Particle size amplification of black carbon by scattering measurement due to morphology diversity

Black carbon (BC) is an important aerosol species due to its strong heating of the atmosphere accompanied by cooling of the Earth's surface, but its radiative forcing is poorly constrained by different regional size distributions due to uncertain reproductions of a morphologically simplified model. Here, we quantify the BC morphological effect on measuring the particle size using an aggregate model. We show that the size distributions of loose BC particles could account for up to 45% underestimation by morphological simplification, leading to up to 25% differences, by relying on a simplified model to estimate radiative forcing. We find that the BC particle size is remarkably amplified for looser and larger BC aggregates by angular scattering observations. We suggest that the BC morphological diversity can be neglected in forward scattering angles (<30 degrees), which is a useful supplement to reduce the uncertainty of radiative forcing assessment.

Automated summary

Black carbon (BC) is an important aerosol species with significant radiative forcing effects, but the uncertainty in reproducing its morphologically simplified model leads to poorly constrained estimates. By using an aggregate model, we demonstrate that loose BC particles can be underestimated by up to 45% due to morphological simplification, leading to differences of up to 25% in estimated radiative forcing. We also observe that looser and larger BC aggregates exhibit amplified particle sizes through angular scattering. Our findings suggest that the morphological diversity of BC can be neglected at forward scattering angles (<30 degrees), which helps reduce the uncertainty in radiative forcing assessment.