Photochemistry nitrate radicals

Extensive research has been conducted into the atmospheric chemistry of organic chemicals because of air quality concerns. Recently, Atkinson and coworkers (1984, 1985, 1987, 1988, 1989, 1990, 1991), Altshuller (1980, 1991) and Sabljic and Glisten (1990) have reviewed the photochemistry of many organic chemicals of environmental interest for their gas phase reactions with hydroxyl radicals (OH), ozone (03) and nitrate radicals (N03) and have provided detailed information on reaction rate constants and experimental conditions, which allowed the estimation of atmospheric lifetimes. Klopffer (1991) has estimated the atmospheric lifetimes for the reaction with OH radicals to range from 1 hour to 130 years, based on these reaction rate constants and an assumed constant concentration of OH... 

The nitrate radical, N03, is an important intermediate in nightime chemistry. Its spectroscopy, photochemistry, and chemistry are reviewed in detail by Wayne et al. (1991) and by Atkinson (1991). 

All these compounds are active participants in environmental photochemistry. Nitrate radicals absorb solar radiation at approximately 600-700 nm and in the excited state dissociate to NOx and oxygen. There are two possible sets of the photodissociation products ... 

Though photochemistry does not take place at night, it is important to note, within the context of tropospheric oxidation chemistry, the potential for oxidation chemistry to continue at night. This chemistry does not lead to the production of ozone, in fact the opposite, but has importance owing to the potential for the production of secondary pollutants. In the troposphere, the main night-time oxidant is thought to be the nitrate radical formed by the relatively slow oxidation of NO2 by O3, viz. 

In addition to the photochemistry of DNA, photoreactions of various cell components, such as membrane proteins, enzymes and other biomolecules may also be relevant to photo-induced cell killing in some cases (Kalisvaart, 2001). In drinking water UV treatment, usually only the photochemical reactions that are induced by direct irradiation are observed. However, if nitrate ion photochemistry (producing OH radicals) is involved, the complex radical chemistry of DNA/RNA and of their fragments may prevail (Pogozelski and Tullius, 1998). 

Graham, R.A., Johnston, H.S. (1978) The photochemistry of the nitrate radical and the kinetics of the nitrogen pentoxide-ozone system. J. Phys. Chem. 82, 254. 

The photochemistry of the nitrate radical, NO3, needs to be incorporated into realistic models of the chemistry of the stratosphere NO3 arises mainly from the reaction of NO2 with O3, and its photolysis products can take part via reactions (37) and (38) in the photochemical cycles upon which the balance of stratospheric... 

Mark G, Schuchmann MN, Schuchmann H-P, von Sonntag C (1990) The photolysis of potassium peroxodisulphate in aqueous solution in the presence of tert-butanol a simple actinometer for 254 nm radiation. J Photochem Photobiol A Chem 55 157-168 Mark G, Korth H-G, Schuchmann H-P, von Sonntag C (1996) The photochemistry of aqueous nitrate revisited. J Photochem Photobiol A Chem 101 89-103 Mark G, Tauber A, Laupert R, Schuchmann H-P, Schulz D, Mues A, von Sonntag C (1998) OH-radical formation by ultrasound in aqueous solution, part II. Terephthalate and Fricke dosimetry and the influence of various conditions on the sonolytic yield. Ultrason Sonochem 5 41-52 MarkG, Schuchmann H-P, von Sonntag C (2000) Formation of peroxynitrite by sonication of aerated water. J Am Chem Soc 122 3781-3782... 

Reduction of metal ions by these radicals then regenerates acetone. In the case of formate ions, the exact photochemical reactions are still relatively unknown—the supposed main products are the HCO radical and 0, deprotonated form of OH (Petersen et al. 2006, Talu and Diyamandoglu 2004). Similarly, even the counter-ions of metal salts can be the source of reactive species (nitrates NO3 produceOH radicals in their complex photochemistry (Mack and Bolton 1999, Marie et al. 1996), whereas halide ions X form X radicals and Ca, (former et al. 1964). 

It is of particular relevance to atmospheric photochemistry that isoprene, a main naturally emitted hydrocarbon, was found to form bifunctional organic nitrates as the predominant products of its reaction with the NO3 radical in air. 

Atmospheric particles very often contain water when they occur as deliquesced aerosol particles, haze, fog, cloud droplets, or even rain droplets (hydrometeors). It has been suggested before that the atmospheric aqueous bulk phase in these systems might also host a lively and important photochemistry which, up to now, has mostly been described insofar as hydroxyl (OH) radicals are generated by the photolysis of nitrate, nitrite, hydrogen peroxide [191-198], and iron-hydroxyl complexes [199]. These processes have been treated in recent overviews such as [200, 201]. 

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