Mass spectrometric investigation of the OH induced oxidation of isoprene using 0 2 + as a chemical ionization reagent

Isoprene (2-methyl-1,3-butadiene) is a dominant non-methane organic compound emitted into the atmosphere by vegetation, with an annual global emission rate of 500 Tg/yr. It represents almost 50% of all biogenic non-methane hydrocarbons on a global scale. It has a substantial impact on troposphere oxidants. The focus of this research is a preliminary investigation of isoprene oxidation reaction, in the presence of OH radicals and high NOx concentrations. An ion-trap time of flight mass spectrometer was used for analysis. It consisted of a source chamber and a flight tube. Main portion of the source chamber contained a quadrupole ion-trap where chemical ionization and ion storage took place. 02 + ions were used as chemical ionization reagent. Sample fragments were stored in the center of the ion-trap where their trajectories were stable, then after a certain period of storage time ejected simultaneously into the flight tube for mass analysis. In order to trap heavier masses, conditions for ion-trap efficiency were improved and to achieve quantitative results, the mass spectrometer was calibrated and calibration spectra were generated for isoprene and its oxidation products. This helped in calculating concentrations, as a function of time, for reactants and products of isoprene oxidation. The percentage yields of the products (methacrolein and methyl vinyl ketone) were also determined.