Atmospheric Chemistry Group
Scientific Equipment
Refractive indices of H2SO4/HNO3/H2O solutions to stratospheric temperatures

by Ulrich K. Krieger, Juliane C. Mössinger, Beiping Luo, Uwe Weers, and Thomas Peter, 2000


Java programming by Dora Farkas 		This page offers a model which uses the Lorentz-Lorenz relation to estimate the refractive index of aqueous H2SO4 and HNO3 solutions (5-70 wt%) for wavelengths from the near ultraviolet to the near-infrared (250-2000 nm) and for the temperatures from 370 K to stratospheric temperatures (185 K). The molecular refractivities of the involved species are based on data of the binary solutions at room temperature. For extrapolation to low temperatures a careful estimate of the density of the ternary solutions has been performed. The accuracy of the model is predicted to be better than 0.15 % (see abstract)

To run this model you have to have a Web Browser which supports Java 1.1.2. If you only see a grey square next to this text then you better select the-not-so-flashy-JavaScript version that runs with older browsers like Netscape Navigator 3.0. The Java source code can be found here.

Trapping of Individual Aerosol Particles (ALCATRAS)


A schematic of the experimental system is shown in the figure on the left (click for a larger image). A charged aerosol (radius approx. 3 microns) is levitated in a double-ring electrodynamic balance. Three collinear laser beams illuminate the particle from below (HeNe @ 633 nm, Ar+ @ 488 nm, and a Tunable-Diode-Laser @ 763-787 nm). The balance is placed in a three wall glass chamber, with a cooling liquid flowing through the inner walls and an isolation vacuum between the outer walls. A constant flow of an appropriate gas mixture is pumped continuously through the chamber, the total pressure can be varied between 50 and 1000 hPa.
Four methods are used to characterize the aerosol: the DC voltage applied to compensate the gravitational force is proportional to the mass of the particle, Mie phase functions are used to deduce the radius of the aerosol and to detect phase changes, Raman spectroscopy is employed to measure its composition. Additionally the radius and refractive index of a spherical particle can be measured with high precision using the tunable diode laser (TDL) and analyzing the Mie resonance spectra [Krieger et al., 1995]. An example of the combined measurements is shown in the figure on the left (click for a larger image): here the uptake of water of a H2SO4/H2O aerosol at 2 hPa and its cooling along the ice-liquid coexistence line to 158 K was studied.
contact: Christina Colberg, Ulrich Krieger See the ALCATRAS page for more details of the expriment.

Raman microscopy on large particle ensembles

A regular droplet array is produced by so-called micro contact printing (see schematic drawing on the left):
  1. a stamp is filled with a thiole with hydrophilic endgroup (i.e. 11-Hydroxy-undecane thiole)
  2. then pressed on a gold coated silicon wafer
  3. removed after a short while
  4. the wafer is then treated with another thiole solution, this time with hydrophobic endgroup (i.e. undecane-thiole)
Now only that parts of the surface are wettable by polar fluids (water, or H2SO4), that were coated with the hydrophilic endgroup thioles. The resulting droplets can be seen on the micrograph on the right.
contact: Christian Braun, Thomas Koop, Daniel Knopf

Photoacoustic spectroscopy
Fluorescence spectroscopy
Rutherford Backscattering Spectrometry (RBS)

Trace gas uptake on ice surfaces studied by RBS
Collaboration: W. A. Lanford, SUNY at Albany, Albany, N.Y., U.S.A.
Two fields will be pursued: (a) Measurements of solubility and diffusion constants of different trace gases (HCl, SO2, ...) in ice and in acid hydrates under atmospheric conditions, (b) Investigations for the existence and characterization of the quasi-liquid layer (QLL) on ice surfaces. The samples (polycrystalline ice samples, ice single crystals and hydrates of sulfuric acid and nitric acid will be examined in the helium or proton beam of a linear accelerator by Rutherford backscattering (RBS). This technique permits the non-destructive measurement of absolute concentration profiles with a depth resolution of 30Å over a total depth of about 10.000Å. From such concentration profiles the diffusion constant (D) and the solubility (Henry’ s law constant, H) can be determined independently, if the gas phase is known or measured (mass spectroscopy). These are quantities needed as a function of temperature, trace gas concentration and morphology of the ice for modeling atmospheric chemistry e.g. in polar regions or cirrus clouds. Apart from the measurement of the quantities D and H the quasi liquid layer on ice will be examined. Concentration profiles of a trace gas in the solid phase will be measured in the proximity of the coexistence line between ice and the appropriate aqueous solution of the trace gas. By the differences in the diffusion constants these concentration profiles should differ depending on how the surface of the ice is represented: by an expanded, relatively homogeneous liquid film with sharp transitions both to the solid and the gaseous phase, or by a gradual reduction of the crystal order to the gaseous phase.

learn something about RBS:
contact: Thomas Huthwelker, Ulrich Krieger

last updated 29-JAN-2001
Christian Braun