser beam through turbulent atmosphere is evaluated numerically. The beam quality factor for the propagated beam has been estimated for different turbulent conditions that are characterized by parameter Cn. The calculations show that the beam quality can be affected dramatically by atmospheric turbulence and the laser beam size and wavelength have major role in the results. Furthermore, the propagation of laser beam in longer distance results in more spatial perturbation of the beam. The results of these calculations and evaluation of beam quality factor M2 can be used for estimating the refractive index structure parameter (or atmosphere turbulent parameter) Cn. 相似文献
128.
Spreading of spatially partially coherent polychromatic beams in atmospheric turbulence 总被引:1,自引:0,他引:1
Taking the polychromatic Gaussian Schell-model (GSM) beam as a typical example of spatially partially coherent polychromatic beams, the spreading of polychromatic GSM beams in atmospheric turbulence is studied. The mean-squared width of polychromatic GSM beams in turbulence is derived by using the effective source and the strong fluctuation models. It is shown that the same result is obtained using both the models. The diffraction, atmospheric turbulence and beam polychroism result in a spreading of polychromatic GSM beams. If the scaling law fails, the spreading of polychromatic GSM beams increases with increasing bandwidth Γ, but the influence of Γ on the spreading of polychromatic GSM beams becomes small as the structure constant Cn2 of the refractive index and spatial correlation parameter α increase. The spreading of polychromatic GSM beams increases as Cn2 increases and α decreases. Spatially partially coherent polychromatic beams are less sensitive to the effects of atmospheric turbulence than spatially fully coherent polychromatic beams. 相似文献
129.
Nowadays, many ultrasonic sensory systems are being developed to operate outdoors, where they are finding a variety of applications, such as local positioning, vehicle navigation or obstacle detection. To assure the reliable operation of these systems under any meteorological condition, it is necessary to achieve a thorough comprehension of the effects that the different atmospheric phenomena can have on the propagation of these acoustic waves. This paper deals with one of these phenomena, atmospheric refraction, and its influence on the performance of an ultrasonic system whose signals are detected by matched filtering. 相似文献
130.