Highly oxidized products from the atmospheric reaction of hydroxyl radicals with isoprene

Abstract Isoprene (C 5 H 8 ) globally accounts for half of the non-methane hydrocarbon flux into Earth´s atmosphere. Its degradation is mainly initiated by the gas-phase reaction with OH radicals yielding a complex system of RO 2 radicals. Subsequent product formation is not conclusively understood yet. Here we report the observation of C 4 - and C 5 -products from OH + isoprene bearing at least two functional groups. Their production is initiated either by the reaction of initially formed δ-RO 2 radicals with NO or by 1,6 H-shift isomerization of Z -δ-RO 2 radicals. Both reaction channels also form highly oxygenated molecules (HOMs), which could be important for the generation of secondary organic aerosol. C 5 H 9 O 8 and C 5 H 9 O 9 radicals represent the main precursors of closed-shell HOMs. Global simulations revealed that the isoprene-derived HOM-RO 2 production is comparable with that of α-pinene, currently regarded as very important HOM source. This study provides a more complete insight into isoprene´s degradation process including the HOM formation.