Mineral dust emission from the Bodélé Depression, northern Chad, during BoDEx 2005

Abstract

[1] Mineral dust in the atmosphere is an important component of the climate system but is poorly quantified. The Bodélé Depression of northern Chad stands out as the world's greatest source region of mineral dust into the atmosphere. Frequent dust plumes are a distinguishing feature of the region's climate. There is a need for more detailed information on processes of dust emission/transport and dust optical properties to inform model simulations of this source. During the Bodélé Dust Experiment (BoDEx) in 2005, instrumentation was deployed to measure dust properties and boundary layer meteorology. Observations indicate that dust emission events are triggered when near-surface wind speeds exceed 10 ms À1 , associated with synoptic-scale variability in the large-scale atmospheric circulation. Dust emission pulses in phase with the diurnal cycle of near-surface winds. Analysis of dust samples shows that the dust consists predominantly of fragments of diatomite sediment. The particle size distribution of this diatomite dust estimated from sun photometer data, using a modified Aeronet retrieval algorithm, indicates a dominant coarse mode (radius centered on 1-2 mm) similar to other Saharan dust observations. Single-scattering albedo values are high, broadly in line with other Saharan dust even though the diatomite composition of dust from the Bodélé is likely to be unusual. The radiative impact of high dust loadings results in a reduction in surface daytime maximum temperature of around 7°C in the Bodélé region. Using optical and physical properties of dust obtained in the field, we estimate the total dust flux emitted from the Bodélé to be 1.18 ± 0.45 Tg per day during a substantial dust event. We speculate that the Bodélé Depression ($10,800 km 2 ) may be responsible for between 6-18% of global dust emissions, although the uncertainty in both the Bodélé and global estimates remains high.

Size distribution, shape, and composition of mineral dust aerosols collected during the African Monsoon Multidisciplinary Analysis Special Observation Period 0: Dust and Biomass‐Burning Experiment field campaign in Niger, January 2006

“…These are microorganisms which are generally found in dry lake bed such as of the Bodélé depression [Todd et al, 2007]. Diatoms were observed generally as fragments, suggesting that they already spent a considerable time in the atmosphere at the time of collection.…”

The Spatial Variation of Dust Particulate Matter Concentrations during Two Icelandic Dust Storms in 2015

“…Generation of such fine particles is associated with mechanical processes of glaciers and fluvial processes [27]. However, even the finest lacustrine sediments produced from the most active dust hot spots of the world, such as the Bodele Depression in the Sahara or the Sistan Basin in Iran do not consist of such high amounts of submicron particles as observed in Icelandic dust [3,10,13,43,44].…”

Estimating the global abundance of ground level presence of particulate matter (PM2.5)

“…Africa -The Bodelle depression (L) is Chad's lowest point on the Sahara's southern edge that supplies the Amazon forest with the majority of its mineral dust Koren et al, 2006;Washington et al, 2006a,b;Todd et al, 2007;Bouet et al, 2012). The high abundance of PM 2.5 over the Bodelle is clearly visible.…”