Uptake into and Reaction with Liquid Water

It is known from studies carried out over many decades that oxides of nitrogen at high concentrations dissolve in aqueous solution and react to form species such as nitrate and nitrite. With the focus on acid deposition and the chemistry leading to the formation of nitric and sulfuric acids during the 1970s and 1980s, a great deal of research was carried out on these reactions at much lower concentrations relevant to atmospheric conditions (for reviews, see Schwartz and White, 1981, 1983 and Schwartz, 1984). 

Through these studies, it was concluded that absorption of NO and N02 into the aqueous phase in the form of clouds and fogs in the atmosphere and their subsequent oxidation are not significant under typical atmospheric conditions. The major reasons for this are that NO and N02 are not highly soluble and, in addition, the reactions are kinetically rather slow due to the dependence of the rates on the square of the reactant concentration. As a result, like the oxidation of NO by 02, the reactions slow down dramatically when the 

FIGURE 7.4 Processes involved in uptake of NO and N02 into the aqueous phase in fogs and clouds and subsequent oxidation. 

To put the values in Table 7.1 in perspective, highly soluble gases have Henry s law constants of the order of 10s and relatively insoluble gases have values of 

TABLE 7.1 Some Rate and Equilibrium Constants of Aqueous-Phase Reactions of NO and NOza 

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