Scientists Uncover the Role of Tar Particles from Wildfire Smoke in Earth’s Atmosphere

Days after a wildfire, a type of smoke can linger in the atmosphere that contains tiny, brown, light-absorbing particles known as tar balls. These particles are believed to have a significant impact on Earth’s radiative balance, and as a result, a role in both the warming and cooling of the atmosphere.

The formation of these tar balls is not yet well-known, which makes studying their impact on the environment quite difficult. Claudio Mazzoleni, a physics professor at Michigan Technological University, stated that more information is needed on how and why these particles influence the atmosphere. To address this knowledge gap, Mazzoleni and a team of researchers conducted a study overseen by the Environmental Molecular Sciences Laboratory (EMSL).

The team used advanced spectroscopy tools to analyze individual tar balls dispersed over a mountainous region in northern Italy, mimicking the compositions and atmospheric conditions of these particles. This required expertise and instrumentation available at EMSL. The researchers determined the optical properties, refractive index, and radiative forcing of the tar balls, which helped understand their potential for cooling or warming the region.

Tar balls are challenging to study due to their presence among thousands of other particles in the atmosphere. Additionally, not all smoke contains tar balls. Therefore, analyzing individual particles and their specific properties becomes crucial. The team collected aerosol samples from Mt. Cimone in Italy, characterized their chemical composition and carbon functionalities, and estimated radiative forcing using the Santa Barbara DISORT model.

The findings revealed that a layer of tar balls above vegetation would exert a mild positive radiative forcing under clear sky conditions, suggesting a warming effect on the atmosphere. Furthermore, it was observed that the warming effect increased when clouds were present below the aerosol layer. Despite these significant findings, the researchers emphasized that tar balls are still a complex puzzle requiring further analysis under various conditions, locations, and parameters.

Looking ahead, Mazzoleni expressed the importance of collecting samples from different fire-affected areas and expanding the dataset to enhance modeling and understanding. The more data researchers acquire, the better equipped they will be to comprehend the impact of tar balls and improve predictions and mitigation strategies related to atmospheric particles from biomass burning events.