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

Isoprene (C₅H₈) 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 RO₂ radicals. Subsequent product formation is not conclusively understood yet. Here we report the observation of C₄- and C₅-products from OH + isoprene bearing at least two functional groups. Their production is initiated either by the reaction of initially formed δ-RO₂ radicals with NO or by 1,6 H-shift isomerization of Z-δ-RO₂ radicals. Both reaction channels also form highly oxygenated molecules (HOMs), which could be important for the generation of secondary organic aerosol. C₅H₉O₈ and C₅H₉O₉ radicals represent the main precursors of closed-shell HOMs. Global simulations revealed that the isoprene-derived HOM-RO₂ 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.