Nitrogen dioxide aqueous phase reactions

Nitrogen Oxide Reactions. Examination of possible aqueous-phase reactions of nitrogen dioxide and peroxyacetyl nitrate has revealed no reactions of importance to cloud chemistry (21,22). This situation is a consequence of the low solubilities and/or low reactivities of these gases with substances expected to be present in cloudwater, although studies with actual precipitation samples would be valuable in confirming this supposition. NO2 has been shown (23) to react with dissolved S(IV), but the details of the mechanism and rate of this reaction remain to be elucidated. 

Sulfur dioxide (SO ) and nitrogen oxides (NO ) are oxidized to sulfate and nitrate aerosols either homogeneously rn the gas phase or heterogeneously in atmospheric microdroplets and hydrometeors Gas-phase production of nitric acid appears to be the dominant source of aerosol nitrate because the aqueous phase reactions of NO (aq) are slow at the nitrogen oxide partial pressures typically encountered in the atmosphere (5,i5). Conversely, field studies indicate that the relative importance of homogeneous and heterogeneous SO2 oxidation processes depends on a variety of climatological factors such as relative humidity and the intensity of solar radiation (4, -1 ). 

Titanium dioxide suspended in an aqueous solution and irradiated with UV light X = 365 nm) converted benzene to carbon dioxide at a significant rate (Matthews, 1986). Irradiation of benzene in an aqueous solution yields mucondialdehyde. Photolysis of benzene vapor at 1849-2000 A yields ethylene, hydrogen, methane, ethane, toluene, and a polymer resembling cuprene. Other photolysis products reported under different conditions include fulvene, acetylene, substituted trienes (Howard, 1990), phenol, 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, 2,6-dinitro-phenol, nitrobenzene, formic acid, and peroxyacetyl nitrate (Calvert and Pitts, 1966). Under atmospheric conditions, the gas-phase reaction with OH radicals and nitrogen oxides resulted in the formation of phenol and nitrobenzene (Atkinson, 1990). Schwarz and Wasik (1976) reported a fluorescence quantum yield of 5.3 x 10" for benzene in water. 

Nitropyrene was the sole product formed from the gas-phase reaction of pyrene with OH radicals in a NOx atmosphere (Arey et al, 1986). Pyrene adsorbed on glass fiber filters reacted rapidly with N2O5 to form 1-nitropyrene. When pyrene was exposed to nitrogen dioxide, no reaction occurred. However, in the presence of nitric acid, nitrated compounds were produced (Yokley et al, 1985). Ozonation of water containing pyrene (10-200 pg/L) yielded short-chain aliphatic compounds as the major products (Corless et al, 1990). A monochlorinated pyrene was the major product formed during the chlorination of pyrene in aqueous solutions. At pH 4, the reported half-lives at chlorine concentrations of 0.6 and 10 mg/L were 8.8 and <0.2 h, respectively (Mori et al, 1991). 

Chemical/Physical. Under atmospheric conditions, the gas-phase reaction with OH radicals and nitrogen oxides resulted in the formation of p-tolualdehyde (Atkinson, 1990). Kanno et al. (1982) studied the aqueous reaction of p-xylene and other aromatic hydrocarbons (benzene, toluene, o-and /n-xylene, and naphthalene) with hypochlorous acid in the presence of ammonium ion. They reported that the aromatic ring was not chlorinated as expected but was cleaved by chloramine forming cyanogen chloride. The amount of cyanogen chloride formed increased at lower pHs (Kanno et al, 1982). Products identified from the OH radical-initiated reaction of p-xylene in the presence of nitrogen dioxide were 3-hexene-2,5-dione, p-tolualdehyde, and 2,5-dimethylphenol (Bethel et al., 2000). 

The choice of an appropriate model is heavily dependent on the intended application. In particular, the science of the model must match the pollutant(s) of concern. If the pollutant of concern is fine PM, the model chemistry must be able to handle reactions of nitrogen oxides (NOx), sulphur dioxide (SO2), volatile organic compounds (VOC), ammonia, etc. Reactions in both the gas and aqueous phases must be included, and preferably also heterogeneous reactions taking place on the surfaces of particles. Apart from correct treatment of transport and diffusion, the formation and growth of particles must be included, and the model must be able to track the evolution of particle mass as a function of size. The ability to treat deposition of pollutants to the surface of the earth by both wet and dry processes is also required. 

