Molecular Dynamics and Light Absorption Properties of Atmospheric Dissolved Organic Matter

The light-absorbing organic aerosol referred to as brown carbon (BrC) affects the global radiative balance. The linkages between its molecular composition and light absorption properties and how environmental factors influence BrC composition are not well understood. In this study, atmospheric dissolved organic matter (ADOM) in 55 aerosol samples from Guangzhou was characterized using Fourier transform ion cyclotron resonance mass spectrometry and light absorption measurements. The abundant components in ADOM were aliphatics and peptide-likes (in structure), or nitrogen- and sulfur-containing compounds (in elemental composition). The light absorption properties of ADOM were positively correlated with the levels of unsaturated and aromatic structures. Particularly, 17 nitrogen-containing species, which are identified by a random forest, characterized the variation of BrC absorption well. Aggregated boosted tree model and nonmetric multidimensional scaling analysis show that the BrC composition was largely driven by meteorological conditions and anthropogenic activities, among which biomass burning (BB) and OH radical were the two important factors. BrC compounds often accumulate with elevated BB emissions and related secondary processes, whereas the photolysis/photooxidation of BrC usually occurs under high solar radiance/(OH)-O-center dot concentration. This study first illuminated how environmental factors influence BrC at the molecular level and provided clues for the molecular-level research of BrC in the future.

Automated summary

This study used Fourier transform ion cyclotron resonance mass spectrometry and light absorption measurements to characterize atmospheric dissolved organic matter (ADOM) in aerosol samples from Guangzhou, revealing the influence of environmental factors on the molecular composition and light absorption properties of BrC. Nitrogen-containing species played a key role in the variation of BrC light absorption. Meteorological conditions and anthropogenic activities were identified as the main drivers of BrC composition.