Abstract
This study characterizes wintertime volatile organic compound (VOC) emissions, oxidative aging, and secondary organic aerosol (SOA) formation in Seoul using high-resolution, real-time measurements. Anthropogenic VOCs, particularly BTEX, dominated emissions under stagnant meteorological conditions with shallow boundary layers. Two hydrocarbon photochemical clocks provided complementary aging metrics: the reactive [benzene]/[TMB] ratio captured fresh, rapidly oxidized local air masses, while the slower [benzene]/[toluene] ratio reflected aged, regionally transported air─with distinct diurnal patterns confirming this dual character. SOA/OA ratios correlated more strongly with OH exposure (OHexp) from the [benzene]/[TMB] clock, highlighting short-lived aromatics as key local SOA drivers. Compositional analysis revealed a sequential SOA evolution continuum: rapid initial formation of less-oxidized OA (LO-OOA) followed by progressive aging into more-oxidized OA (MO-OOA). A semiempirical volatility basis set (VBS) model reproduced observed SOA temporal trends (R2 = 0.53–0.58), capturing 50–60% of ambient SOA mass from measured precursors alone─driven by cold winter temperatures and abundant reactive aromatics. Systematic underestimation during peak pollution events highlights the need to explicitly account for intermediate-volatility organic compounds (IVOCs) from cold-start emissions and multigenerational aging mechanisms to close the wintertime urban SOA mass gap.