Gas-Phase Ozone Oxidation of Monoterpenes: Gaseous and ...

252 JIANZHEN YU ET AL.
Figure 14. Reaction mechanism of O 3 /β-pinene reaction.
to form an acetyl-like radical I 1 and I 2 . For the acetyl radical, it has been established
that its subsequent reactions with O 2 and HO 2 radical lead to the formation of acetic
acid (Niki et al., 1985; Moortgat et al., 1989).
Similarly, the reaction of I 1 and I 2 with O 2 , and subsequently with HO 2 would
lead to P 6 .I 2 can also lose a molecule of CO to form I 3 , which reacts with O 2 ,
and a peroxy radical RO 2 to form I 4 . It follows that I 4 loses one H-atom to an O 2
molecule to produce P 10 . The formation of P 5 , norpinic acid (P 1 ), and pinic acid
(P 2 ) is presupposed to result from oxidation of their corresponding aldehydes, P 10 ,
P 5 and P 6 , respectively, although the explicit oxidation mechanism is unclear.
The formation pathway for a possible candidate of P 8 is proposed to arise
from I 5 , which can be formed from isomerization of I 1 . It is difficult to construct
plausible formation pathways for pinonic acid and hydroxy pinonic acid.