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  • 1
    ISSN: 0022-4073
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0992-7689
    Keywords: Atmospheric composition and structure (pollution – urban and regional; troposphere – composition and chemistry) ; Meteorology and atmospheric dynamics (mesoscale meteorology)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The “Étude et Simulation de la QUalité de l’air en Ile de France” (ESQUIF) project is the first integrated project dedicated to the study of the processes leading to air pollution events over the Paris area. The project was carried out over two years (summer 1998 to winter 2000) to document all types of meteorological conditions favourable to air quality degradation, and in particular to photo oxydant formation. The goals of ESQUIF are (1) to improve our understanding of the relevant chemical and dynamical processes and, in turn, improve their parametrizations in numerical models, and (2) to improve and validate existing models dedicated to pollution analysis, scenarios and/or forecasting, by establishing a comprehensive and thorough database. We present the rationale of the ESQUIF project and we describe the experimental set-up. We also report on the first experiments which took place during the summer of 1998 involving surface networks, and remote sensing instruments as well as several aircraft. Focusing on three days of August 1998, the relative contributions of long-range transported and locally-produced ozone to the elevated ozone concentrations observed during this period are discussed and chemistry-transport model preliminary results on this period are compared to measurements.
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  • 3
    ISSN: 0047-2670
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Photochemistry 6 (1976), S. 241-252 
    ISSN: 0047-2670
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-0662
    Keywords: Vertical ozone profiles ; Tropospheric Ozone Research Project ; Brewer-Mast sondes ; ground-based UV-DIAL
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract An intercomparison campaign was conducted at the Observatoire de Haute Provence (OHP) in Southern France in September 1989 in order to compare the three instruments used for vertical tropospheric ozone profiling in the European TOR (Tropospheric Ozone Research Project) network: balloon borne ECC and Brewer-Mast sondes and a ground based UV-DIAL (DifferentialAbsorptionLidar). Additionally, a stratospheric lidar system and the Dobson spectrophotometer of the OHP were operated. Seven simultaneously measured vertical ozone profiles gave evidence for systematic differences of 15% between both types of electrochemical sondes in the troposphere, the Brewer-Mast sondes reading the smaller ozone values. These differences might be explained on the one hand by a possible contamination of the ozone sensor with reducing substances, causing a negative bias mainly for Brewer-Mast sondes and, on the other hand, by the evolution of the sonde background current during the flight, causing a positive bias for ECC sondes and a negative bias for Brewer-Mast sondes. The tropospheric lidar system, measuring the vertical ozone distribution between 6 and 12–15 km, showed ozone concentrations intermediate between the sonde results. This is in good agreement with its estimated systematic error of better than 7% in the upper troposphere. In the stratosphere, the differences between electrochemical sondes and the lidar are between 5 and 10% before the normalisation with the total ozone values measured by the Dobson spectrophotometer, and always below 5% after. While the Dobson normalisation thus corrects rather well the stratospheric part of the sonde profile, it only partially reduces errors occurring in the troposphere.
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  • 6
    ISSN: 1573-0662
    Keywords: O3 ; Ox ; boundary layer ; lower troposphere ; Europe ; distribution ; seasonal variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Surface ozone data from 25 Europeanlow-altitude sites and mountain sites located between79°N and 28°N were studied. The analysiscovered the time period March 1989–February 1993.Average summer and winter O3 concentrations inthe boundary layer over the continent gave rise togradients that were strongest in the north-west tosouth-east direction and west-east direction, respectively. WintertimeO3 ranged from 19 to 27 ppbover the continent, compared to about 32 ppb at thewestern border, while for summer the continentalO3 values ranged between 39 and 56 ppb and theoceanic mixing ratios were around 37 ppb. In the lowerfree troposphere average wintertime O3 mixingratios were around 38 ppb, with only an 8 ppbdifference between 28°N and 79°N. For summerthe average O3 levels decreased from about 55 ppbover Central Europe to 32 ppb at 79°N. Inaddition, O3 and Ox(= O3 + NO2)in polluted and clean air were compared. Theamplitudes of the seasonal ozone variations increasedin the north-west to south-east direction, while thetime of the annual maximum was shifted from spring (atthe northerly sites) to late summer (at sites inAustria and Hungary), which reflected the contributionof photochemical ozone production in the lower partsof the troposphere.
