Is Black Carbon an Unimportant Ice-Nucleating Particle in Mixed-Phase Clouds?

Area of Science:

• Atmospheric Chemistry
• Cloud Physics
• Aerosol Science

Background:

• Black carbon (BC) is hypothesized to influence mixed-phase clouds as an ice-nucleating particle (INP).
• Existing literature presents highly variable data on BC's ice nucleation efficiency in supercooled water.
• Contradictory findings necessitate further experimental investigation into BC's role in cloud formation.

Purpose of the Study:

• To experimentally determine the ice-nucleating ability of black carbon (BC) particles in immersion mode.
• To compare the ice nucleation potential of BC with other known INPs like K-feldspar and marine organic aerosol.
• To model the atmospheric relevance of BC as an INP and define parameters for future studies.

Main Methods:

• Laboratory experiments measuring immersion mode ice nucleation for BC from n-decane and eugenol fuels.
• Utilizing a global aerosol model to quantify the relative importance of BC as an INP.
• Comparing experimental BC INP data with feldspar and marine organic aerosol.

Main Results:

• New experimental data show no significant heterogeneous ice nucleation by BC particles from the tested fuels.
• BC contributes orders of magnitude less as an INP compared to K-feldspar and marine organic aerosol, based on upper limits from laboratory data.
• Previous representations of BC's atmospheric ice-nucleating ability, based on older data, yield unrealistic results.

Conclusions:

• Black carbon is significantly less effective as an ice-nucleating particle than previously assumed, particularly compared to mineral dust and organic aerosols.
• While BC's complexity means it cannot be entirely dismissed, current evidence suggests a minimal role in atmospheric ice nucleation.
• Future research should focus on defining the specific active site densities required for BC to become atmospherically relevant, guiding experimental sensitivity.