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- Elgered, Gunnar, 1955, et al.
(författare)
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Geodesy by Radio Interferometry: Water Vapor Radiometry for Estimation of the Wet Delay
- 1991
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 96:B4, s. 6541-6555
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Tidskriftsartikel (refereegranskat)abstract
- An important source of error in very-long-baseline interferometry (VLBI) estimates of baseline length is unmodeled variations of the refractivity of the neutral atmosphere along the propagation path of the radio signals. We present and discuss the method of using data from a water vapor radiometer (WVR) to correct for the propagation delay caused by atmospheric water vapor, the major cause of these variations. Data from different WVRs are compared with estimated propagation delays obtained by Kalman filtering of the VLBI data themselves. The consequences of using either WVR data or Kalman filtering to correct for atmospheric propagation delay at the Onsala VLBI site are investigated by studying the repeatability of estimated baseline lengths from Onsala to several other sites. The lengths of the baselines range from 919 to 7941 km. The repeatability obtained for baseline length estimates shows that the methods of water vapor radiometry and Kalman filtering offer comparable accuracies when applied to VLBI observations obtained in the climate of the Swedish west coast. For the most frequently measured baseline in this study, the use of WVR data yielded a 13% smaller weighted-root-mean-square (WRMS) scatter of the baseline length estimates compared to the use of a Kalman filter. It is also clear that the “best” minimum elevation angle for VLBI observations depends on the accuracy of the determinations of the total propagation delay to be used, since the error in this delay increases with increasing air mass. For use of WVR data along with accurate determinations of total surface pressure, the best minimum is about 20 degrees; for use of a model for the wet delay based on the humidity and temperature at the ground, the best minimum is about 35 degrees.
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- Berglund, Johan, et al.
(författare)
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Kinetics and Mechanism for Manganese-Catalyzed Oxidation of Sulfur(IV) in Aqueous Solution
- 1993
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 1993:32, s. 4527-4538
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics for manganese-catalyzed autoxidation of sulfur(IV) (SO2.nH2O, HSO3-, SO32-) in aqueous solution has been studied spectrophotometrically at 25-degrees-C, 1 < pH < 4, [S(IV)] almost-equal-to 2.3 X 10(-5) M, 1 X 10(-6) M less-than-or-equal-to [Mn(II)] less-than-or-equal-to 1.5 X 10(-3) M, [Mn(III)] less-than-or-equal-to 4 X 10(-8) M, [O2] almost 2.5 X 10(-4) M, and low ionic strength. In the absence of added manganese(III), the kinetic traces display an induction period followed by a reaction first-order in sulfur(IV). Addition of a small amount of manganese(III) increases the rate significantly and suppresses the induction period. At pH 2.4, the first-order rate constant is k(obsd) = k[Mn(II)](1 + B[Mn(III)]0)/(A + [Mn(II)]), where A and B are constants and [Mn(III)]0 is the concentration of initially added manganese(III). The experiments are interpreted in terms of a free-radical chain mechanism. The first step, with rate constant k8 = (1.3 +/- 0.6) X 10(6) m-1 s-1, is a reaction between manganese(III) and a manganese(II) hydrogen sulfite complex with stability constant beta1 = (3 +/- 1) X 10(4) M-1: Mn(III) + MnHSO3+ -->(k8) 2Mn(II) + SO3- + H+. The catalytic activity of Mn(III/II) may be explained by formation of an oxo- (or hydroxo-) bridged mixed-valence precursor complex Mn(III)-O-Mn(II)-HSO3, in which bridged electron transfer produces the SO3 radical. When [Fe(III)] < 10(-6) M is added to the reacting system, the oxidation rate becomes much faster than the sum of the individual contributions from the manganese and iron catalyses; i.e., a synergistic effect is displayed. Initiation of the manganese-catalyzed oxidation in the absence of initially added manganese(III) is shown to be due to a trace impurity of ca. (1-2) x 10(-8) M iron(III). The SO3- radical is generated by the oxidation of sulfur(IV) by iron(III). In subsequent steps, manganese(II) is oxidized to manganese(III) by SO5- formed by oxidation of SO3 with dissolved oxygen. Computer simulation of the overall kinetics shows that an iron(III) concentration of 2 x 10(-8) M is indeed sufficient to initiate the manganese-catalyzed oxidation and explains the autocatalysis. At pH 4.0, the first-order rate constant is k(obsd) = (k[Mn(II)] + k[Mn(II)]2)/(A + [Mn(II)]). The quadratic manganese(II) term indicates formation of a sulfito-bridged manganese(II) complex, MnSO3Mn2+, which can also be attacked by manganese(III), forming SO3- radicals. Several discrepancies in previous literature may be explained by the reaction mechanism derived.
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- Berglund, Johan, et al.
(författare)
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Manganese(II)- and Nickel(II)-Catalyzed Oxidation of S(IV) by Oxygen in Aqueous Solution : A contribution to subproject HALIPP
- 1991
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Ingår i: Transport and Transformation of Pollutants in the Troposphere : Proc. EUROTRAC Symposium '90, Garmisch-Partenkirchen, Germany, April 2-5, 1990 - Proc. EUROTRAC Symposium '90, Garmisch-Partenkirchen, Germany, April 2-5, 1990. - 9051030584 ; , s. 295-298
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Konferensbidrag (refereegranskat)abstract
- Manganese(II)- and nickel(II)-catalyzed oxidation of sulfur(IV) by oxygen in aqueous solution at pH 4.5 has been studied, as a model for oxidation of sulfur(IV) to sulfuric acid at the natural pH of the droplets in most atmospheric aqueous systems.
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| 10. |
- Berndtsson, Ronny
(författare)
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Small-scale spatial patterns of bulk atmospheric deposition
- 1993
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Ingår i: Journal of Environmental Quality. - : Wiley. - 0047-2425. ; 22:2, s. 349-360
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Tidskriftsartikel (refereegranskat)abstract
- In total 14 bulk atmospheric deposition collectors were distributed over the city of Lund (about 20 km~) in the south of Sweden during September 1980 to June 1981. The observations were made to investigate small-scale spatial variability of atmospheric deposition. Monthly bulk deposition samples were analyzed for CI, Ptot, Zn, Cu, and Pb.Correlation analysis shows that the spatial scale for the variation pat-tern is of the order > 10 km for precipitation and CI, and about 2 kmfor Ptot and metals. This indicates that remote sources with a general large-scale deposition pattern are dominating for CI deposition and that local sources dominate for P,o,, Zn, Cu, and Pb. The total atmospheric deposition in the investigated urban area is assumed to be superposed by three components: (i) regional background, (li) urban background, and (iii) urban point deposition. The urban background deposition may be considerable in relation to regional background deposition. The urban point sources may represent deposition rates of twice or more of the total deposition.
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