Atmospheric Chemistry

Rate constants for bimolecular reactive and energy transfer collisions are required for models of the atmosphere and to interpret measurements of the atmospheric composition.

Reactive Collisions (an example)
Models of the mesosphere and upper stratosphere predict concentrations of OH, O3, and HO2 that do not agree with recently available concentrations extracted from satellite observations. These chemical species have such short chemical lifetimes that their concentration is controlled by chemistry as opposed to transport. Sensitivity analysis shows the reactions O+HO2 and OH+HO2 are the key players in the chemistry of the HOx cycle, which controls the composition of the mesosphere and the upper stratosphere. Laboratory experiments to measure the rate constants of these reactions as a function of temperature are currently under way with support with NASA.

Energy Transfer Collisions
The absorption of sunlight, photodissociation of the excited molecules, and the chemical reaction of the dissociation products drive the reactivity of the earth's atmosphere. Electronically and vibrationally excited atoms and molecules are produced in the earth's atmosphere by solar radiation and chemical reaction; some of these excited species radiate light. The spectral distribution of this light and the reactivity of the atmosphere are both controlled by energy transfer collisions. Energy transfer collisions are also important to quantitatively understand optical measurements of trace species in the atmosphere. Laboratory measurements to understand key energy transfer pathways and validate atmospheric sensor strategies are sponsored by NASA. Strategies for detecting OH and NO_x in the troposphere have been developed for field measurements.
 

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Technical Contact:
Gregory P. Smith
(650) 859-3496
gregory.smith@sri.com