Highly Oxidized RO sub( 2) Radicals and Consecutive Products from the Ozonolysis of Three Sesquiterpenes

The formation of highly oxidized multifunctional organic compounds (HOMs) from the ozonolysis of three sesquiterpenes, alpha -cedrene, beta -caryophyllene, and alpha -humulene, was investigated for the first time. Sesquiterpenes contribute 2.4% to the global carbon emission of biogenic volatile organic compounds (BVOCs) and can be responsible for up to 70% of the regional BVOC emissions. HOMs were detected with chemical ionization-atmospheric pressure interface-time-of-flight mass spectrometry and nitrate and acetate ionization. Acetate ions were more sensitive toward highly oxidized RO... radicals containing a single hydroperoxide moiety. Under the chosen reaction conditions, product formation was dominated by highly oxidized RO... radicals which react with NO, NO..., HO..., and other RO... radicals under atmospheric conditions. The ozonolysis of sesquiterpenes resulted in molar HOM yields of 0.6% for alpha -cedrene (acetate), 1.8% for beta -caryophyllene (acetate), and 1.4% for alpha -humulene (nitrate) afflicted with an uncertainty factor of 2. Molar yields of highly oxidized RO... radicals were identical with HOM yields measuring the corresponding closed-shell products. HOM formation from ozonolysis of alpha -cedrene was explained by an autoxidation mechanism initiated by ozone attack at the double bond similar to that found in the ozonolysis of cyclohexene and limonene. (ProQuest: ... denotes formulae/symbols omitted.)