Geoscience Reference
In-Depth Information
The most important nutrient that is transported with mineral dust is iron (see
Chap. 14 , Jickells et al. 2005 ; Mahowald et al. 2005 ). The major carriers of Fe in
mineral dust are iron oxide (e.g., hematite), iron hydroxide (e.g., goethite), and/or
Fe-bearing sheet silicates (mainly members of the smectite and chlorite group).
Journet et al. ( 2008 ) emphasized that the soluble iron (Fe 2C ) in mineral dust is
mainly derived from the different clay minerals and not from the iron oxides and
hydroxides. Hence, the primary fraction of clay minerals in a dust sample (and
its evolution during transport) is crucial for the supply of bioavailable iron to
the different ecological compartments. However, as mentioned above, this fraction
largely varies from a few wt% to more than 60 wt% (Lawrence and Neff 2009 ;
Scheuvens et al. 2013 ) and is only partly determined by the soil type of the
source region. The clay mineral fraction probably also strongly depends on the
wind speed during emission (with higher wind speed favoring lower abundance of
clay minerals). During transport of mineral dust, its mass concentration generally
decreases due to deposition and dispersion, whereas the fraction of clay minerals
increases relatively, owing to preferential settling of larger particles (mainly quartz,
carbonates, and feldspar) during the early stages of transport. As result, an increase
in dust “fertility” is expected.
The relationship between human health and environmental mineral dust exposure
is not well defined (see also Chap. 15 ) , and studies are often restricted to a
comparison of elevated mass concentrations during dust events (e.g., PM 10 )and
their effects on health or mortality (e.g., Chen et al. 2004 ;Yangetal. 2005 ;Prospero
et al. 2008 ; Dadvand et al. 2011 ; Tobías et al. 2011 ; Thalib and Al-Taiar 2012 ). In
southern Europe, the input of Saharan dust is also responsible for exceedances of
PM 10 (and PM 2.5 ) limit values set by the directive for air quality in Europe (Querol
et al. 2009 ; Remoundaki et al. 2012 ). For future studies, it would be highly desirable
to include more often compositional parameters (especially obtained by individual-
particle analysis) and particle size distributions to gain a deeper understanding of
the health effects of mineral dust intrusions, despite the fact that anthropogenic
emissions (e.g., traffic related) are clearly more toxic than dust particles (e.g.,
Samoli et al. 2011 ).
In Table 2.2 , we list the major topics that are associated with the uplift, transport,
and settlement of mineral dust and assign a preferred physicochemical analytical
method for each field of investigation. It becomes obvious that determination of the
dust mineralogy by XRD and (automated) chemical and morphological analysis of
dust particles are powerful tools for a better understanding of origin and impacts of
mineral dust. It is suggested that a combination of both techniques (e.g., automated
particle analysis in a transmission electron microscope) could be very helpful in
impact studies of mineral dust and will be hopefully available in the future.
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