TY  - THES
AB  - Over the last two decades the chemical composition of atmospheric aerosols has changed significantly. Recent field measurements have shown that atmospheric aerosol particles in the upper tropical troposphere contain increasing quantities of organic solutes. At the same time it has been observed that in those aerosols the formation of cirrus clouds is inhibited.
In this work a new process is presented, that might retard or even entirely impede ice nucleation, ice growth as well as the water uptake of atmospheric aerosol particles in the upper troposphere: the formation of glassy aerosol particles.
The glass transition temperatures, Tg, homogeneous ice nucleation temperatures, Thom, and ice melting temperatures, Tm, of various aqueous organic, inorganic and mixed solutions were investigated with a differential scanning calorimeter. The following water-soluble compounds were investigated in binary and ternary aqueous solutions with different mass mixing ratios: glucose, levoglucosan, glutaric acid, 1,4-butanediol, H2SO4, NH4NO3, NH4HSO4, Ca(NO3)2 and NaNO3.
The results of these experiments are presented by means of state diagrams. They reveal that aqueous solutions containing atmospherically relevant inorganic solutes such as NH4NO3 or H2SO4 exhibit only very low Tg-values below 180 K. Therefore, it is expected that atmospheric aerosol particles of such inorganic solutions exist in the liquid or in the crystalline state, but not as glasses. In contrast, aqueous solutions of the investigated organic compounds tend to form glasses at atmospherically relevant temperatures.
In order to apply the laboratory data to the atmospheric situation, the measured phase transition temperatures Tg, Thom and Tm were transformed from the concentration scale to the water activity scale by parameterizing water activities determined experimentally.
The results show that both ice nucleation and ice growth in aqueous organic-enriched aerosol particles can be considerably reduced or even completely inhibited, which can explain the observed inhibition of cirrus cloud formation in the upper tropical troposphere.
DA  - 2008
KW  - Atmosphärisches Aerosol , Troposphäre , Eiswolke , Keimbildung , Glasumwandlung , Wässrige Lösung , Phasendiagramm ,  ,
LA  - ger
PY  - 2008
TI  - Glasbildung in Aerosolpartikeln der oberen Troposphäre
UR  - https://nbn-resolving.org/urn:nbn:de:hbz:361-15866
Y2  - 2024-11-22T05:13:16
ER  -