Improved Parameterization for the Size Distribution of Emitted Dust Aerosols Reduces Model Underestimation of Super Coarse Dust

Aircraft measurement campaigns have revealed that super coarse dust (diameter >10 mu m) surprisingly accounts for approximately a quarter of aerosols by mass in the atmosphere. However, most global aerosol models either underestimate or do not include super coarse dust abundance. To address this problem, we use brittle fragmentation theory to develop a parameterization for the emitted dust size distribution that includes emission of super coarse dust. We implement this parameterization in the Community Earth System Model (CESM) and find that it brings the model in good agreement with aircraft measurements of super coarse dust close to dust source regions. However, the CESM still underestimates super coarse dust in dust outflow regions. Thus, we conclude that the model underestimation of super coarse atmospheric dust is in part due to the underestimation of super coarse dust emission and likely in part due to errors in deposition processes.

Automated summary

Aircraft measurement campaigns have shown that super coarse dust, which accounts for approximately a quarter of aerosols by mass in the atmosphere, is often underestimated or not included in global aerosol models. To address this issue, a parameterization for the emitted dust size distribution, including super coarse dust, was developed using brittle fragmentation theory. Implementing this parameterization in the Community Earth System Model (CESM) improved the agreement with aircraft measurements in dust source regions, but underestimated super coarse dust in dust outflow regions. This suggests that the underestimation of super coarse atmospheric dust in the model is partly due to the underestimation of dust emission and potentially errors in deposition processes.