[Optical Absorption Properties of Brown Carbon Aerosols in Guangzhou]

In this work, we conducted measurements using a seven-wavelength aethalometer, an online OCEC analyzer, and a MARGA to investigate brown carbon (BrC) absorption properties and source origins during the winter of 2014 at Panyu station, Guangzhou. The results showed that the average absorption contributions of BrC decreased with an increase in wavelength, measured as 25.9%, 19.7%, 14.1%, 11.6%, and 7.7% at 370 nm, 470 nm, 520 nm, 590 nm, and 660 nm, respectively. Diurnal variations in BrC absorption and the concentrations of potassium cations (K⁺) and organic carbon (OC) was high at night and low during the day, which was attributed to biomass burning. This indicated that BrC was emitted from straw burning in rural areas and accumulated in the steady planetary boundary layer at night. Diurnal variations in the ratio of BrC absorption to OC concentrations showed a distinct dip during the afternoon, indicating that aged aerosol and secondary organic aerosol (SOA) had a weaker BrC absorption capacity. There was a good overall correlation between BrC absorption and K⁺ concentrations. BrC absorption was also moderately related to the concentrations of ammonium cations (NH₄⁺) and nitrate anions (NO₃^-).