Light-absorbing organic aerosol commonly termed as Brown carbon (BrC) is a significant contributor to radiative forcing of the Earth’s climate and also is of toxicological concern. Understanding the environmental effects of BrC, its sources, formation, and aging processes requires fundamental knowledge of its chromophores and characterization of their light-absorption properties. This seminar will highlight our recent analytical chemistry developments and applications in the area of molecular-level characterization of BrC that provided first insights into diverse composition and properties of its common chromophores. We present the chemical analysis of chromophores reported in a number of case studies of BrC materials associated with emissions from biomass burning and anthropogenic secondary organic aerosols. The results show that BrC chromophores include organic molecules with various structures, polarities, and volatilities. Understanding their chemical identity requires multi-modal analysis employing complementary separation and ionization approaches in combination with high resolution mass spectrometry. These studies allow assessment of BrC optical properties and relating them to fractional contributions from different classes of chromophores such as aromatic carboxylic acids, nitro-phenols; substituted, heterocyclic and pure polycyclic aromatic hydrocarbons.
