Source apportionment and dynamics of PM2.5 across regions during and after the coronavirus 2019 pandemic.

The coronavirus disease 2019 (COVID-19) pandemic was reported to improve air quality. However, the effects of lockdown on PM₂.₅ and its chemical components based on source-specific characteristics remain unclear. This study evaluated and compared the components of PM₂.₅ across three target sites-Seoul, Ansan-Siheung, and Wonju-based on source distribution patterns during the pandemic and post-pandemic periods. The results revealed that total ion concentrations decreased by 7-19% at the target sites, while trace element concentrations increased by 19-29% in the post-pandemic period. Carbon concentrations showed region-specific trends. Components associated with secondary formation, such as SO₄²⁻, NO₃⁻, and NH₄⁺, decreased, whereas natural-origin components, such as Cl⁻, Na⁺, Mg²⁺, and Ca²⁺, increased, indicating enhanced dust resuspension. Furthermore, a positive matrix factorization (PMF) analysis demonstrated a predominance of primary emission sources and resuspended dust in the post-pandemic period, with a decline in contributions from secondary formation sources. These regional variations were primarily influenced by the extent of socioeconomic activities, with Seoul exhibiting a higher contribution from primary emissions and suspended dust. This study emphasizes the importance of establishing region-specific air quality improvement policies by scientifically identifying the impacts of anthropogenic activity on PM₂.₅ components and their sources.