Heterogeneous Chemistry in the Atmosphere
Chemical kineticists have long been involved in the study of the chemistry of the atmosphere. This involvement is both natural and important and has led to quantitative mechanistic understanding of many atmospheric phenomena. Historically the atmosphere had been regarded as essentially a gas phase reactor, with surface phenomena a laboratory hindrance to obtaining measurements that were applicable to the real situation. Relatively recent understanding has changed this view. In this paper, emphasis will be given to results from our laboratory using Knudsen cell techniques to study interactions of gaseous species with atmospherically relevant liquid sulfuric acid-water solutions and soot particles representative of those found (or postulated) in some specific atmospheric venues.
We have studied the interactions of HNO3, HCl and HBr with liquid sulfuric acid surfaces using both time dependent uptake and equilibrium vapor pressure methods in a Knudsen cell reactor equipped with mass spectrometric detection. Measured solubilities will be presented as Henry’s law coefficients along with thermochemical parameters.
Soot particles emitted by the current and projected fleet of subsonic aircraft may impact both the chemistry and radiative properties of the upper troposphere and lower stratosphere by providing nucleation centers for water-based aerosols. We have studied the uptake of water on soot samples before and after exposure to exhaust gas species such as sulfur dioxide and nitrogen dioxide as well as to ozone. In experiments performed to date, we see no change in the interaction of soot with water after such exposure. However, when the soot is exposed to HNO3 or H2SO4, water uptake is greatly enhanced. Additionally, we find some interesting chemical transformations when HNO3 interacts with soot.
KeywordsSoot Particle Sulfate Aerosol Knudsen Cell Uptake Coefficient Ozone Destruction
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