Nitrate radical measurement

The input of formaldehyde into the environment is counterbalanced by its removal by several pathways. Formaldehyde is removed from the air by direct photolysis and oxidation by photochemically produced hydroxyl and nitrate radicals. Measured or estimated half-lives for formaldehyde in the atmosphere range from 1.6 to 19 hours, depending upon estimates of radiant energy, the presence and concentrations of other pollutants, and other factors (Atkinson and Pitts 1978 DOT 1980 EPA 1982 Lowe et al. 1980 Su et al. 1979). When released to water, formaldehyde will biodegrade to low levels in a few days (Kamata 1966). In water, formaldehyde is hydrated it does not have a chromophore that is capable of absorbing sunlight and photochemically decomposing (Chameides and Davis 1983). 

The kinetics of the various reactions have been explored in detail using large-volume chambers that can be used to simulate reactions in the troposphere. They have frequently used hydroxyl radicals formed by photolysis of methyl (or ethyl) nitrite, with the addition of NO to inhibit photolysis of NO2. This would result in the formation of 0( P) atoms, and subsequent reaction with Oj would produce ozone, and hence NO3 radicals from NOj. Nitrate radicals are produced by the thermal decomposition of NjOj, and in experiments with O3, a scavenger for hydroxyl radicals is added. Details of the different experimental procedures for the measurement of absolute and relative rates have been summarized, and attention drawn to the often considerable spread of values for experiments carried out at room temperature (-298 K) (Atkinson 1986). It should be emphasized that in the real troposphere, both the rates—and possibly the products—of transformation will be determined by seasonal differences both in temperature and the intensity of solar radiation. These are determined both by latitude and altitude. 

Platt UF, AM Winer, HW Biermann, R Atkinson, JN Pitts, Jr (1984) Measurement of nitrate radical concentrations in continental air. Environ Sci Technol 18 365-369. 

The detailed model was constructed as described by Carslaw et al. (1999, 2002). Briefly, measurements of NMHCs, CO and CH4 were used to define a reactivity index with OH, in order to determine which NMHCs, along with CO and CH4, to include in the overall mechanism. The product of the concentration of each hydrocarbon (and CO) measured on each day during the campaign and its rate coefficient for the reaction with OH was calculated. All NMHCs that are responsible for at least 0.1% of the OH loss due to total hydrocarbons and CO on any day during the campaign are included in the mechanism (Table 2). Reactions of OH with the secondary species formed in the hydrocarbon oxidation processes, as well as oxidation by the nitrate radical (NO3) and ozone are also included in the... 

FIGURE 7.12 Comparison of measured (Platt et al., 1984) and predicted nitrate radical concentrations at Edwards Air Force Base, California, May 23-24, 1982. The dashed line is the model prediction without the unimolecular decomposition of NO, and the solid line is that with the decomposition (adapted from Russell et at., 1986). 

Mihelcic, D., D. Klemp, P. Musgen, H. W. Patz, and A. Volz-Thomas, Simultaneous Measurements of Peroxy and Nitrate Radicals at Schauinsland, J. Atmos. Chem., 16, 313-335 (1993). 

The use of the sun or moon as the light source allows one to measure the total column abundance, i.e., the concentration integrated through a column in the atmosphere. This approach has been used for a number of years (e.g., see Noxon (1975) for NOz measurements) and provided the first measurements of the nitrate radical in the atmosphere (Noxon et al., 1978). As discussed later in this chapter, such measurements made as a function of solar zenith angle also provide information on the vertical distributions of absorbing species. Cloud-free conditions are usually used for such measurements as discussed by Erie et al. (1995), the presence of tropospheric clouds can dramatically increase the effective path length (by an order of... 

N03 As discussed earlier, the nitrate radical can be measured using visible spectroscopy and its absorption bands, particularly the one at 662 nm. As a result, visible absorption spectroscopy has been the method of measurement used most extensively for NOv As discussed shortly, a matrix isolation technique has also been applied with success in some studies. 

The syntheses of iron isonitrile complexes and the reactions of these complexes are reviewed. Nucleophilic reagents polymerize iron isonitrile complexes, displace the isonitrile ligand from the complex, or are alkylated by the complexes. Nitration, sulfonation, alkylation, and bromina-tion of the aromatic rings in a benzyl isonitrile complex are very rapid and the substituent is introduced mainly in the para position. The cyano group in cyanopentakis(benzyl isonitrile)-iron(ll) bromide exhibits a weak "trans" effect-With formaldehyde in sulfuric acid, benzyl isonitrile complexes yield polymeric compositions. One such composition contains an ethane linkage, suggesting dimerization of the transitory benzyl radicals. Measurements of the conductivities of benzyl isonitrile iron complexes indicate a wide range of A f (1.26 e.v.) and o-o (1023 ohm-1 cm.—1) but no definite relationship between the reactivities of these complexes and their conductivities. 

