Scavenging of black carbon by ice crystals over the Northern Pacific

Although the mass and number concentrations of BC were 7-25 times lower in crystal residuals than in particles outside of cloud, twice as many of the residuals (31%) contained BC compared to 17% of the particles in cloud-free air. In addition the average mass equivalent diameter (MED) of BC was 10% larger in crystal residuals than in particles outside of cloud.

These differences in crystal residuals compared to the background aerosols suggest that inertial scavenging is a significant mechanism for removing BC compared to removal by nucleation. The scavenging efficiency, calculated as the BC mass in condensed cloud water, ranged from 7-44 ng of carbon per gram of water, consistent with previous studies in marine stratus clouds.