For a comprehensive evaluation of the key factors determining the oxidative potential (OP) of PM_2.5, 75 samples of PM_2.5 were collected in urban Seoul, South Korea, during 2019-2021, and dithiothreitol consumption (DTTv) was measured using a DTT assay, coupled with an analysis of major constituents and stable isotope ratios of PM_2.5. For the entire sample set, the mean DTTv value was 0.58 ± 0.48 nmol m^-3 min^-1 for PM_2.5 of 29.1 ± 12.2. DTTv exhibited a general dependence on of PM_2.5 concentrations and major constituents, including NO₄⁺, SO₄^2-, NH₄⁺, and organic carbon (OC). Specifically, NO₃^- and NH₄⁺ demonstrated the most robust correlation with DTTv during the cold season, whereas only elemental carbon (EC) showed a significant correlation with DTTv in the warm season. The δ¹³C of total carbon (TC) and δ¹⁵N of total nitrogen (TN) displayed an inverse correlation concerning DTT activities, suggesting the significant contribution from solid fossil fuels and biomass burning to the oxidative potential of PM_2.5, particularly during the cold season when PM_2.5 was notably high. In contrast, vehicle emissions were found to influence DTTv even at low PM_2.5 levels in warm seasons. This study provides insights into the intricate dynamics influencing the oxidative potential of PM_2.5.

Black carbon emitted by incomplete combustion of fossil fuels and biomass has a net warming effect in the atmosphere and reduces the albedo when deposited on ice and snow; accurate knowledge of past emissions is essential to quantify and model associated global climate forcing. Although bottom-up inventories provide historical Black Carbon emission estimates that are widely used in Earth System Models, they are poorly constrained by observations prior to the late 20th century. Here we use an objective inversion technique based on detailed atmospheric transport and deposition modeling to reconstruct 1850 to 2000 emissions from thirteen Northern Hemisphere ice-core records. We find substantial discrepancies between reconstructed Black Carbon emissions and existing bottom-up inventories which do not fully capture the complex spatial-temporal emission patterns. Our findings imply changes to existing historical Black Carbon radiative forcing estimates are necessary, with potential implications for observation-constrained climate sensitivity.