Radical-Omics Reveals the Hydrogen-Abstraction Pathway of Isoprene Oxidation

Isoprene is the most abundant biogenic volatile organic compounds (BVOCs) and has far-reaching impacts on secondary organic aerosol (SOA) formation globally 1-6. Atmospheric oxidation of isoprene produces a diverse range of isomeric radicals that drive subsequent chain propagation and mechanistic branching 7-10. However, no high-throughput experimental characterization of isomeric-resolved radicals of isoprene is available, leaving critical gaps in our understanding of the underlying molecular mechanisms. Here we establish a radical-omics approach that enables isomer-specific identification and detection of hundreds of radical species generated in the VOCs oxidation system. Applied to the OH-initiated reaction of isoprene, four OH-added allylic radicals were experimentally quantified to derive their branching ratios. In addition, hydrogen-abstraction was found to be an unexpectedly important pathway, contributing up to 8.80 ± 3.21% of the total branching. Incorporating the updated mechanism into a global chemical transport model shows that this pathway contributes up to 13.5% of the total isoprene-derived low-volatility SOA over tropical rainforests. Our findings provide a missing experimental foundation for isoprene chemistry via the combination of radical screening with targeted mechanistic validation, thereby revealing hidden reaction pathways under complex atmospheric conditions.