Ci

I 02

FIGURE 13.24 Summary of major tropospheric reactions of HCFC-141b.

dominates over decomposition by C-C bond scission (Edney et al., 1991; Tuazon and Atkinson, 1993b, 1994):

OCH2CFCl2

HCHO + CFCL

FIGURE 13.23 Summary of major tropospheric reactions of HCFC-123.

Further reaction of CFC12 with 02 and subsequently with NO generates C1C(0)F.

Figure 13.24 summarizes the chemistry of HCFC-141b.

In short, the tropospheric chemistry of the CFC replacement compounds containing abstractable hydrogen atoms is very similar to the VOC chemistry discussed in Chapter 6. The major differences are found in the relative importance of the various potential fates of the alkoxy radicals formed in these reactions, which depends on the structure of the parent compound. Table 13.7 summarizes the major and minor products formed by the tropospheric oxidation of the four particular typical CFC replacement compounds treated here. For the chemistry of other CFC replacements, see papers by Chen et al. (1997) and a series of papers by Wallington, Nielsen, and co-workers (e.g., Wallington et al., I994a; Wallington and Nielsen, f 995; M0gel-berg et al., 1995a, f995b, f995c, 1996, 1997; Giessing et al., 1996). The atmospheric chemistry of a series of hydrofluoroethers (HFE), such as C4F9OCH3 (HFE-7100), C4F904C2H5 (HFE-7200), and CF3CH20CH2CF3, used as CFC alternates is discussed by Wallington et al. (1997, 1998), Christensen et al. (1998), and Cavalli et al. (1998)

e. Tropospheric Fates of Halogenated Products of HCFC Oxidation

As seen in Table 13.7, oxidation of HCFCs by OH generates a variety of halogenated aldehydes and ketones as well as phosgene (COCl2), its fluorine analog (COF2), C1C(0)F and HC(0)F, and the alcohol CF3OH. The ultimate atmospheric fate of these products depends on their structures, of course, which determines their absorption cross sections as well as reactivity with OH, and their solubility in aqueous solutions such as clouds, rainwater, and the oceans.

TABLE 13.7 Typical Organic Products of the Tropospheric Oxidation of Some of the CFC Replacement Compounds

Replacement Compound

Major fates of alkoxy radicals

Major products

Minor products

HFC-134a

0 0

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