Unraveling the Link between Real-Time Light-Absorption Properties and Offline Molecular Composition of Brown Carbon Aerosol
VAIOS MOSCHOS, Cade Christensen, Marc Fiddler, Barbara Turpin, Solomon Bililign, Jason Surratt,
NCAT & UNC-Chapel Hill Abstract Number: 314
Working Group: Aerosol Chemistry
AbstractThe radiative forcing of aerosols remains uncertain owing to their diverse sources, variable physicochemical properties, and inhomogeneous spatial distribution. Biomass burning (BB) significantly contributes to aerosol emissions, including the chemically complex light-absorbing organic (brown) carbon (BrC).
We conducted a series of smog chamber combustion experiments using biomass fuels from sub-Saharan Africa, a global hotspot source region of carbonaceous aerosols. To simulate atmospheric conditions, we examined the effects of relative humidity and photo-aging on primary emissions. We analyzed filter samples with ultra-performance liquid chromatography coupled in-line to a diode array detector and a high-resolution quadrupole time-of-flight mass spectrometer, with the latter equipped with an electrospray ionization source operated in both positive and negative ion modes.
We identified 182 individual BrC species (including isomers) with diverse polarities, grouped into distinct chemical classes: guaiacol and syringol derivatives, nitro-aromatic compounds, coumarins, stilbenes, and flavonoids. Employing an extensive set of authentic standards with distinct chromatographic responses, absorbance spectra, and fragmentation patterns, we quantified the chromophoric species and attempted mass closure. Notably, the standards represented two-thirds of the BrC mass identified using this analytical platform. We applied multivariate data analysis to interpret the complex molecular composition matrix.
We linked the molecular composition to real-time aerosol light-absorption properties (e.g., mass absorption cross-section, absorption Ångström exponent) based on calibrated aethalometer measurements. Furthermore, we assessed the atmospheric relevance of the chamber-generated BrC by analyzing night-/day-time aerosol filter samples from two locations in Botswana, Africa, at the onset of the 2022 fire/heating season (June-July).
Our study offers molecular-level insights into the emission/transformation of BB-derived BrC aerosol constituents associated with one of the world’s major yet neglected source regions, towards elucidating their environmental and climate-relevant effects.
VM acknowledges support from the Swiss-NSF (Postdoc.Mobility P500PN_210745). Field collection and chemical analysis are funded by the NSF (OISE-1559308, AGS-2100708).