Wildfire-smoke observations fill gap in estimating soot's role in climate change
Black carbon, or soot, from wildfires, transportation and other sources has a big impact on global warming, but a data gap has prevented climate-change models from accurately representing that influence. New work by Los Alamos National Laboratory closes the gap with a simple parameter for climate models. Credit: Los Alamos National Laboratory

Improving the amount of sunlight absorbed by black carbon in smoke from wildfires will help clear up a weak spot in the earth system models.

"Black carbon or soot is the next most potent climate warming agent after CO 2 and methane, despite a short lifetime of weeks, but its impact in climate models is still highly uncertain," said James Lee, a climate researcher at Los Alamos National Laboratory. The research will clear up the uncertainty.

There has been a long-time discrepancy between the amount of light absorbed by black carbon in smoke and the amount predicted by models due to how black carbon is mixed with other materials.

The team used the Center for Aerosol-gas forensic Experiments at Los Alamos to sample smoke from several wildfires over two summers in the Western United States, including the nearby Medio Fire in New Mexico in 2020.

The Department of Energy's Energy Exascale Earth System Model, or E3 SM, is being incorporated by the team at the Pacific Northwest National Laboratory. The evaluation of wildfire climate forcing and feedbacks will be improved by this.

Black carbon is a potent absorber of solar radiation and converts incoming light to atmospheric heating.

The composition of the smoke mixture can affect the net effect of the fire on the atmosphere. Smoke from large megafires spread around the world. There is a correlation between the increase in light absorption efficiency of soot with age and the growth in organic coating.

The soot that is currently approximated in models is captured by the discovery.

In order to provide robust estimates of warming by wildfire soot, we are pushing to incorporate it in climate models.

The climate impact of black carbon is not well known because of how it co-exists with other particles in the atmosphere.

A lack of understanding of how black carbon light-reflecting and -Absorbing properties evolve as it ages and undergoes complicated chemistry in the rapidly changing atmospheric conditions as wildfire smoke dispersals is part of the uncertainty. For a long time in the upper atmosphere, the cloud can linger.

Black carbon particles are formed by organic aerosols. The amount of light absorbed by the black carbon depends on the size of the aerosol and how it coats the soot.

The mixing state of smoke is idealized by climate models. The models underestimate the amount of radiation absorbed by black carbon because they don't account for the variation in organic coating. Large uncertainties and biases are caused by that.

The cost of single-particle modeling makes it impractical to use in earth- system models. Los Alamos researchers wanted to create parameters for black carbon that could be incorporated into earth- system models without having to spend a lot of money on modeling a lot of particles.

Sixty million smoke particles were analyzed by the Los Alamos team. They were able to account for variations in the amount of organic coating on each particle. The team used existing models to figure out how much light energy each particle absorbed and how much black carbon was absorbed. Their results matched independent measurements of smoke properties made in parallel, while modeling based on idealized black carbon particles didn't match observations The Los Alamos results can be scaled up to show the atmosphere.

The team was able to predict the amplification of black carbon from the ratio of the coating material to the volume of black carbon. The ratio can be used to determine the climate impact of black carbon.

More information: James E. Lee et al, Wildfire Smoke Demonstrates Significant and Predictable Black Carbon Light Absorption Enhancements, Geophysical Research Letters (2022). DOI: 10.1029/2022GL099334 Journal information: Geophysical Research Letters