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  • 7
    ISSN: 1573-0662
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-0662
    Keywords: nonmethane hydrocarbons ; troposphere ; ambient hydrocarbon measurements ; seasonal variation ; biogenic emissions of light olefins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Long-term measurements of light hydrocarbons(C2–C5 HC‘s) were performed in the courseof the EUROTRAC sub-project TOR (Tropospheric Ozone Research) in thesouthern part of the Black Forest in southwest Germany. The measurementscover a time period of five years (January 1989–January 1994) and theair samples were analyzed onsite by an automated GC-system. Pronouncedannual cycles with maxima in late winter and minima in late summer wereobserved in the case of the slowly reacting hydrocarbons ethane, propane andacetylene, reflecting the fact that the seasonal variation of these speciesis photochemically driven. For the shorter lived compounds the seasonalvariations are considerably weaker, connected with a stronger scatter of theindividual measurements, which is caused by different distances to theirmain sources for different wind vectors as well as by varying sourcestrengths. From a detailed characterization of the hydrocarbon patterns theinfluence of two different sources could be distinguished. An extrapolationto photochemical age of zero and completion of our data with those from aspeciated VOC inventory yields an estimated [VOC]/NOx sourceratio for Schauinsland of ≈5 [ppbC/ppb]. Comparable[VOC]/NOx ratios are observed in automobile exhaust gasesunder low speed conditions, which points to the important role of trafficunder conditions, when freshly polluted air masses from a near-by city areadvected to the site. From an investigation of the photochemical age of theadvected air masses it becomes clear that there must exist biogenic sourcesof light olefins in the vicinity of the observatory during the vegetationperiod. For propene and the butenes we are able to estimate a lower limit oftheir contributions in terms of reactivity to the total reactivity(∑ [HC](i)⋅ k_OH(i),i=C2-C5) of the measured hydrocarbons. Forlowest pollution levels in summer (acetylene 〈300 ppt, about 40%of the summer values) this source is found to be responsible for15–20% of the total C2–C5reactivity observed at Schauinsland. On the average, this source accountsfor 5–10% of the total C2–C5reactivity.
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  • 9
    ISSN: 1573-0662
    Keywords: Tropospheric ozone ; ozone precursors ; photochemistry ; nitrogen oxides ; rural ozone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The seasonal and diurnal variations of ozone mixing ratios have been observed at Niwot Ridge. Colorado. The ozone mixing ratios have been correlated with the NO x (NO+NO2) mixing ratios measured concurrently at the site. The seasonal and diurnal variations in O3 can be reasonably well understood by considering photochemistry and transport. In the winter there is no apparent systematic diurnal variation in the O3 mixing ratio because there is little diurnal change of transport and a slow photochemistry. In the summer, the O3 levels at the site are suppressed at night due to the presence of a nocturnal inversion layer that isolated ozone near the surface, where it is destroyed. Ozone is observed to increase in the summer during the day. The increases in ozone correlate with increasing NO x levels, as well as with the levels of other compounds of anthropogenic origin. We interpret this correlation as in-situ or in-transit photochemical production of ozone from these precursors that are transported to our site. The levels of ozone recorded approach 100 ppbv at NO x mixing ratios of approximately 3 ppbv. Calculations made using a simple clean tropospheric chemical model are consistent with the NO x -related trend observed for the daytime ozone mixing ratio. However, the chemistry, which does not include nonmethane hydrocarbon photochemistry, underestimates the observed O3 production.
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  • 10
    ISSN: 1573-0662
    Keywords: Matrix isolation/electron spin resonance ; peroxy radicals ; NO3 ; NO2 ; numerical analysis ; atmospheric measurements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Improvements of the matrix isolation/electron spin resonance technique for the measurement of NO2, NO3, and RO2 radicals in the atmosphere are described. The use of D2O instead of H2O as the matrix yields a better spectral resolution and, as a consequence, larger a signal-to-noise ratio as well as better identification of the different species. Reference spectra of the different radicals in H2O and D2O matrices are compared. While a large degree of correlation exists amongst the spectra of the different (unsubstituted and substituted) alkylperoxy radicals, the spectra of HO2, CH3C(O)O2, and NO3 show significant differences that allow their distinction in atmospheric samples. A numerical procedure for the analysis of the composite ESR spectra obtained from atmospheric samples was developed. Subtraction of the dominant NO2 signal is performed by matching a reference NO2 spectrum with respect to amplitude, spectral position, and line width to the sample spectrum. The manipulations are performed with the virtually noise-free reference spectrum and are based on physical information. The residual spectrum is then analyzed for RO2 (and/or NO3) by simultaneously fitting up to six different reference spectra. The method was applied to laboratory samples as well as to atmospheric samples in order to demonstrate the ability of retrieving small amounts of HO2 in the presence of large amounts of NO2 and other peroxy radicals. The new algorithm allowed, for the first time, the identification of the HO2 and CH3C(O)O2 radical in tropospheric air at concentrations ranging up to 40 ppt.
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