Contribution of the world's main dust source regions to the global cycle of desert dust

Even though desert dust is the most abundant aerosol by mass in Earth's atmosphere, the relative contributions of the world's major source regions to the global dust cycle remain poorly constrained. This problem hinders accounting for the potentially large impact of regional differences in dust properties on clouds, the Earth's energy balance, and terrestrial and marine biogeochemical cycles. Here, we constrain the contribution of each of the world's main dust source regions to the global dust cycle. We use an analytical framework that integrates an ensemble of global aerosol model simulations with observationally informed constraints on the dust size distribution, extinction efficiency, and regional dust aerosol optical depth (DAOD). We obtain a dataset that constrains the relative contribution of nine major source regions to size-resolved dust emission, atmospheric loading, DAOD, concentration, and deposition flux. We find that the 22-29 Tg (1 standard error range) global loading of dust with a geometric diameter up to 20 mu m is partitioned as follows: North African source regions contribute similar to 50% (11-15 Tg), Asian source regions contribute similar to 40% (8-13 Tg), and North American and Southern Hemisphere regions contribute similar to 10% (1.8-3.2 Tg). These results suggest that current models on average overestimate the contribution of North African sources to atmospheric dust loading at similar to 65 %, while underestimating the contribution of Asian dust at similar to 30 %. Our results further show that each source region's dust loading peaks in local spring and summer, which is partially driven by increased dust lifetime in those seasons. We also quantify the dust deposition flux to the Amazon rainforest to be similar to 10 Tg yr(-1), which is a factor of 2-3 less than inferred from satellite data by previous work that likely overestimated dust deposition by underestimating the dust mass extinction efficiency. The data obtained in this paper can be used to obtain improved constraints on dust impacts on clouds, climate, biogeochemical cycles, and other parts of the Earth system.

Automated summary

This study constrained the relative contributions of major dust source regions to the global dust cycle, finding that North African and Asian regions are the main contributors, and dust loading peaks in local spring and summer. The data obtained in this paper can be used to improve constraints on dust impacts on clouds, climate, biogeochemical cycles, and other parts of the Earth system.