Large free volume per unit total volume. This property is particularly important if time must be available for a gas-phase chemical reaction, such as the oxidation of nitric oxide in the aqueous absorption of nitrogen dioxide. 

In the specific case of emissions of sulphur dioxide and oxides of nitrogen, the change in oxidizing nature of the atmosphere subsequent to chemical reactions in the atmosphere, and upon deposition, results in changes in the acid base and redox equilibria in the aqueous phases. 

Nitrogen dioxide has limited water solubility and its resulting low aqueous-phase concentration suggests that the reaction... 

The photolysis of nitrate and nitrite in sea water produces nitrogen dioxide (NO2) and nitric oxide (NO), respectively (eqns [I] and [II]). Previous work indicated that the photolysis of nitrite could act as a small net source of NO to the marine atmosphere under some conditions. However, this conclusion seems to be at odds with estimates of the steady-state concentrations of superoxide and the now known rate constant for the reaction of superoxide with nitric oxide (6.7 x 10 M s ) to form peroxyni-trite in aqueous phases (eqn [V]). 

Reaction (4) is of vital importance since the ions produced may enhance the metal dissolution process (Sect. 3.1.2.2.3). When oxidants, such as nitrogen dioxide or ozone, dissolve into the aqueous phase, the bisulfite ion oxidizes to bisulfate (HS04 ), for example,... 

To a solution of propynyl alcohol 48 (0.80 g, 2.7 mmol) in anhydrous dichloromethane (12 mL), under an atmosphere of nitrogen, was added octacarbonyldicobalt (1.02 g, 3.0 mmol) and the reaction was stirred at ambient temperature. The progress of the reaction was monitored by observing the evolution of carbon monoxide from the reaction mixture. TLC analysis, after fifteen minutes, showed the presence of a faster moving compound ( fO.45, 2 1 hexane diethyl ether). The reaction mixture was then cooled to -10 °C whereupon tetrafluoroboric acid diethyl ether complex (0.52 mL, 3.0 mmol, 85% by volume) was added and the mixture left to stir. TLC analysis, after five minutes, showed the presence of a new compound (R( 0.65, 2 1 hexane diethyl ether). To the reaction mixture, maintained at -10 °C, was added dropwise methanolic ceric ammonium nitrate (CAN, 6.67 g, 12.20 mmol, 30 mL) until the evolution of carbon dioxide ceased and the yellow color of CAN persisted (about fifteen minutes). TLC analysis of the reaction mixture revealed the presence of a new compound (/ f 0.40, 3 1 hexane diethyl ether). Residual methanol was removed in vacuo and the residue was partitioned between diethyl ether (25 mL) and water (25 mL). The aqueous phase was extracted with diethyl ether ( 3 x 20 mL) and the combined organic extracts were dried over anhydrous magnesium sulfate, filtered, and the solvent removed in vacuo to afford an oil. Purification was effected by column chromatography on silica (3 1 hexane diethyl ether) to afford the desired compound 49 (0.53 g, 66%) as a yellow oil. 

Carbon dioxide gas diluted with nitrogen is passed continuously across the surface of an agitated aqueous lime solution. Clouds of crystals first appear just beneath the gas-liquid interface, although soon disperse into the bulk liquid phase. This indicates that crystallization occurs predominantly at the gas-liquid interface due to the localized high supersaturation produced by the mass transfer limited chemical reaction. The transient mean size of crystals obtained as a function of agitation rate is shown in Figure 8.16. 

Foams may be prepared by either one of two fundamental methods. In one method, a gas such as air or nitrogen is dispersed in a continuous liquid phase (e.g. an aqueous latex) to yield a colloidal system with the gas as the dispersed phase. In the second method, the gas is generated within the liquid phase and appears as separate bubbles dispersed in the liquid phase. The gas can be the result of a specific gasgenerating reaction such as the formation of carbon dioxide when isocyanate reacts with water in the formation of water-blown flexible or rigid urethane foams. Gas can also be generated by volatilization of a low-boiling solvent (e.g. trichlorofluoromethane, F-11, or methylene chloride) in the dispersed phase when an exothermic reaction takes places, (e.g. the formation of F-11 or methylene chloride-blown foams). 

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