In this study, PM_2.5 samples collected between October 29 and December 23, 2018 at a roadway site in Gwangju, Korea, were comprehensively characterized by chemical, optical, and spectroscopic methods. Aerosol light absorption was observed with a time resolution of 1 min using a dual-spot aethalometer. An Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy analysis was also applied to characterize organic and inorganic components in the PM_2.5 samples. Three PM_2.5 pollution episodes which exceeded the 24-hr Korean PM_2.5 standard (35 μg/m³) were classified; Episode I was associated with local air stagnation and long-range transportation of aerosol particles from northeast China and upwind regions; Episode II was affected by Asian dust (AD) particles and local pollution under low relative humidity (RH) conditions; and Episode III was strongly associated with accumulation of local pollution due to very high RH and low wind speed, along with regional transport of aerosol particles from eastern China.

The contribution of organic aerosols to PM_2.5 was higher during episodes I and II than during episode III, while the contribution of NO₃⁻ particles was greater during episode III, possibly due to very high RH and low wind speed conditions. Unexpectedly, SO₄²⁻ was not an important component of PM_2.5 during the three episodes. The light absorption coefficient (b_BrC,370) of brown carbon (BrC) at 370 nm was estimated to range from 9 Mm⁻¹ during episode II to 14 Mm⁻¹ during episode III, but the contribution of b_BrC,370 to total aerosol absorption was the lowest during episode III. Multiple linear regression analysis indicated that the contributions of the traffic emissions, biomass burning (BB) emissions, and secondary formation processes to b_BrC,370 absorption were, on average, 37, 39, and 14% of the total estimated b_BrC,370, respectively, suggesting that primary traffic emissions are an important contributor to BrC absorption at the roadway site. ATR-FTIR analysis showed that aliphatic carbon group (C–H), carbonyl group (CO), ammonium, sulfate, and nitrate were identified in all filter samples collected during the three pollution episodes; the corresponding bands had the highest intensities in the filter sample from episode III. However, the presence of mineral dusts related to hydroxyl group (-OH), gypsum, Al–Al–OH group, CO₃²⁻, and SO₃²⁻ were clearly detected at the absorbance bands at 3400–3700 and 650–900 cm⁻¹ in the AD sample only (episode II). Furthermore, the absorbance bands observed at 2910 and 2850 cm⁻¹ during the pollution episodes were assigned to methylene groups (–CH₂–), which are associated with BB emissions, and the intensities of those bands during pollution episodes were consistent with the concentrations of BB indicators (e.g., levoglucosan and K⁺). These FTIR method can provide valuable chemical insights into the nature of the organic and inorganic components present in ambient aerosol particles during different pollution episodes.