Atmospheric Brown Carbon (BrC) is a broad class of organic aerosols that absorb light and therefore influence radiative forcing of climate. They emerge from anthropogenic and natural sources, and they undergo significant transformations in chemical and optical properties in the processes of their atmospheric aging. Atmospheric concentrations of BrC from biomass burning (BB) emissions increase significantly as the planet becomes drier and warmer. Field campaigns measuring BB-BrC physicochemical properties have demonstrated that various ageing mechanisms can enhance or reduce BB-BrC light absorption. This presentation will focus on the investigation of a darkening-by-volatilization effect, shifting BB-BrC from very weakly to moderately absorbing. We identify chemical types of chromophores responsible for the darkening-by-volatilization transformations.  For comprehensive molecular analysis of BB-BrC mixtures, we employ high performance liquid chromatography, optical spectroscopy, and high-resolution mass spectrometry. Our results indicate that evaporation of small monoaromatic species and a buildup of multi-ring lignin fragments and substituted polyaromatics play a significant role in enhancing BB-BrC absorbance.  For quantitative assessment of our results and practical use in atmospheric models, we distinguish 3 broad chemically distinct fractions of BB-BrC and report their volatility, viscosity, and light absorption characteristics.

Evaporation of volatile components transforms composition and optical properties of brown carbon aerosol

Where thousands of chemistry professionals meet to share ideas and advance scientific and technical knowledge. Spring 2023 abstracts, posters, and presentations will launch at the end of March.

ACS Spring 2023

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.