Formation of HONO

As already discussed, a major source of HONO is believed to be heterogeneous reactions of NOz, includ

Time (PST)

FIGURE 7.8 Calculated rates of formation of OH radical from photolysis of HONO, 03, and HCHO at Long Beach, California, on December fO, 1987 (adapted from Winer and Biermann, f994).

ing that with water adsorbed on various surfaces and with reactive sites on the surface of soot. During the day, it can also be formed by the reaction of OH with NO:

This termolecular reaction is in the falloff region between second and third order at 1 atm pressure and 298 K. It has a low-pressure limiting rate constant of k{) = 7.0 X 10"31 cm6 molecule-2 s~' and a high-pressure limiting rate constant of k^ = 3.6 X 10"" cm3 molecule"1 s"1 at 300 K (DeMore et al., 1997). Since most OH sources require photolysis of some precursor, this reaction would be expected to be most important during the daylight hours. However, because HONO photolyzes so rapidly during the day, significant concentrations are not generated (see Problem 6).

Zhu and co-workers (1993) observed the formation of HONO in an environmental chamber during the decay of peroxynitric acid, H02N02, and suggested that H02N02, formed in the HOz + N02 reaction,

reacted heterogeneously on the walls of the reactor to form HONO:

Figure 7.9, for example, shows the decay of H02N02 and the formation of HONO and HNO, in their chamber. The peroxynitric acid was generated by reaction (27), where the H02 was formed by the bromine atom initiated oxidation of formaldehyde in air. Zhu et al.

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