Solid Particles or “Tar balls” from Wildfires Exhibit Enhanced Light Absorption

The Science

Burning of the Earth’s biomass is a major source of black carbon and organic carbon particles in the atmosphere, exerting a substantial influence on Earth’s radiation budget (i.e., the balance between incoming and outgoing radiation). Among these, solid-state, strongly absorptive brown carbon particles (solid S-BrC, commonly referred to as “tar balls”) can be particularly abundant in wildfire plumes. These particles significantly absorb solar radiation. However, their light absorption properties are often neglected or underestimated in global atmospheric models. This study provides a direct observation of water uptake by solid S-BrC emitted from recent wildfires in the Pacific Northwest. The findings reveal that water uptake by these “tar balls” enhance light absorption, leading to notable and previously uncharacterized impacts. These results highlight the need to explicitly incorporate the unique properties of solid S-BrC into atmospheric modeling to better understand and predict their role in the Earth’s radiation budget. 

Solid brown carbon particles emitted from wildfire with different water uptake potential (Image courtesy of Swarup China | Environmental Molecular Sciences Laboratory).

The Impact

Results from this study enhance understanding of the life cycle of brown carbon particles emitted from wildfire. This study improves the ability of researchers to model these abundant particles and their interactions with other atmospheric particles and chemicals, clouds, and the hydrogeological cycle, which is critical for more accurate prediction of global atmospheric conditions.

Summary

This study, led by a multi-institutional team of researchers, presents the chemical composition and light absorption properties of biomass-burning single particles emitted into the atmosphere during recent wildfires in the Pacific Northwest. The team used a combination of advanced analytical techniques, including spectro-microscopy, single-particle mass spectrometry, high-resolution mass spectrometry, and regional modeling to provide a comprehensive evaluation of the chemical and optical characteristics of biomass burning particles and their atmospheric impacts. Results reveal a significant presence of solid-state, highly absorptive brown carbon particles that influence Earth’s radiation budget. Notably, approximately half of these particles can uptake water to form a coating under high relative humidity environments. The coating can serve as a lens to refract light toward the absorptive brown carbon portions of particles, amplifying sunlight absorption. These findings clarify debated conceptual models regarding chemical reactions of solid S-BrC in the atmosphere, offering unique and valuable insights into the atmospheric effects of biomass-burning particles.

Contacts 

Zezhen Cheng | EMSL | zezhen.cheng@pnnl.gov

Swarup China | EMSL | swarup.china@pnnl.gov

Funding

A portion of the research was performed through a Large-Scale Research project from the Environmental Molecular Sciences Laboratory, a Department of Energy (DOE) Office of Science user facility. Additional support was provided by Manish Shrivastava’s DOE Early Career award, the Atmospheric System Research program sponsored by DOE’s Biological and Environmental Research program, and the Advanced Light Source, another DOE Office of Science user facility.

Publication

Z. Cheng, et al. “Enhanced light absorption for solid-state brown carbon from wildfires due to organic and water coatings.” Nature Communications 15, 10326 (2024). [DOI: 10.1038/s41467-024-54506-5]