Dust Production Mechanisms - Mineral Dust: A Key Player in the Earth System - page 93

or non-active dust sources. However, additional investigation on the saltation and
sandblasting processes, both from a theoretical and experimental point of view, is
still needed. Special attention must be paid to the link with soil properties and its
implications on the size distribution of the emitted dust.

Keywords Erosion threshold ￿ Dust production ￿ Soil moisture ￿ Surface rough-
ness ￿ Particle size ￿ Dust emission ￿ Surface ￿ Saltation ￿ Numerical models ￿
Field observations

5.1 Introduction

Aeolian erosion in arid and semi-arid regions is the main source of atmospheric
dust particles. Mineral dust represents about 40 % of the global annual emissions
of tropospheric aerosols (IPCC 2007 ). Mineral dust can be transported thousands of
kilometres away from its sources. In the atmosphere, mineral dust has a significant
impact on the Earth radiative budget by scattering radiation in the visible range
and absorbing it in the infrared (IR) (see Chaps. 11 and 13 ) . This radiative impact
induces interactions with local and regional dynamics that can affect, for example,
the quality of meteorological forecasts over West Africa (Tompkins et al. 2005 ).
Mineral dust is now included in forecasting models (e.g. Milton et al. 2008 )to
improve climate projections and the simulations of dust storms and visibility (see
Chap. 10 ) . On a longer timescale, the soil loss due to dust export from arid and
semi-arid regions contributes to desertification processes (Rajot 2001 ). On the
opposite, dust deposition can be a significant source of nutrients or micronutrients
(phosphorus, iron, etc.) for remote oceanic or continental ecosystems (e.g. Jickells
et al. 2005 ; Mahowald et al. 2008 ; see Chap. 14 ) . Inside and close to source
regions, dust storms are responsible for severe reductions of the horizontal visibility,
which induce social and economical impacts by affecting, for example, aerial and
terrestrial traffic (e.g. Pauley et al. 1996 ). Finally, mineral dust can have sanitary
impacts in source and transport regions (see Chap. 15 ) . As an example, mineral
dust is suspected to play a role in meningitis epidemics in the Sahelian region (e.g.
Thomson et al. 2006 ; Agier et al. 2013 ; Martiny and Chiapello 2013 ).
Uncertainties in the evaluation of mineral dust impacts are in large part due to its
spatial and temporal distribution. Surface concentrations vary over several orders of
magnitude (0.001-1,000 gm 3 ) as a function of the distance to the dust sources
(Marticorena and Formenti 2013 ). This variability is largely due to dust emission.
Current estimates of mineral dust emissions are mainly derived from modelling
approaches. The simulated global dust emissions reported from the intercomparison
exercise of the AEROCOM project ( http://aerocom.met.no/ ) range between 500 and
3,000 Mt year 1 with a median value of 1,500 Mt year 1 and a standard deviation

of 1,000 Mt year 1 (Huneeus et al. 2011 ). The ratio between the median estimation
and the standard deviation is lower than 80 % for the main dust source regions of
the northern hemisphere (North Africa, Middle East, Asia) but much higher for the