Hydroxyl radical number density

Sonoelectrochemistry has been employed in a number of fields such as in electroplating for the achievement of deposits and films of higher density and superior quality, in the deposition of conducting polymers, in the generation of highly active metal particles and in electroanalysis. Furtlienuore, the sonolysis of water to produce hydroxyl radicals can be exploited to initiate radical reactions in aqueous solutions coupled to electrode reactions. 

The temperature profile strongly influences those reactions whose rate coefficients have large activation energies. As will be shown in Sections IV, V, and VI, a number of reaction paths, while dominant in the lower troposphere, lose their importance with increasing altitude as the temperature drops sharply. Particularly affected are the altitude profiles of the hydroxyl radical, formaldehyde, and nitric oxide number densities. 

Molecular hydrogen is assumed to be well mixed in the troposphere, with a mixing ratio of 0.4 to 0.6 ppm [Junge (128) and Scholz, Ehhalt, Heidt, and Martell (219)]. Koyama (142) found that swamps and paddies are very small natural sources. Levy (153) proposed both an atmospheric source (photodissociation of formaldehyde) and an atmospheric sink (oxidation by hydroxyl radical). From daily average number densities for the hydroxyl radical and a daily average hydrogen production rate,... 

Using daily average number densities of the hydroxyl radical, n(OH) = 3.7 x 106, for the lower troposphere (Levy (153)], we find that the residence time for H2S due to R12 ranges from 7 to 15 hr and is in harmony with previous estimates. 

Table 5-2 compares rate coefficients for reactions of oxygen atoms, ozone, and hydroxyl radicals with selected hydrocarbons, and the corresponding rates for the loss of the same hydrocarbons calculated with appropriate steady-state values for the number densities of O, 03, and OH. The rates of OH radicals exceed those of the other reactants for almost every hydrocarbon listed. The OH number density adopted, 2 x 106 molecules/cm3, corresponds to that expected at noon on a clear summer day in the natural atmosphere at 30° northern latitude. 

The application of the quasi-cw, ultraviolet laser source to kinetic studies was demonstrated in the laser photolysis/laser-induced fluorescence experiments shown schematically in Figure 2. Chemical reactions were initiated by 193-nm photolysis of N2O in N20/H20/hydrocarbon/helium gas mixtures. The 0( D) atoms formed by photodissociation rapidly converted to OH through reaction with H2O, and time-resolved OH concentrations were measured as functions of hydrocarbon number density by laser-induced fluorescence. Hydroxyl radical fluorescence was excited by pumping the nearly coincident Pjl, Qi3, and Qi3 (0,0) band transitions at 308.16 nm, (15) and radiation emanating from the reaction volume in a downward direction was skimmed by black-anodized collimators, focused by quartz lenses, selected by a bandpass filter (308.3 nm peak, 8 nm FWHM), and detected by an RCA 8850 photomultiplier operating in the photon-counting mode. 

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