It is interesting that the reactions of a-terpinene and a-phellandrene with N03 also gave the corresponding aromatic, p-cymene, in significant yields (6 and 22%, respectively), suggesting an additional path producing N02 + H20 + aromatic (Berndt et al., 1996).
Since 2-methyl-3-buten-2-ol is now recognized as being emitted in significant quantities, its kinetics and mechanisms of oxidation are also of interest. Reaction with OH is fast, with the rate constant reported to be in the range of (4-7) X 10"" cm3 molecule-1 s_l (Rudich et al., 1995; Fantechi et al., 1998a; Ferranto et al., 1998). As expected, the reaction proceeds primarily by addition to the double bond. The major products of the reaction in air are CHOCH2OH (glycoaldehyde), acetone, and HCHO (Grosjean and Grosjean, 1995; Fantechi et al., 1998b; Ferranto et al., 1998) (see Problem 12).
2-Methyl-3-buten-2-ol also reacts with 03 and N03, with the rate constants for these reactions being 1 x spectively (Grosjean and Grosjean, 1994; Rudich et al., 1996; Hallquist et al., 1996; Fantechi et al., 1998a). Major products of the 03 reaction have been reported to be acetone, HCHO, HCOOH, and possibly 2-hydroxy-2-methylpropanal. Major products of the N03 reaction are acetone and organic nitrates, peroxy nitrates, and carbonyl nitrates (e.g., Fantechi et al., 1998b). These are consistent with the mechanisms of reaction of 03 and NO-, discussed earlier in this chapter.
As anticipated from their structures, the products formed from the initial reactions of the biogenics (Table 6.26) are also highly reactive with OH, 03, and N03. For example, the rate constants (Alvarado et al., 1998a) for the reaction of pinonaldehyde with OH, 03, and NO-, are 4.8 x f0"1< 2 x 10"2°, and 2 x 10"i4 cm3 molecule"1 s"1, respectively (see also Glasius et al., 1997; and Hallquist et al., 1997), leading to a lifetime of ~6 h with respect to the OH reaction (at an [OH] of 1 x 106 radicals cm"3) and ~11 h with respect to the reaction with 50 ppt N03. Photolysis is also important, with a photolysis lifetime of ~ 3 h for 50°N on July f, assuming a quantum yield of one (Hallquist et al., 1997).
Again, the reaction products are complex. For example, the N03 reaction has been reported to give 3-acetyl-2,2-dimethylcyclobutane acetylperoxynitrate (Wangberg et al., 1997; Noziere and Barnes, 1998):
A review of the gas-phase oxidation products is given by Calogirou et al. (1999).
The chemistry of dimethyl sulfide, a major biogenic in marine areas, is discussed in Chapter 8.E.I.
b. General Remote Boundary Layer Chemistry
The most universal characteristic of remote regions compared to those clearly subject to anthropogenic influences is the low NOx (see Crutzen, 1995, for a review). Under these conditions, OH is generated by the photolysis of 03 to O('D), followed by its reaction with water vapor, which occurs in competition with deactivation to 0(3P):
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