Molecular marker-based source apportionment of PM_2.5-Associated organic compounds in a transboundary-influenced...

This study investigates the sources and seasonal dynamics of organic aerosol (OA) in a medium-sized urban receptor region characterized by limited major point sources, relatively low overall anthropogenic emission intensity, and significant susceptibility to regional impacts. Molecular marker analysis of n-alkanes, polycyclic aromatic hydrocarbons (PAHs), dicarboxylic acids (DCAs), fatty acids, anhydrosugars, and secondary organic aerosol (SOA) tracers was integrated with dispersion-normalized positive matrix factorization (DN-PMF) and concentration-weighted trajectory (CWT) analysis. DN-PMF resolved seven OA factors and revealed a clear seasonal transition between distinct atmospheric control regimes. During the heating period, OA was dominated by primary combustion-related factors, with biomass-burning OA (BBOA) and coal-combustion OA (CCOA) contributing 36% and 19%, respectively, together with enhanced traffic contribution. In contrast, the non-heating period was dominated by Aged OA (56%), while cooking OA (21%) and tracer-defined SOA (12%) became relatively more important. These results indicate that heating-period OA was governed mainly by the accumulation of multi-source primary emissions under stagnant conditions, whereas non-heating-period OA was shaped more strongly by photochemical production, atmospheric aging, and regional processing. Notably, the non-heating-period OA burden was influenced more by regionally processed and atmospherically aged organic material than by relatively fresh tracer-defined SOA alone. The results suggest that OA variability in receptor regions is controlled not only by local emissions and transport, but also by the extent of atmospheric processing, implying that effective mitigation requires coordinated management of both primary emissions and regional precursor sources.