Emission Characteristics of Volatile Organic Compounds and Organic Aerosol Evolution with OH Exposure in Seoul During Winter

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.