[Aerosol Optical Properties and Light Absorption Enhancement of EC During Wintertime in Nanjing]

A three-wavelength photoacoustic soot spectrometer (PASS-3) was employed for real-time online measurement of aerosol optical properties and light absorption enhancement of EC together with chemical composition analysis in the northern suburb of Nanjing during January 1-19, 2016. The average aerosol absorption coefficient, scattering coefficient, and single scattering albedo at 532 nm during the observation period were (64.19±35.28) Mm^-1, (454.68±238.71) Mm^-1, and 0.87±0.03, respectively, and showed clear diurnal variation, mainly affected by planetary boundary layer height and PM_2.5 mass concentration. The mass absorption cross section (MAC) showed an increasing trend during the observation period, consistent with the trend of variation in ratios between non-EC and EC components, resulting from the difference in relative percentage of secondary materials and coating thickness under different pollution conditions. The estimated light absorption enhancement, denoted E_MAC, was calculated based on the change in MAC. The campaign-averaged E_MAC at 405, 532, and 781 nm were 1.53±0.56, 1.34±0.47, and 1.14±0.40, respectively, showing a decrease with increasing wavelength, suggesting the contribution of brown carbon (BrC). All non-EC components showed linear correlation with E_MAC, with the most significant correlation between OC/EC and E_MAC, indicating that an increase in organics was likely the main contributor to light absorption enhancement in our study. In addition, the high correlation of K⁺/EC and E_MAC revealed the contribution of biomass burning.