Fenton oxidation of gaseous isoprene nonaqueous aerosol surfaces

Abstract

We report that gas-phase isoprene ISO(g) is oxidized upon impacting the surface of aq. FeCl_2 solns. simultaneously exposed to H_2O_2(g). Expts. involve exposing microjets of micromolar FeCl_2 solns. at pH < 4 to ISO(g) + H_2O_2(g) mixts. for ∼ 10 μs within the spraying chamber of an electrospray ionization mass spectrometer (ESI-MS). Products are analyzed online in the pos. and neg. ion modes. We detect protonated monomer and oligomer species (ISO)_(1-8)H+, in accord with our previous report (J. Chem. A, 116 2012 6027), plus myriad (m/z) > 150 oxidn. products whose combined yields amt. to ∼ 5% of (ISO)_(1-8)H+. MS/MS anal. reveals that pos. ions typically split H_2O and O neutrals, whereas the less abundant neg. ions undergo CO, H_2O and CO_2 losses. All products are inhibited by the addn. of excess t-butanol to FeCl_2 solns. as ×OH scavenger. These results implicate an oxidn. process initiated by the addn. of interfacial OH and/or HO_2 to ISO leading to poly-alcs., carbonyls, hydroperoxides and carboxylic acids. We infer that gaseous olefins can be oxidized upon impacting the surface of Fe-contg. aq. environmental surfaces, including those of aerosols.