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1
10
100
Sahara ground-based
Morocco
1
Niger
2
Niger
3
Morocco
4
Niger
5
Niger
6
Mauritania/Mali
7
Western Africa
8
Benin
9
Dakar coast
10
Cape Verde
11
Cape Verde
12
Cape Verde
13
Canary Islands
14
Canary Islands
15
Portugal
16
Portugal
17
Puerto Rico
15
UAE
18
Iraq
18
Yemen/Oman
18
Arabian Peninsula
16
Namibia
19
China
20
China
21
Sea of Japan
22
Sea of Japan
23
Japan
24
Taiwan
25
Arizona
26
Australia
27
Sahara airborne
Sahara transport
Arabian Peninsula
Southern Africa
Asia
Northern America
Australia
1
10
100
particle mode diameter, µm
Fig. 2.2
Number modal diameters detected by atmospheric measurements for different dust
situations.
1
Kandler et al. (
2009
),
2
Rajotetal.(
2008
),
3
Sow et al. (
2009
),
4
Weinzierl et al.
(
2009
),
5
Osborne et al. (
2008
),
6
Chou et al. (
2008
),
7
Ryder et al. (
2013
),
8
Johnson and Osborne
(
2011
),
9
Crumeyrolle et al. (
2011
),
10
McConnell et al. (
2008
),
11
Haywood et al. (
2003a
),
12
Schladitz et al. (
2011
),
13
Weinzierl et al. (
2011
),
14
de Reus et al. (
2000
),
15
Maring et al. (
2003
),
16
Bates et al. (
2002
),
17
Wagner et al. (
2009
),
18
Reid et al. (
2008
),
19
Haywood et al. (
2003b
),
20
Kim et al. (
2004
),
21
Zhou et al. (
2012
),
22
Quinn et al. (
2004
),
23
Clarke et al. (
2004
),
24
Kobayashi et al. (
2007
),
25
Chang et al. (
2010
),
26
Peters (
2006
),
27
Shao et al. (
2011
)
from the preferential settling of the large particles (e.g., Schütz et al.
1981
). The
latter gradient, however, is smaller. After 1,000 km or a few days of transport, no
modal diameter larger than 3 m particle diameter is detected and the change in
size distribution for mineral dust becomes very small (cf. also Reid et al.
2008
).
However, this does not mean that large particles cannot be transported over long
distances; for example, over Portugal, in the Caribbean, and over the Pacific Ocean,
particles measuring tens of micrometers were observed (Betzer et al.
1988
; Formenti
et al.
2001
; Wagner et al.
2009
).
In principle, Asian dust covers a similar range of observations like the
lifted/transported Saharan dust, so no different microphysical behavior for dust
dynamics should be expected. Only sparse data is available for other deserts, so no
conclusion can be drawn from them.
Figure
2.3
illustrates the difference between the desert aerosol and mineral
dust size distribution as defined previously. The mineral dust fraction of the total
size distributions in desert regions starts to decrease from unity at particle sizes
smaller than one micrometer. At 100 nm particle diameter, even comparatively
close
to
strong
dust
sources
most
of
the
airborne
particles
are
non-dust.
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