FIGURE 7.f6 Model-predicted fraction of HNO, (/,,NOl) produced by heterogeneous N205 and NO, hydrolysis in January (adapted from Dentener and Crutzen, 1993).

I Jun

FIGURE 7.17 Model-predicted ratio, R(u, of 03 concentrations with aerosol reactions included those without for all months (adapted from Dentener and Crutzen, 1993).

Furthermore, because these reactions result in the effective removal of NOx from ozone production, by removing N02, the model also predicts that 03 concentrations will decrease. Figure 7.17, for example, shows the model results for the ratio of 03 (R0 ) with the heterogeneous removal of N03 and N205 included to that without these aerosol reactions. In some locations, the 03 concentrations are predicted to be as much as 30% lower than they would have been in the absence of the heterogeneous reactions. Because 03 is also the major OH source on a global scale, via its photolysis to electronically excited oxygen atoms, Of'D), which react in part with gas-phase water, this also decreases the predicted OH levels.

In urban airsheds, the hydrolysis of N205 and N03 can be even more important as a source of HN03 due to their higher concentrations in more polluted regions.

The implications of reaction (47) in the stratosphere are discussed in detail in Chapter 12. However, suffice it to say that it also plays a critical role in that region of the atmosphere as well.

b. Other Reactions

While the hydrolysis of N2Os is believed to represent its major loss process, there are other possibilities that have potentially interesting implications under certain conditions. For example, N2Os reacts with the components of sea salt particles such as NaCl, NaBr, and Nal to form nitryl chloride, nitryl bromide, and nitryl iodide, respectively (e.g., Finlayson-Pitts et al., 1989a, 1989b; Behnke and Zetzsch, 1990; Zetzsch and Behnke, 1992; Junkermann and Ibusuki, 1992; George et al., 1994; Behnke et al., 1994, 1997; Leu et al., 1995; Fenter et al., 1996; Barnes et al., 1991; Schweitzer et al., 1998):

NaBr(s,aq) + N205(g) BrN02(g) + NaN03(s), (50) Nal( + N205(g) - IN02(g) + NaN03(s). (51)

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