Reactions of NO3 Radicals

Nitrate radicals (NO3) are formed by the reaction of O3 and NO2 (Sect. 5.4.2) and play an important role in atmospheric chemistry at nighttime in polluted air. NO3 has an absorption spectrum in the visible region as seen in Sect. (4.2.4) so that daytime concentration is very low since it is easily photodecomposed by sun light. Simultaneously, since the reaction rate constant of NO3 with NO is large, it returns easily to NO2 by NO so that its concentration near NO sources is also very low. NO3 reacts with alkenes and aldehydes to form dinitrates and OH/HO2 radicals at nighttime. Rate constants of fundamental reactions of atmospheric NO3 and related N2O5 are cited in Table 5.6. 

The reaction of NO3 and NO is a simple oxygen atom transfer reaction, 

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Products formed by reaction of NO3 radicals with a-pinene have been identified and include pinane epoxide, 2-hydroxypinane-3-nitrate, and 3-ketopinan-2-nitrate formed by reactions at the double bond, and pinonaldehyde that is produced by ring fission between C-2 and C-3 (Wangberg et al. 1997). These reactions should be viewed in the general context of odd nitrogen to which alkyl nitrates belong (Schneider et al. 1998). 

Wangberg 1,1 Barnes, KH Becker (1997) Product and mechanistic study of the reaction of NO3 radicals with a-pinene. Environ Sci Technol 31 2130-2135. 

Benter, T. and Schindler, R.N. Absolute rate coefficients for the reaction of NO3 radicals with simple dienes, Chem. Phys. Lett., 145 67-70, 1988. 

As discussed in the previous sections reaction of NO3 radicals with organic compounds results in the formation of HNO3 and organic nitrates. In the stratosphere CIO radicals react with N02 to give C10N02 which undergoes hydrolysis. 

Atkinson, R., Aschmann, S.M., Winer, A.M. (1987) Kinetics of the reactions of NO3 radicals with a series of aromatic componnds. Environ. Sci. Technol. 21, 1123-1126. 

Atkinson, R. (1991) Kinetics and mechanisms of the gas-phase reactions of NO3 radical with organic compounds. J. Phys. Chem. Ref. Data 20, 459-507. 

Photolysis direct aqueous photolysis k = 0.011 0.001 min- with u = 60.4 min (Stegeman et al. 1993). Oxidation rate constant k, for gas-phase second order rate constants, kon for reaction with OH radical, k os with NOj radical and ko3 with O3 or as indicated, data at other temperatures see reference l Nos = (7 1) X 10- cm molecule" s" with reference to the reaction of NO3 radical with 2-methyl-2-butene (Japar Niki 1975 Graham Johnston 1978 Carter et al. 1981) koH = 48 X 10" cm molecule" s" with reference to the reaction of OH radical with 2-methyl-2-butene (Atkinson et al. 1979 Carter et al. 1981)... 

Nitrated hydroxyaromatics may enter into the atmosphere from both primary and secondary sources. The formation of nitrophenols and nitrocresols in die combustion processes of motor vehicles has been reported by Tremp et al. (1993). Others primary sources may be combustion of coal, wood, manufacture of phenol-formaldehyde resins, pharmaceuticals disinfectants, dyes and explosives (Harrison et al., 2005). Studies in our and other laboratories have shown that an additional important source of diese compounds in the atmosphere could be the gas-phase OH-radical initiated photooxidation of aromatic hydrocarbons such as benzene, toluene, phenol, cresols and dihydroxybenzenes in the presence of NOx during the daytime as well as the reaction of NO3 radicals widi these aromatics during the night time (Atkinson et al., 1992 Olariu et al., 2002). Once released or... 

Under Romanian-German-Spanish collaboration, experimental investigations of the gas-phase reactions of the NO3 radical with a series of benzenediol compounds were performed. The experiments were carried out in two chamber systems with in situ FT-IR (Fourier Transform -Infrared Spectroscopy) detection of reactants a 1080 1 quartz glass reactor at the Bergische University Wuppertal and in the EUPHORE outdoor smog chamber facility in Valencia/Spain. The kinetics of the reaction of NO3 radicals with three benzenediols using a relative kinetic technique have been investigated. 

Product studies on the reaction of NO3 with isoprene showed that the addition occurs mainly at the 1-position and that 3-methyl-4-nitroxy-2-butenal is the main reaction product (Hjorth). Results from an FTIR spectroscopy study on product formation in the reaction of NO3 radicals with cyclic alkenes provided evidence that dicarbonyls are important products arising from ring opening processes (Ljungstrom). 

Table 4 Rate constants for the reactions of NO3 radicals with inorganic species.

With the exception of phenolic-type compounds the reactions of NO3 radicals with alkylated benzenes will be unimportant under atmospheric conditions. A product study has shown that aromatic aldehydes and aromatic nitrates are the main products of these reactions (Hjorth). 

The fast reaction of NO3 radicals with alkenes was found to give substantial yields of bifunctional carbonyl-nitroxy products and the mechanism of their formation is expected to be relevant also for the conditions of the troposphere. Studies performed by other workers [12] have shown that such organic nitrates may contribute to the atmospheric transport of NOx by acting as reservoirs, releasing NOx by their degradation in the atmosphere, but bifiinctional nitrates may also be subject to fast removal by wet deposition. 

Absolute rate coefficients for the reaction of NO3 radicals with simple dienes,... 

On the identification of oxiranes formed in the reactions of NO3 radicals with alkenes, Ber. Bunsenges. Phys. Chem. 97 (1993) 1447-1453. 

To investigate the kinetics of the gas-phase reactions of NO3 radicals with organic compounds, the method based on thermal decomposition of into NO and... 

Neta P, Huie RE (1986) Rate constants for reactions of NO3 radicals in aqueous solutions. J Phys Chem 90 4644-4648... 

The reaction of NO3 radicals and NO2 in the nighttime polluted atmosphere removes NO3 to form N2O5, which is transformed into nitric acid, HONO2, by reacting with H2O. Therefore, this reaction is important as a process removing NOx from the chain reaction system and forms a HON02reservoir together with the daytime reaction of OH + NO2 + M (Sect. 5.2.4). 

The reaction of NO3 radicals with 3-buten-2-ol has been studied by Hallquist et al. (1996) and Noda et al. (2002). While Hallquist et al. (1996) used both relative and absolute (discharge flow) rate methods, Noda et al. (2002) used a relative rate method. The reaction rate coefficients obtained in these two studies are in very good agreement. An average of the determinations given in table n-D-13 gives A (N03 3-buten-2-ol) = 1.2 X 10 " cm molecule" s with an estimated uncertainty of 30% at 298 K see table ll-D-13. 

Methyl-2-nitrophenol has also been observed as a product of the reaction of NO3 radicals with o-cresol with a yield of 13% which indicates that the channel proceeding by an H-atom abstraction from the —OH group accounts for at least 13% of the reaction (Atkinson et al., 1992b). 

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