Nitric oxide aqueous phase reactions

There are well over 100 gaseous and aqueous phase reactions that can lead to acid formation and more than fifty oxidizing agents and catalysts may be involved. However, in the simplest terms sulfur in fuels is oxidized to SO2, and SO2 in the atmosphere is further oxidized and hydrolyzed to sulfuric acid. Most nitric acid is formed by the fixation of atmospheric nitrogen gas (N2) to NO. (NO and NO2) during high temperature combustion, followed by further oxidation and hydrolysis that produces nitric acid in the atmosphere. These materials can be dry-... 

Techniques are at hand to evaluate the rates of aqueous-phase acid formation reactions in clouds. Such evaluations indicate that oxidation of SO2 by H2O2 and O3 can be important in-cloud reactions for assumed representative reagent concentrations and other conditions. Rapid aqueous-phase reactions do not appear to be indicated for oxidation of nitrogen oxides to nitric acid. 

Extrapolation to the K/T boundary requires consideration of the time scales of acid deposition. Nitric acid formation occurs rapidly by aqueous phase reaction of NO and NO2 with liquid water produced by tlie incident K/T bolide on both impact and infall of ejecta. For tlie quantities of NO produced by the K/T impact ( 10 5 moles), conversion to HNO3 occurred wiUiin days, assuming sufficient liquid water was available in the posl-K/T atmosphere. The nitric acid will form an acid rain of pH 0 for a liquid water content of 1 g/m (typical of tropospheric clouds) but will contain enough protons to weather only 3 x 10 moles of Sr, for Sr/(Ta -0.003 in soil and bedrock minerals. Sulfuric acid formation occurred on a time scale of years [7] due to the slow rate of gas phase SO2 oxidation. Spread evenly over 10 years, 10 moles of SO2 produced a global acid rain of pH —4, and released —3 x 10 moles of Sr. 

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 ). 

The notion that chemical reactions in the aqueous phase may be important to atmospheric chemistry dates back at least 30 yr, when Junge and Ryan (1958) called attention to the great potential of cloud water for the oxidation of dissolved S02 by heavy-metal catalysis. At that time the process appeared to be the only viable oxidation mechanism for atmospheric S02. Later, when the concept of OH radical reactions gained ground, the gas-phase oxidation of S02 by OH was recognized to be equally important. The recent revival of interest in aqueous phase reactions is connected with efforts to achieve a better understanding of the origins of rainwater acidity. An oxidation of N02 to nitric acid also takes place in cloud water. Contrary to previous ideas, however, this process was recently shown to have little influence on atmospheric reactions of N02. 

Physical properties of hexachloroethane are Hsted in Table 11. Hexachloroethane is thermally cracked in the gaseous phase at 400—500°C to give tetrachloroethylene, carbon tetrachloride, and chlorine (140). The thermal decomposition may occur by means of radical-chain mechanism involving -C,C1 -C1, or CCl radicals. The decomposition is inhibited by traces of nitric oxide. Powdered 2inc reacts violentiy with hexachloroethane in alcohoHc solutions to give the metal chloride and tetrachloroethylene aluminum gives a less violent reaction (141). Hexachloroethane is unreactive with aqueous alkali and acid at moderate temperatures. However, when heated with soHd caustic above 200°C or with alcohoHc alkaHs at 100°C, decomposition to oxaHc acid takes place. 

The oxidation of primary and secondary alcohols by stable organic nitroxyl radicals has been reviewed.111 The kinetics of reactions of alkanes and arenes with peroxynitrous acid suggest the participation of the same active oxidizing species in both gas and aqueous phase HOONO or its decomposition product OONO. 112 The oxidation of the alkaloids reserpine and rescinnamine by nitric acid has been studied.113... 

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. 

Nitrous and nitric acids are produced in the aqueous phase after NO2 and/or N2O3 are absorbed into solution and sulfur oxyacids, such as sulfite/bisulfite or pyrosulfite, are formed if SO2 dissolves in the solution. Interaction among oxides of nitrogen, nitrogen oxyacids, sulfur oxyacids, oxygen, and trace metal ions such as Fe(III) or Mn(II) can take place in a flue gas wet scrubber. Identifying all reactions involved in this complex system is impossible. However, important reactions must be identified and characterized in order to improve the performance of a scrubber. 

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]). 

Use of sensors to measure gas phase NO2 concentration, electrical conductivity of the reaction mass, and gas phase temperatures at several critical points in semi-continuous nitration reactors permits safe operation of nitration processes [10]. The use of non-aqueous titration analysis in the control of nitration processes in explosives manufacture is discussed [11]. Counter-intuitively, safety of spent acids from nitrate ester production is decreased by lowered nitric acid content. This is because the runaway reaction is oxidation of alcohols, kinetically easier than that of the dissolved nitrate esters from which the alcohols are reformed by hydrolysis [16]. 

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