Water-soluble organic matter (WSOC) and metals in atmospheric particulate matter are components that contribute to free radicals significantly, but their formation mechanism is not well understood. In this study, electron paramagnetic resonance spectroscopy (EPR) combined with free radical capture (BMPO/DMPO) technology was used to explore the interaction between WSOC and metal on radical formation. The results showed that the free radicals generated by the reaction of four typical WSOCs (salicylic acid, malonic acid, phthalic acid, catechol) with Fe2
were consistent with the free radicals generated by BMPO extract of PM2.5
. Furthermore, through liquid phase reaction of WSOC with Fe2
, it was found that alkyl or aromatic radicals were formed from Fe2
with WSOC, while Fe3
promoted the formation of hydroxyl radicals, alkoxy radicals, hydroperoxide radicals, alkyl radicals, indicating that the free radical’s formation mechanism by Fe2
was different. Subsequently, liquid-solid reaction of four catechols substances with the Fe-loaded mineral particles was conducted and environmentally persistent free radicals (EPFRs) were obtained and no transient radical formation was detected, which indicates that non-free metals and WSOCs can generate EPFRs, while free metals can generate transient free radicals.