Enhanced Light Absorption and Radiative Forcing by Black Carbon Agglomerates.

Area of Science:

• Atmospheric Science
• Climate Modeling
• Radiative Transfer

Background:

• Black carbon (BC) is recognized by the Intergovernmental Panel on Climate Change as a key driver of global warming due to its radiative forcing (RF) impact.
• Current climate models may significantly underpredict BC's direct RF because they often assume a simplified spherical morphology for BC particles.

Purpose of the Study:

• To investigate the impact of realistic black carbon morphology on its radiative forcing.
• To quantify the enhancement in light absorption and RF due to light scattering in BC agglomerates.

Main Methods:

• Applied Rayleigh-Debye-Gans theory and discrete dipole approximation to model light scattering in BC agglomerates.
• Incorporated recent relations for refractive index and lensing effects.
• Utilized ECHAM-HAM simulations with realistic BC morphology and coatings.

Main Results:

• Light absorption of BC is enhanced by approximately 20% due to multiple light scattering between primary particles, irrespective of agglomerate compactness.
• Simulations reveal high direct RF (3-5 W/m²) in regions like East/South Asia and Africa.
• These findings align with satellite and AERONET observations.

Conclusions:

• Realistic BC morphology significantly increases its radiative forcing, challenging previous model assumptions.
• BC emissions contribute substantially to regional climate warming, estimated at 0.75-1.25 °C.
• Accurate representation of BC's physical properties is crucial for precise climate change projections.