Home Features Environmental exposure to chlorofluoroethanes| NOx and CIOx catalytic| Photodissociation of CF2CI2 and...

Environmental exposure to chlorofluoroethanes| NOx and CIOx catalytic| Photodissociation of CF2CI2 and CFCI3


Environmental exposure to chlorofluoroethanes

The environment’s exposure to chlorofluoroethanes F Sherwood Mario J. Molina, Rowland1975, Reviews of Geophysics 13 (1), 1–35The gases CF2Cl2 and CFCl3 are emitted into the atmosphere after being extensively used in refrigeration and as spray can propellants. These chlorofluoromethanes have extremely long atmospheric residence times due to their chemical inertness and low solubility in water. They can be found in the troposphere in concentrations that roughly correspond to the combined global industrial production to date.

The photolytic decomposition in the stratosphere by ultraviolet light around 2000 appears to be the most significant sink for atmospheric CFCl3 and CF2Cl2. The chlorofluoromethanes undergo photolysis and release chlorine atoms, which starts a lengthy catalytic chain reaction: Cl + O3 ClO + O2.ClO + O Cl + O2, which results in the O3 in the stratosphere is being destroyed overall.

NOx and CIOx catalytic

Via the interaction of the NOx and ClOx catalytic cycles, which occurs when ClO reacts with NO, this chain reaction can be stopped. The Cl-ClO chain is broken when Cl reacts with methane or another hydrogenous substance to produce HCl, and it is then restarted when OH reacts with HCl. According to one-dimensional diffusion calculations, the amount of O3 that is currently depleted as a result of the presence of chlorofluoromethanes is on the order of 1%. If the chlorofluoromethane injection were to continue permanently at the current rates, this depletion would rise to 15% or 20%.

Photodissociation of CF2CI2 and CFCI3

Additionally, the calculations reveal that the photodissociation of CF2Cl2 and CFCl3 does not instantly cause the full stratospheric effect to be felt after their introduction at terrestrial level because of the time interval needed for upward diffusion to reach the 25–30 km level. If the injection of these compounds into the atmosphere were to stop only when there was a discernible loss of stratospheric ozone, the loss would then accelerate and continue to be significant for at least a century.

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