Aethalometer-based Estimate of Mass Absorption Cross Section of Black Carbon Particles at an Urban Site of Gwangju

In this study, real-time absorption coefficients of carbonaceous species in PM2.5 was observed using a dual-spot 7-wavelength Aethalometer between November 1, 2016 and December 31, 2017 at an urban site of Gwangju. In addition, 24-hr integrated PM2.5 samples were simultaneously collected at the same site and analyzed for organic carbon and elemental carbon (OC and EC) using the thermal-optical transmittance protocol. A main objective of this study was to estimate mass absorption cross section (MAC) values of black carbon (BC) particles at the study site using the linear regression between aethalometer-based absorption coefficient and filter-based EC concentration. BC particles observed at 880 nm is mainly emitted from combustion of fossil fuels, and their concentration is typically reported as equivalent BC concentration (eBC). eBC concentration calculated using MAC value of 7.77 m(2)/g at wavelength of 880 nm, which was proposed by a manufacturer, ranged from 0.3 to 7.4 mu g/m(3) with an average value of 1.9 +/- 1.2 mu g/m(3), accounting for 7.3% (1.5 similar to 20.9%) of PM2.5. The relationship between aerosol absorption coefficients at 880 nm and EC concentrations provided BC MAC value of 15.2 m(2)/g, ranging from 11.4 to 16.2 m(2)/g. The eBC concentrations calculated using the estimated MAC of 15.2 m(2)/g were significantly lower than those reported originally from aethalometer, and ranged from 0.2 to 3.8 mu g/m(3), with an average of 1.0 +/- 0.6 mu g/m(3), accounting for 3.7% of PM2.5 (0.8 similar to 10.7%). Result from this study suggests that if the MAC value recommended by the manufacturer is applied to calculate the equivalent BC concentration and radiative forcing due to BC absorption, they would result in significant errors, implying investigation of an unique MAC value of BC particles at a study site.