Constraining the size distribution of mineral dust aerosols using theory, a compilation of literature measurements, and mesoscale modeling

Mineral dust aerosols impact Earth’s radiation budget through interactions with radiation, clouds, and ecosystems, which constitutes a substantial uncertainty in understanding past and predicting future climate changes. One of the causes of this large uncertainty is the poor understanding of the size distribution of emitted dust aerosols. In fact, recent work has indicated that mesoscale and global circulation models overestimate the fraction of emitted clay aerosols (< 2 μm diameter) by up to an order of magnitude relative to measurements (Kok, 2010, in review). We use simulations over North Africa with a mesoscale model (WRF-Chem) to test the performance of empirical size distributions used in the literature, as well as a theoretical size distribution derived from the analogy between the fragmentation of soil dust aggregates and the fragmentation of brittle materials such as glass. We compare the simulations to a suite of satellite, ground-based, and airplane measurements during the African Monsoon Multidisciplinary Analysis campaign in early 2006. Using a statistical analysis of model discrepancies with measurements, we determine the emitted size distribution that maximizes the agreement between model and measurements. Since North Africa constitutes the world’s largest source of dust, our results can be used to guide the parameterization of the emitted dust size distribution in mesoscale and global circulation models.