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  • 1
    Electronic Resource
    Electronic Resource
    Interhemispheric asymmetry in OH abundance inferred from measurements of atmospheric 14 CO (1992)
    [s.l.] : Nature Publishing Group
    Nature 356 (1992), S. 50-52 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] We extracted CO in situ from 1.5-m3 air samples following the method of Stevens and Krout9. In essence, after removal of at least 99.9999% of atmospheric CO2, the CO content is oxidized over I2O5 to CO2, which is subsequently trapped cryogeni-cally. This quantitative extraction procedure provided ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/356050a0
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  • 2
    Electronic Resource
    Electronic Resource
    On the Exchange of NO3 Radicals with Aqueous Solutions: Solubility and Sticking Coefficient (1998)
    Springer
    Journal of atmospheric chemistry 29 (1998), S. 17-43 
    Details
    ISSN: 1573-0662
    Keywords: nitrate radical ; solubility ; sticking coefficient ; redox potential ; heterogeneous removal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The exchange of NO3 radicals with the aqueous-phase was investigated at room temperature (293 K) in a series of wetted denuders. From these experiments, the uptake coefficient of NO3 was determined on 0.1 M NaCl solutions and was found to be γ(NO3) ≥ 2 × 10-3 in good agreement with recent studies. The Henry coefficient of NO3 was estimated to be KH(NO3) = 1.8 M · atm-1, with a (2σ) uncertainty of ±3 M · atm-1. From the upper limit for the Henry coefficient (KH = 5 M · atm-1) and available thermodynamic data, the redox potential of dissolved NO3/NO 3 − is estimated to be in the range of 2.3 to 2.5 V. This range is at the lower boundary of earlier estimates. The results are discussed in the light of a recent publication. Based on our data and a model of the transport and chemistry in the liquid film, an upper limit is derived for the product of the Henry coefficient KH and the rate coefficient k 10 of the potential reaction NO3 + H2O → HNO3 + OH. For KH = 0.6 M · atm-1, we find k 10 〈 0.05 s-1 · atm-1, i.e., about 100 times smaller than what was suggested by Rudich and co-workers. Because of its small solubility, heterogeneous removal of NO3 is only important under conditions where the dissolved NO3 is removed quickly from equilibrium, for example by reactions with Cl− or HSO 3 − ions in the liquid-phase. Otherwise, heterogenous removal should mainly proceed via N2O5.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005860312363
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  • 3
    Electronic Resource
    Electronic Resource
    A photoelectric detector for the measurement of photolysis frequencies of ozone and other atmospheric molecules (1989)
    Springer
    Journal of atmospheric chemistry 8 (1989), S. 203-227 
    Details
    ISSN: 1573-0662
    Keywords: Atmosphere ; photolysis ; ozone ; nitrogen dioxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Photoelectric detectors for the measurement of photolysis frequencies of different trace gases in the atmosphere are described. They exhibit uniform response characteristics over one hemisphere (2π sr) and wavelength characteristics closely matched to those of the photolysis frequencies J O1D, J NO2, and J NO3, respectively. Absolute calibration of the J O1D detector was performed by chemical actinometry with an accuracy of ±16 percent. Simultaneous measurements of J NO2 and J O1D are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00051494
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  • 4
    Electronic Resource
    Electronic Resource
    On the Budget of OH Radicals and Ozone in an Urban Plume from the Decay of C5–C8 Hydrocarbons and NOx (1997)
    Springer
    Journal of atmospheric chemistry 28 (1997), S. 263-282 
    Details
    ISSN: 1573-0662
    Keywords: ozone ; hydrocarbons ; NOx ; photochemistry ; OH-radicals ; budget
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Simultaneous measurements of ozone and ozoneprecursors were made during a field campaign atSchauinsland in the Black Forest and in the valleynorth of Schauinsland that channels the flow ofpolluted air from the city of Freiburg to the site.From the decay of hydrocarbons and NOx between the twomeasuring sites and the known rate coefficients, theconcentration of OH radicals was calculated. From abudget analysis of OH and HOx it is concluded that therelatively high OH concentrations (5–8 ×106cm-3) in the presence of high NO2concentrations cannot be explained by the knownprimary sources. The budget can be closed if efficientrecycling of OH via HO2 is assumed to occur andthat, based on the measured hydrocarbons, 2 HO2molecules are formed for each OH radical that reactswith a hydrocarbon molecule. This assumption is inaccordance with the budget of Ox obtained from ourmeasurements and with results from earliermeasurements of alkylnitrates and peroxy radicals atSchauinsland. A possible conclusion is that the decayof precursors and production of photooxidants in urbanplumes proceeds at a faster rate than is currentlyassumed. The potential role of biogenichydrocarbons for the radical budget is alsodiscussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005821522256
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  • 5
    Electronic Resource
    Electronic Resource
    Simultaneous measurements of peroxy and nitrate radicals at Schauinsland (1993)
    Springer
    Journal of atmospheric chemistry 16 (1993), S. 313-335 
    Details
    ISSN: 1573-0662
