Abstract
Atmospheric chemistry deals with chemical compounds, especially trace gases, in the atmosphere and their origin, chemical reactions, accumulation and distribution.
The photochemistry and kinetics of free radical r eactions among trace substances are important for understanding chemical transformation of trace substances into other compounds, and finally, the ir removal from the atmospheric domain.
In this paper, rate constants a nd mechanisms for reactions of free radicals with other gases related to atmospheric chemistry will be reported. Studies are carried out using a photoionization mass spectrometer coupled with a discharge-flow or pulsed laser photolysis system. The photoionization mass spectrometer can be a very selective and sensitive detector of many free radicals in the gas phase. Vacuum ultraviolet light from rare gas resonance lines is used to ionize the radicals, rather than an electron beam, in order to avoid the interference from fragments heavier stable molecules. Rate constants for reactions o f alkyl, hydroxyalkyl, substituted methyl, formyl, and acetyl radicals with atomic and molecular oxygen have been measured and the reactivity of those reactions will be discussed by the correlation with ionization potential and electronegativities of radicals. In addition, rate constants for reactions of peroxy radicals such as HO2 and CH3O2 with NO have been determined. Contribution of each reaction to atmospheric chemistry will be discussed.
Finally, an experime ntal study of ozone depletion by CFCl3 using a 6m-3 photochemical chamber is reported in order to show the decay of ozone by a catalytic cycle involving Cl and ClO radicals.
