Eddy correlation measurements of particulate sulfur fluxes at the 1981 and 1982 Dry DepositionIntercomparison Experiments indicate a strong diurnal variation in deposition velocity (downward flux divided by concentration, at a height near 6 m). Most of the run-to-run variability for data collection periods of 30 min seems to be due to unwanted sensor noise. Systematic changes of fluxes wth height due to possible advection from strong point sources of sulfur can occur but should be quite small. A parameterization for deposition velocity is derived in terms of friction velocity u, and the Obukhov stability length scale L. When the parameterization is applied in conjunction with nearly continuous measurements of mean micrometeorological variables such as wind speed and temperature difference, the resulting long-term mean deposition velocity found is 0.22 + 0.06 cm/s with a variation greater than + 50% from day to day, depending on local atmospheric conditions. Peak deposition velocities greater than 0.5 cm/s occur on windy afternoons. Such values are considerably greater than suggested from wind-tunnel and theoretical investigations, but are similar to past results obtained by use of the same techniques over lush vegetation. Boundary layer convective motions that increase wind gustiness near the surface seem to increase particle deposition velocities considerably. Relatively small deposition velocities are found in neutral and stable atmospheric conditions or over surfaces that lack complex fine structure. INTRODUCTIONSulfur in the lower atmosphere exists in particulate and gaseous forms and is deposited on the surface of the earth by both wet and dry processes [e.g., Garland, 1978]. Since the sulfur component exists in substantial quantities as sulfate aerosol above eastern North America [e.g., Hidy et al., 1978], airborne particulate material could provide a significant portion of the sulfur delivered to sensitive receptors if the deposition velocity, or downward flux divided by concentration at a specified height, were large. The value of the deposition velocity averaged over typical meteorological and surface conditions is a matter of debate [e.g., Sehmel, 1980], especially for particles with diameter 0.05-1.0 um where most of the sulfate associated with long-range transport is found in ambient aerosols. For such particles, the rates of Brownian diffusion very close to surface elements, gravitational settling, and deposition by impaction and interception are thought to be small [e.g., Chamberlain, 1975]; mechanisms that provide a means for deposition velocities to exceed 0.1 cm/s have not been explained and widely accepted. However, as suggested by direct eddy correlation measurements of vertical fluxes at heights of 5-10 m above surface [e.g., Hicks et al., 1982], there is the possibility that deposition velocities for ambient particulate sulfur can be considerably larger than 0.1 cm/s in certain field situations.Argonne National Laboratory (ANL) on sulfate particle fluxes measured by eddy correlation. First, m...

The technique of high energy x-ray diffraction has been used to measure the temperature variation of hydrogen versus deuterium isotopic quantum effects on the structure of water. The magnitude of the effect is found to be inversely proportional to the temperature, varying by a factor of 2.5 over the range 6 to 45 degrees C. In addition, the H216O versus H218O effect has been measured at 26 degrees C and the structural difference shown to be restricted to the nearest neighbor molecular interactions. The results are compared to recent simulations and previously measured isochoric temperature differentials; additionally, implications for H/D substitution experiments are considered.

Molecular dynamics simulations and complementary neutron and x-ray diffraction studies have been carried out within the single phase glass forming range of (Y(2)O(3))(x)(Al(2)O(3))((100-x)), for x = 27 and 30. For x = 27, the experimental Al-O and Y-O coordination numbers are found to be 4.9 ± 0.2 and 6.9 ± 0.4 respectively, compared to 4.4 and 6.8 obtained from the simulation. Similar results were found for x = 30. An R-factor analysis showed that the simulation models agreed to within ∼6% of the diffraction data in both cases. The Al-O polyhedra are dominated by fourfold and fivefold species and the Y-O local coordinations are dominated by sixfold, sevenfold and eightfold polyhedra. Analysis of the oxygen environments reveals a large number of combinations, which explains the high entropy of single phase yttrium aluminate glasses and melts. Of these, the largest variation between x = 27 and 30 is found in the number of aluminum oxygen triclusters (oxygens bonded to three Al) and oxygens surrounded by three Y and a single Al. The most abundant connections are between the AlO(x) and YO(y) polyhedra of which 30% are edge shared. The majority of AlO(x)-AlO(x) connections were found to be corner shared.

The PF(6)(-) salt of a platinum(II) complex changes from yellow to red and becomes intensely luminescent upon exposure to aqueous ClO(4)(-). The response is remarkably selective. Spectroscopic changes are consistent with anion exchange resulting in shortening of the intramolecular PtPt distances between the square planar cations.