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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 5519-5526 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The energy distribution of the NH(A) radicals generated by two photons in the ArF laser (193.3 nm) photolysis of NH3 was studied in detail using high spectral resolution. The different spin components were found to be statistically populated. For the likely photodissociation process NH3+2hν(ArF)→NH(A, v'=0, N')+H+H, the rotational population matches the prior distribution for fragmentation into two rather than three fragments indicating that both atomic fragments are not equivalent with respect to the dissociation process. It therefore seems to be likely that first an excited NH2 intermediate is formed which subsequently is photolyzed to yield NH(A). From energy conservation, the upper limit for the heat of formation of NH(X 3Σ−) is deduced to be ΔH0f0 (NH)≤367 kJ mol−1. The quantum yield for the generation of NH(A) was estimated to be φ[NH(A)]≈5×10−4. About 5.2% of the excited radicals were found to be produced in v'=1. In addition, a process involving the absorption of at least three photons was observed. About 1% of the excited radicals are formed this way with a rotational temperature of 2500 K for v'=0. These radicals are generated with such a short delay that reactions of ions appear to be involved in their formation.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of atmospheric chemistry 15 (1992), S. 269-282 
    ISSN: 1573-0662
    Keywords: Photolysis frequency ; J(NO2) ; global radiation ; aerosol ; meridional cross section ; marine atmosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Using a filter radiometer, the meridional profile of the NO2 photolysis frequency, J(NO2), was measured between 50° N and 30° S during the cruise ANTVII/1 September/October 1988 of the research vessel Polarstern on the Atlantic Ocean. Simultaneously, global broadband irradiance and acrosol were monitored. Clean marine background air with low aerosol loads (b sp=(1–2)×10-5 m-1) was encountered at the latitudes 25° N–30° N and 18° S–27° S, respectively. Under these conditions and an almost cloudless sky J(NO2) reached 7.3×10-3 s-1 (2π sr) for a zenith angle of 30°. Between 30° N and 30° S, the latitudinal variation of the J(NO2) noontime maxima was less than ± 10%, while the mean value at noon was 7.8×10-3 s-1. For the set of all data between 50° N and 30° S, a nearly linear correlation of J(NO2) vs. global broadland irradiance was found. The slope of (8.24±0.03)×10-5 s-1/mW cm-2 agrees within 10% with observations in Jülich (51° N, 6.2° E).
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-0662
    Keywords: Photolysis frequency ; J(O1D), O3, H2O ; OH production rate ; meridional cross-section ; marine atmosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The latitudinal variation of the photolysis frequency of ozone to O(1D) atoms, J(O1D), was measured using a filter radiometer during the cruise ANT VII/1 of the research vessel Polarstern in September/October 1988. The J(O1D) noon values exhibited a maximum of 3.6×10-5 s-1 (2π sr) at the equator and decreased strongly towards higher latitudes. J(O1D) reached highest values for clean marine background air with low aerosol load and almost cloudless sky. The J(O1D) data, measured under these conditions and a temperature of 295 K, can be expressed by: % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOsaiaacI% cacaqGpbWaaWbaaSqabeaaiiaacqWF8baFaaGccaqGebGaaeykaiaa% bccacqWF9aqpcaqGGaGaaeyzaiaabIhacaqGWbGaaeiiaiaabUhacq% GHsislcaaI4aGaaiOlaiaaicdacaaIYaGaeyOeI0IaaGioaiaac6ca% caaI4aGaaiiEaiaaigdacaaIWaWaaWbaaSqabeaacqGHsislcaaIZa% aaaOGaaeiiaiaabIhacaqGGaGaam4uaiabgUcaRiaaiodacaGGUaGa% aGinaiaacIhacaaIXaGaaGimamaaCaaaleqabaGaeyOeI0IaaGOnaa% aakiaadofadaahaaWcbeqaaiaaikdaaaGccaGG9bGaaeikaiaaboha% daahaaWcbeqaaiabgkHiTiaaigdaaaGccaGGPaaaaa!5EE9!\[J({\text{O}}^| {\text{D) }} = {\text{ exp \{ }} - 8.02 - 8.8x10^{ - 3} {\text{ x }}S + 3.4x10^{ - 6} S^2 \} {\text{(s}}^{ - 1} )\] where S represents the product of the overhead ozone column (DU) and the secant of the solar zenith angle. The meridional profile of the primary OH radical production rate P(OH) was calculated from the J(O1D) measurements and simultaneously recorded O3 and H2O mixing ratios. While the latitudinal distribution of J(O1D) and water vapour was nearly symmetric to the equator, high tropospheric ozone levels up to 40 ppb were observed in the Southern Hemisphere, SH, resulting in higher P(OH) in the SH.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of atmospheric chemistry 31 (1998), S. 161-180 
    ISSN: 1573-0662
    Keywords: photolysis ; actinic flux ; UV radiation ; spectroradiometer ; radicals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract A calibrated spectroradiometer was used for the measurement of spectra of the absolute actinic flux Fλ during the POPCORN field campaign in Pennewitt (53.8° N, 11.7° E, sea level) in August 1994. The obtained set of actinic flux spectra was used to determine the photolysis frequencies J(O1D), J(NO2), J(HCHO), J(H2O2), J(HONO), and J(CH3CHO), using molecular photodissociation data from literature. The accuracy of the actinic flux measurement was about ±5%. The accuracy of the photolysis frequency determination is limited by the uncertainties of the molecular absorption cross section and quantum yield data. A good agreement within the experimental uncertainties was found in comparison with measurements of J(O1D) and J(NO2) by filterradiometer which were calibrated absolutely against chemical actinometer. A comparison of this work's photolysis frequency measurements at 40° solar zenith angle with respective measured and modeled data from the literature also shows good agreement for most of the processes considered in this work. However, in the case of J(NO2) data reported in the literature as a function of solar zenith angle differences up to a factor of 1.6 with respect to this work's J(NO2) data are observed. Since this is far beyond the estimated experimental uncertainties, other atmospheric variables, such as aerosols, seem to affect J(NO2) to an extent that is underestimated by now and make indirect comparisons of J(NO2) measurements difficult.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-0662
