The oxidative potential of secondary organic aerosol (SOA) was measured by dithiothreitol assay. To quantify the reactive functional groups of particulate oxidizers that can increase dithiothreitol response, the quantities of quinones, organic hydroperoxides, and peroxy acyl nitrates were measured by chemical assays. Organic hydroperoxides were largely attributed to the oxidative potential of SOA. The results provide a deep understanding of the mechanistic role of SOA in modifying biomolecules.