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

Abstract

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 PM2.5 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 EMAC, was calculated based on the change in MAC. The campaign-averaged EMAC 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 EMAC, with the most significant correlation between OC/EC and EMAC, 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 EMAC revealed the contribution of biomass burning.