70
J. M. Pro spero
10000,------------------------------------------------------,
1000
Fine particle mode «2.5 ~m diameter)
I. Non-dust - Dust 1
100
1O-J
I·I
•• t •••• : ••• :!tt.!.:.!.!.1.!
!I .. rI
0.1 ~[',-,-,-,r-r-r-r-r-r-r-r-r-.-.-,-,-,-,-,-,--r-r-r-r-.-.-.-.-.-.-.-,-,-,r-r-~
Th b
~ ~ ~
~
~ ~
K ~ 0
V ~ G ~ ~ G fu
Fig. 2.12. Element enrichment factors calculated for the fine fraction «2.5 f.lm diameter) of aerosol
samples collected from Mediterranean air masses. Element concentrations are normalized to Al and
compared to average crustal abundances. Data are plotted separately for African dust events and nondust events. The larger enrichment factors obtained from non-dust events reflects the impact of pollutants from Europe, but even the dust events show the effects of the add-mixing of pollutant aerosols. (redrawn from Gullu et al. 1996, Fig. 5). The square symbols are data from samples dominated by dust. The
diamond symbols are data from samples that contain substantial pollution aerosol from European sources
2.5.4
Mineralogical Composition
The mineralogy of dust has been widely studied. For reviews that touch on this subject, see Pro spero 1981; Leinen and Sarnthein 1989; Guerzoni and Chester 1996; Pye 1987,
1989. Dusts typically contain minerals such as quartz, kaolinite, chlorite, illite, smectite,
calcite, etc. The mineralogy of dust from specific source regions shows a consistency
similar to that noted for elemental composition - for example, African dust carried to
Barbados during the summer months (Glaccum and Pro spero 1980). But various studies have shown regional differences in dust composition. Dusts originating from lowlatitude dust sources (e.g. south of the Sahara in North Africa) tend to have more kaolinite than dusts from mid-latitude sources; conversely, mid-latitude sources tend to
have more illite (Glaccum and Prospero 1980; Prospero 1981). The relative concentrations of these two minerals reflect climate differences that result in differences in mineral weathering processes. Indeed, differences in mineral composition can be used to
broadly identify source regions, for example in North Africa (Herrmann et al. 1996;
Molinaroli 1996). Similarly, large differences are noted for dusts transported over the
North Pacific from sources in Asia and North America (Blank et al. 1985; Merrill et al.
1994; Leinen et al. 1994). The differences in mineralogy could conceivably be used to
trace dust sources on a global scale, but this is difficult because the properties of potential soil sources are poorly characterized (Claquin et al. 1999).
2.5.5
Deposition of Dust to the Oceans
Estimates of the global dust budget vary widely, ranging from 1000 to 5000 Mt yr- 1
(Duce 1995; Prospero 1996a). Because of the complexity of the generation and transport processes, it has been difficult to develop global dust models. A number of mod-
J. M. Pro spero
10000,------------------------------------------------------,
1000
Fine particle mode «2.5 ~m diameter)
I. Non-dust - Dust 1
100
1O-J
I·I
•• t •••• : ••• :!tt.!.:.!.!.1.!
!I .. rI
0.1 ~[',-,-,-,r-r-r-r-r-r-r-r-r-.-.-,-,-,-,-,-,--r-r-r-r-.-.-.-.-.-.-.-,-,-,r-r-~
Th b
~ ~ ~
~
~ ~
K ~ 0
V ~ G ~ ~ G fu
Fig. 2.12. Element enrichment factors calculated for the fine fraction «2.5 f.lm diameter) of aerosol
samples collected from Mediterranean air masses. Element concentrations are normalized to Al and
compared to average crustal abundances. Data are plotted separately for African dust events and nondust events. The larger enrichment factors obtained from non-dust events reflects the impact of pollutants from Europe, but even the dust events show the effects of the add-mixing of pollutant aerosols. (redrawn from Gullu et al. 1996, Fig. 5). The square symbols are data from samples dominated by dust. The
diamond symbols are data from samples that contain substantial pollution aerosol from European sources
2.5.4
Mineralogical Composition
The mineralogy of dust has been widely studied. For reviews that touch on this subject, see Pro spero 1981; Leinen and Sarnthein 1989; Guerzoni and Chester 1996; Pye 1987,
1989. Dusts typically contain minerals such as quartz, kaolinite, chlorite, illite, smectite,
calcite, etc. The mineralogy of dust from specific source regions shows a consistency
similar to that noted for elemental composition - for example, African dust carried to
Barbados during the summer months (Glaccum and Pro spero 1980). But various studies have shown regional differences in dust composition. Dusts originating from lowlatitude dust sources (e.g. south of the Sahara in North Africa) tend to have more kaolinite than dusts from mid-latitude sources; conversely, mid-latitude sources tend to
have more illite (Glaccum and Prospero 1980; Prospero 1981). The relative concentrations of these two minerals reflect climate differences that result in differences in mineral weathering processes. Indeed, differences in mineral composition can be used to
broadly identify source regions, for example in North Africa (Herrmann et al. 1996;
Molinaroli 1996). Similarly, large differences are noted for dusts transported over the
North Pacific from sources in Asia and North America (Blank et al. 1985; Merrill et al.
1994; Leinen et al. 1994). The differences in mineralogy could conceivably be used to
trace dust sources on a global scale, but this is difficult because the properties of potential soil sources are poorly characterized (Claquin et al. 1999).
2.5.5
Deposition of Dust to the Oceans
Estimates of the global dust budget vary widely, ranging from 1000 to 5000 Mt yr- 1
(Duce 1995; Prospero 1996a). Because of the complexity of the generation and transport processes, it has been difficult to develop global dust models. A number of mod-