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Enhanced radiative cooling by large aerosol particles from wildfire-driven thunderstorms
Yaowei Li1, John A Dykema1, David A Peterson2
1School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA.
Science Advances
|December 10, 2025
Summary
Wildfires create pyrocumulonimbus (pyroCb) clouds, sending smoke high into the atmosphere. These large smoke particles cause significant radiative cooling, an effect potentially underestimated by climate models.
Area of Science:
- Atmospheric Science
- Climate Science
- Aerosol Science
Background:
- Large wildfires generate pyrocumulonimbus (pyroCb) clouds, injecting smoke aerosols into the upper troposphere and lower stratosphere (UT/LS).
- The radiative effects of pyroCb smoke aerosols are poorly understood due to limited direct measurements.
- PyroCb smoke aerosols persist for months, influencing climate and atmospheric radiative balance.
Purpose of the Study:
- To present in situ aircraft measurements of aged pyroCb smoke aerosols.
- To address the observational gap in aerosol evolution from fresh to aged states.
- To quantify the radiative effects of large pyroCb smoke particles.
Main Methods:
- In situ aircraft measurements of 5-day-old pyroCb smoke aerosols.
- Analysis of aerosol particle size distribution and composition.
- Calculation of radiative effects based on measured aerosol properties.
Main Results:
- Sampled pyroCb smoke contained unusually large aerosol particles (500-600 nm in diameter).
- These large particles formed through cloud processing and coagulation in the UT/LS.
- Large particles increased outgoing radiation by 30-36%, enhancing atmospheric radiative cooling.
Conclusions:
- PyroCb smoke aerosols have distinct properties (larger particle sizes) compared to typical smoke.
- Current climate models may underestimate the cooling effect of pyroCb smoke due to assumed smaller particle sizes.
- Accurate representation of pyroCb aerosol properties is crucial for improving climate projections, especially with increasing wildfire frequency.
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