In this post, Alexander Laskin, professor of chemistry in the College of Science and a member of the Purdue Institute for a Sustainable Future, discusses his recently published research “Enhanced Light Absorption and Elevated Viscosity of Atmospheric Brown Carbon through Evaporation of Volatile Components,” which appears in Environmental Science & Technology, with the support of the international collaboration grant from the National Science Foundation and the USA-Israel Binational Science Foundation.
What did you want to know?
The increase of atmospheric aerosols from wildfires significantly affects various climate and atmospheric processes, including radiative forcing, long-range transport of pollutants, aerosol-cloud interactions, and alterations to snow and ice surfaces. The extent to which aerosols from wildfires influence these processes remains uncertain, posing challenges for atmospheric models to accurately project their global impact both currently and in the future.
Of particular importance is establishing a predictive understanding of the relationship between aerosol molecular composition and its light absorption properties. Biomass burning aerosols from wildfires exhibit a wide range of compositions and optical properties due to its diverse sources and dynamic transformations in the atmosphere. This variability necessitates comprehensive studies investigating the original aerosol emissions and the effects of atmospheric aging on the composition and optical properties of biomass burning aerosols. Our reported study examined gas-particle partitioning dynamics of aerosol components and their influence on accurately characterizing the optical properties of aerosols emitted from biomass burning.
What did you achieve?
Optical measurements and chemical characterization in our study revealed that the evaporative loss of smaller, less absorbing compounds leads to the accumulation of larger, more strongly absorbing constituents, significantly darkening the overall aerosol mixtures. Concurrently, the volatility and viscosity of the aerosols evolve, favoring the preservation of less volatile and more viscous components, which in turn additionally augment the optical properties of aerosols. The darkening trend observed in our experiments aligns with findings from numerous field studies, reinforcing the validity of our results.
What is the impact of this research?
Our study has significant implications for various atmospheric processes. Aerosols from wildfires that undergo darkening and become more viscous play a crucial role in atmospheric phenomena, including radiative forcing, hygroscopicity, cloud formation propensity, atmospheric composition, and air quality. For example, viscous, solid-like particles are effective carriers of absorbed harmful compounds, shielding them from oxidants and degradation processes. Additionally, solid (highly viscous) particles influence nucleation mechanisms in mixed-phase cloud formation, favoring heterogeneous ice nucleation over homogeneous ice nucleation, which affects cloud formation and precipitation.
Atmospherically aged, rigid, and viscous aerosols undergo slower photochemical transformations and ozonolysis, contributing to their chemical inertness as they disperse away from wildfire emission sources. This inertness can amplify their contribution to radiative forcing processes, making them a critical factor in understanding and modeling Earth’s climate system.