Abstract. Light-absorbing organic carbon (or brown carbon, BrC) in atmospheric
particles has received much attention for its potential role in global
radiative forcing. While a number of field measurement campaigns have
differentiated light absorption by black carbon (BC) and BrC, the chemical
characteristics of BrC are not well understood. In this study, we present
co-located real-time light absorption and chemical composition measurements
of atmospheric particles to explore the relationship between the chemical and
optical characteristics of BrC at a suburban site downwind of Guangzhou,
China, from November to December 2014. BrC and BC contributions to light
absorption were estimated using measurements from a seven-wavelength
aethalometer, while the chemical composition of non-refractory PM1 was
measured with a high-resolution time-of-flight aerosol mass spectrometer
(HR-ToF-AMS). Using the absorption Ångström exponent (AAE) method, we
estimated that BrC contributed 23.6 % to the total aerosol absorption at
370 nm, 18.1 % at 470 nm, 10.7 % at 520 nm, 10.7 % at 590 nm,
and 10.5 % at 660 nm. Biomass burning organic aerosol (BBOA) has the
highest mass absorption coefficient among sources of organic aerosols. Its
contribution to total brown carbon absorption coefficient decreased but that
of low-volatility oxygenated organic aerosol (LVOOA) increased with
increasing wavelength, suggesting the need for wavelength-dependent light
absorption analysis for BrC in association with its chemical makeup. Clear
correlations of N-containing ion fragments with absorption coefficient were
observed. These correlations also depended on their degrees of
unsaturation/cyclization and oxygenation. While the current study relates
light absorption by BrC to ion fragments, more detailed chemical
characterization is warranted to constrain this relationship.
Chemical characteristics of brown carbon in atmospheric particles at a suburban site near Guangzhou, China
