Quantifying Mineral Dust Mass Budgets: Terminology, Constraints, and Current Estimates

Mineral dust aerosol is created by wind erosion of soil particles. In addition to its direct radiative effect, dust aerosol mediates ocean carbon uptake and the chemical cycles of other aerosols like sulfates. Dust observations during the past decade span measurements of local concentration and deposition to global satellite retrievals of aerosol optical thickness [Prospero et al., 2002]. Measurements of dust emission, whereby soil particles enter the atmosphere, are scarce. Because no single data set is sufficient to constrain the three-dimensional distribution of dust aerosol and its evolution with time, the dust cycle is currently estimated using models that are constrained by available measurements and retrievals. However, a survey of recent models (Table 1) shows that estimates of emission range over more than a factor of two. This translates into a corresponding uncertainty in the climate effect of dust. One goal of this article is to draw awareness to the wide range of model estimates of dust emission and atmospheric loading. Comparison is made difficult by the different assumptions made by modelers. For example, some models include dust sources created by human disturbance of the soil (by agriculture or overgrazing, for example), while others include only natural sources. Participants at the Second International Workshop on Mineral Dust convened in Paris September 10–12, 2003, agreed that the binary division of dust into “natural” and “anthropogenic” emissions is inadequate, and that scientific progress, and the policy which it informs, requires more precise nomenclature. While natural