Isoprene, alpha-pinene, and beta-pinene are emitted mainly from biogenic sources and play important roles in determining the oxidative chemistry of the troposphere. The ozonolysis reactions of these alkenes are investigated using vacuum ultraviolet (VUV) photoionization mass spectrometry.  To detect the early reactive intermediates and characterize the initial steps of ozonolysis of isoprene and pinenes, the ozonolysis reactions are carried out in a fast flow reactor in a short reaction time of 50-200 ms under low pressure (8-40 Torr).  CO is used as an OH scavenger to reduce the reactions between the OH byproduct and alkenes. After the short reaction time, the initial products, both free radical intermediates and stable species, are sampled into a molecular beam and directly detected by tunable synchrotron photoionization mass spectrometry.  Mass and photoionization efficiency spectra of the initial products are obtained and theoretical calculations are also carried out to identify the products.  New reaction pathways of the ozonolysis of these alkenes are observed, and the reaction mechanisms will be discussed.

Mass spectrometry and theoretical study of early intermediates in ozonolysis of atmospherically important alkenes

244th National Meeting (2012)

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