    Keywords: OH instrument ; laser-induced fluorescence ; OH measurements ; photochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Tropospheric hydroxyl radical (OH) concentrations were measured by laser-induced fluorescence (LIF) during the POPCORN field campaign in August 1994 at a rural site in the North East of Germany. Ambient air spectra were recorded by tuning the laser wavelength over a spectral region covering the Q11(3), Q21(3), and P11(1) rotational transitions of the (0-0) band in the A-X system of OH around 308 nm. The observed spectra clearly identify the OH radical in the atmosphere. Besides the OH absorption lines there was no sign of any other narrow-band spectral structure nearby demonstrating the high specificity of the method. For OH measurements with a typical time resolution of 60–100 seconds per data point the laser wavelength was tuned repetitively over small spectral intervals covering the peak position of the P11(1) OH-line and background positions. A total of 2300 measurements were recorded including diurnal cycles of OH with more than 300 data points. The OH as well as the LIF background signal data will be presented. In a first analysis the background signal will be characterized and the correlation between OH and the ozone photolysis frequency will be derived.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-0662
    Keywords: OH intercomparison ; laser absorption spectroscopy ; DOAS ; laser induced fluorescence ; LIF ; troposphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract In-situ OH measurements by laser-induced fluorescence (LIF) spectroscopy and folded long-path differential optical absorption spectroscopy (DOAS) were carried out in a rural environment in North-East Germany as part of the field experiment POPCORN in August 1994. The large set of OH data obtained allowed an intercomparison of both techniques based on relative diurnal profiles and simultaneously measured absolute concentrations. Most of the time the two OH instruments encountered the same air and agreed well in the measured relative diurnal variations. Only on a few occasions the measurements significantly disagreed due to a perturbation of the DOAS measurements by a local OH source in the north-western wind sector. Excluding data from this wind direction, the statistical analysis of 137 data pairs yields a correlation coefficient of r = 0.90 and a weighted linear fit with a slope of 1.09 ± 0.12. The correlations are carefully analyzed. The comparison of both instruments is discussed in the light of newly published effective absorption cross-sections for H2O and O2 that affect the calibration of LIF.
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 2019-07-16
    Description: Das mehrstufige Grossexperiment TRACKS (Transporte und chemische Umsetzungen in konvektiven Systemen) der Helmholtzzentrendient dem Ziel, konvektive Systeme von der kleinräumigen Turbulenz bis zur hochreichenden Wolkenkonvektion in Gewitterkomplexen undFronten hinsichtlich ihrer steuernden physikalischen und chemischen Prozesse, ihrer Transporteigenschaften für Energie, Wasser undLuftschadstoffe und ihrer Klimawirkungen in verschiedenen Klimazonen experimentell zu erforschen. In einem Zeitraum von 6 bis 8 Jahrenwerden konvektive Systeme in Nordeuropa, Mitteleuropa und den Tropen untersucht. Das Vorhaben besitzt besondere gesellschaftlicheRelevanz, da der Vertikalaustausch, die Ferntransporte und die chemischen Umsetzungen von atmosphärischen Spurenstoffen klima- undumweltrelevant sind. Sie bewirken globale Umverteilungen von Spurenstoffen und modifizieren den Treibhauseffekt. Sie prägen inbesonderem Maße die Verteilung von Luftschadstoffen. Absehbare Ergebnisse sind gesicherte Aussagen über den Eintrag vonSpurenstoffen in die Atmosphäre vom Boden bis in die Stratosphäre, die Wirksamkeit des Vertikaltransports durch konvektive Systeme,insbesondere für europäische Ballungszonen, Bilanzierungen der überregionalen und vertikalen Verteilung von Wasserdampf undSpurengasen, die im Wesentlichen an der Erdoberfläche emittiert werden, und verbesserte Darstellungen der konvektiven Transporte undphysikalisch-chemischen Prozesse in Modellen zur Schadstoffausbreitung, Wetter- und Klimavorhersage.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Book , peerRev
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  • 8
    Publication Date: 2018-07-20
    Description: Air pollution is growing fastest in monsoon-affected South Asia. During the dry winter monsoon, the fumes disperse toward the Indian Ocean, creating a vast pollution haze, but their fate during the wet summer monsoon has been unclear. We performed atmospheric chemistry measurements by aircraft in the Oxidation Mechanism Observations campaign, sampling the summer monsoon outflow in the upper troposphere between the Mediterranean and the Indian Ocean. The measurements, supported by model calculations, show that the monsoon sustains a remarkably efficient cleansing mechanism by which contaminants are rapidly oxidized and deposited to Earth’s surface. However, some pollutants are lofted above the monsoon clouds and chemically processed in a reactive reservoir before being redistributed globally, including to the stratosphere.
    Keywords: Geochemistry, Geophysics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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