    Keywords: HO2-, RO2-, and NO3-radicals ; tropospheric measurements ; matrix isolation/electron spin resonance ; nighttime chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We present simultaneous field measurements of NO3 and peroxy radicals made at night in a forested area (Schauinsland, Black Forest, 48° N, 8° N, 1150 ASL), together with measurements of CO, O3, NO x , NO y , and hydrocarbons, as well as meteorological parameters. NO2, NO3, HO2, and ∑(RO2) radicals are detected with matrix isolation/electron spin resonance (MIESR). NO3 and HO2 were found to be present in the range of 0–10 ppt, whilst organic peroxy radicals reached concentrations of 40 ppt. NO3, RO2, and HO2 exhibited strong variations, in contrast to the almost constant values of the longer lived trace gases. The data suggest anticorrelation between NO3 and RO2 radical concentrations at night. The measured trace gas set allows the calculation of NO3 and peroxy radical concentrations, using a chemical box model. From these simulations, it is concluded that the observed anthropogenic hydrocarbons are not sufficient to explain the observed RO2 concentrations. The chemical budget of both NO3 and RO2 radicals can be understood if emissions of monoterpenes are included. The measured HO2 can only be explained by the model, when NO concentrations at night of around 5 ppt are assumed to be present. The presence of HO2 radicals implies the presence of hydroxyl radicals at night in concentrations of up to 105 cm−3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01032628
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  • 6
    Electronic Resource
    Electronic Resource
    Climatology of Ozone, PAN, CO, and NMHC in the Free Troposphere Over the Southern North Atlantic (1997)
    Springer
    Journal of atmospheric chemistry 28 (1997), S. 245-262 
    Details
    ISSN: 1573-0662
    Keywords: free troposphere ; ozone ; non methane hydrocarbons ; peroxyacetylnitrate ; carbon monoxide ; photo chemistry ; North Atlantic ; seasonal cycle ; long range transport ; back-trajectories ; photochemical age
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Free tropospheric measurements of ozone, peroxyacetylnitrate andprecursors (CO, NMHC) that were made within the framework of the EUROTRACsub-project TOR (Tropospheric Ozone Research) between 1990 and 1995 at theGAW station Izana, Tenerife (28°18′N, 16°30′W) arediscussed. The average annual cycles reveal the importance of transport fromnorthern mid-latitudes and the role of photo-chemistry. According toair-mass trajectories, which were supplied to us from AEROCE(Atmosphere/Ocean Chemistry Experiment), transport from northernmid-latitudes is associated with high precursor concentrations in winter,whereas ozone concentrations in winter are not much influenced by transportpatterns, suggesting a rather uniform distribution over the northern part ofthe Northern Hemisphere around mean value of 43 ± 5 ppb. In summer,high ozone concentrations of up to 90 ppb are often encountered duringtransport from north, while the levels of precursors are much lower than inwinter, because of photochemical destruction. Trajectories from southerlylatitudes and the Sahara usually have the lowest ozone concentrationsassociated with them.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005801515531
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  • 7
    Electronic Resource
    Electronic Resource
    Numerical analysis of ESR spectra from atmospheric samples (1990)
    Springer
    Journal of atmospheric chemistry 11 (1990), S. 271-297 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00118353
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  • 8
    Electronic Resource
    Electronic Resource
    Long-Term Measurements of Light Hydrocarbons (C2–C5) at Schauinsland (Black Forest) (1997)
    Springer
    Journal of atmospheric chemistry 28 (1997), S. 135-171 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005878018619
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  • 9
    Electronic Resource
    Electronic Resource
    Preparation of organic nitrates from alcohols and N2O5 for species identification in atmospheric samples (1993)
    Springer
    Journal of atmospheric chemistry 16 (1993), S. 349-359 
    Details
    ISSN: 1573-0662
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Several mono- and bifunctional organic nitrates of atmospheric interest were prepared in a one-step synthesis, based on the reaction of alcohols with N2O5 (dinitrogen pentoxide) at low temperatures. The method is well suitable for micro-scale preparations. The compounds were characterized by GC/ECD, GC/NO y -specific detection, and GC/CI (chemical ionization) mass spectrometry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01032630
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  • 10
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    IL-4 abrogates TH17 cell-mediated inflammation by selective silencing of IL-23 in antigen-presenting cells (2015)
    National Academy of Sciences
    Details
    Publication Date: 2015-02-02
    Description: Interleukin 4 (IL-4) can suppress delayed-type hypersensitivity reactions (DTHRs), including organ-specific autoimmune diseases in mice and humans. Despite the broadly documented antiinflammatory effect of IL-4, the underlying mode of action remains incompletely understood, as IL-4 also promotes IL-12 production by dendritic cells (DCs) and IFN-γ–producing TH1 cells in vivo. Studying the impact of IL-4 on the polarization of human and mouse DCs, we found that IL-4 exerts opposing effects on the production of either IL-12 or IL-23. While promoting IL-12–producing capacity of DCs, IL-4 completely abrogates IL-23. Bone marrow chimeras proved that IL-4–mediated suppression of DTHRs relies on the signal transducer and activator of transcription 6 (STAT6)-dependent abrogation of IL-23 in antigen-presenting cells. Moreover, IL-4 therapy attenuated DTHRs by STAT6- and activating transcription factor 3 (ATF3)-dependent suppression of the IL-23/TH17 responses despite simultaneous enhancement of IL-12/TH1 responses. As IL-4 therapy also improves psoriasis in humans and suppresses IL-23/TH17 responses without blocking IL-12/TH1, selective IL-4–mediated IL-23/TH17 silencing is promising as treatment against harmful inflammation, while sparing the IL-12–dependent TH1 responses.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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