The very low value of Ashmore and Burnett is difficult to explain. It is easy to demonstrate that the discrepancy is not resolved by assuming the N03 intermediate in nitrogen dioxide decomposition is the pernitrite radical, in contradistinction to the symmetric nitrate radical. Their calculation of k5 depended on an experimentally obtained value for k 5 and an equilibrium constant K5- 5 calculated from thermodynamic properties for N03 measured by Schott and Davidson and Ray and Ogg. These results, obtained in a nitrogen pentoxide system, pertain to the nitrate radical, not the pernitrite radical. Guillory and Johnston176 reported an equilibrium constant based on estimated... 

Kleno, J. and Wolkoff, P. (2004) Changes in eye blink frequency as a measure of trigeminal stimulation by exposure to limonene oxidation products, isoprene oxidation products and nitrate radicals. International Archives of Occupational and Environmental Health, 77 (4), 235-43. 

The PANs are known to be quite sensitive to walls in laboratory studies, and therefore are likely to react on aerosol surfaces. The PANs are very soluble in nonpolar organics. PANs can undergo important oxidation reactions on soot surfaces, leading to the formation of oxidized and nitrated polynuclear aromatic hydrocarbons which can be highly mutagenic. " The measurement of the PANs, as well as more usual oxidants such as O3, nitrate radical, and hydroxyl radical, is an important part of the characterization of potentially hazardous air pollutants. 

Use of a stopped-flow technique to measure the rate constants at room temperature for reactions between the nitrate radical and various organic species,... 

Along these lines, We have explored the possibility that red wine and red wine phenolics (e.g., anthocyanin fraction) promoted the formation of NO from nitrite in a pH-dependent and concentration-dependent way. This has been substantiated in vivo in healthy volunteers by measuring NO in the air expelled from the stomach, following consumption of wine and nitrate, as measured by chemiluminescence (Gago et al, 2007). Structure-activity studies revealed that the formation of NO from nitrite directly correlates with the reduction potential of the several phenols tested, including dimers B2, B5, B8, catechin, epicatechin, and quercetin, among others (results not published). EPR studies showed that, mechanistically, the reaction involves the one-electron reduction of nitrite to NO by the polyphenols and the concomitant formation of phenol-derived phenoxyl radicals (Gago et al, 2007) (Fig. 11.1). 

Boyd, A.A., C.E. Canosa-Mas, D. King, R.P. Wayne, and M.R. Wilson (1991), Use of a stopped-flow technique to measure the rate constants at room temperature for reactions between the nitrate radical and various organic species, J. Chem. Soc., Faraday Trans. 87,... 

Protein tyrosine residues constitute key targets for peroxynitrite-mediated nitrations. Attack of various free radicals (ONOO-, N02 ) upon tyrosine generates 3-nitrotyrosine, which can be measured immunologically or by GC/MS or HPLC techniques. The detection of 3-nitrotyrosine was considered a biomarker of peroxynitrite action in vivo. Similarly, attack of HOC1 and HOBr on tyrosine generates chlorotyro-sine and bromotyrosine, respectively, both of which are measured most accurately by GC-MS. 

The ability of MPO to catalyze the nitration of tyrosine and tyrosyl residues in proteins has been shown in several studies [241-243]. However, nitrite is a relatively poor nitrating agent, as evident from kinetic studies. Burner et al. [244] measured the rate constants for Reactions (24) and (25) (Table 22.2) and found out that although the oxidation of nitrite by Compound I (Reaction (24)) is a relatively rapid process at physiological pH, the oxidation by Compound II is too slow. Nitrite is a poor substrate for MPO, at the same time, is an efficient inhibitor of its chlorination activity by reducing MPO to inactive Complex II [245]. However, the efficiency of MPO-catalyzing nitration sharply increases in the presence of free tyrosine. It has been suggested [245] that in this case the relatively slow Reaction (26) (k26 = 3.2 x 105 1 mol-1 s 1 [246]) is replaced by rapid reactions of Compounds I and II with tyrosine, which accompanied by the rapid recombination of tyrosyl and N02 radicals with a k2i equal to 3 x 1091 mol-1 s-1 [246]. 

During SOAPEX-2, measurements of the free-radicals OH, HO2, HO2+XRO2, NO3, IO and OIO were supported by measurements of temperature, wind speed and direction, photolysis rates (j D) and j(N02)), water vapor, O3, HCHO, CO, CH4, NO, NO2, peroxyacetyl nitrate (PAN), a wide range of NMHCs, organic halogens, H2O2, CH3OOH and condensation nuclei (CN). 

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