The Two Signatures of Chinese
Dust Storms in Beijing
Three major dust sources + Loess Plateau
Northern lowdust deserts
Northwestern
deserts
Northern highdust deserts
Loess area
Main transport pathways
Takla
Makan
Gobi
Rocky
desert with
less salts.
Sandy desert
with abundant
salts
(chlorides,
sulfates,
carbonates).
(Makra L. et
al, 2002)
(Sun, J. 2002)
The 6 dust storms and their 3 types
Site: BNU
12000
TSP
10000
I
8000
DS3
II
6000
II
4000
II
DS4
III
DS1
DS5
DS2
III
DS6
2000
950 µg m-3
4-27-02
4-23-02
4-20-02
4-14-02
4-12-02
4-10-02
4-8-02
4-7-02
4-4-02
4-1-02
3-25-02
3-22-02
3-20-02
3-19-02
3-30-01
3-22-01
3-15-01
3-9-01
3-3-01
3-2-01
0
Dust episodes defined by meteorological reports, air pollution indices, and our TSP data.
Ca vs. Al
DS I
af ter DS I
DS II
af ter DS II
DS III
NDS
1000
Ca (ug/m3)
100
10
Ca/Al=1.2
1
I
Ca/Al=0.39
II
Ca/Al=0.23*
0.1
0.1
1
10
Al (ug/m3)
100
1000
S vs. Al
DS I
af ter DS I
DS II
af ter DS II
DS III
NDS
100
S (ug/m3)
10
1
0.1
S/Al=0.072
I
S/Al=0.030
II
S/Al=0.013**
0.01
0.1
1
10
Al (ug/m3)
100
1000
Co vs. Al
DS I
af ter DS I
DS II
af ter DS II
DS III
NDS
1
Co (ug/m3)
0.1
0.01
0.001
Co/Al=0.00041
I
Co/Al=0.00025
II
Co/Al=0.00019
0.0001
0.1
1
10
Al (ug/m3)
100
1000
Sr vs. Al
DS I
af ter DS I
DS II
af ter DS II
DS III
NDS
10
Sr (ug/m3)
1
0.1
I
0.01
Sr/Al=0.0042
II
Sr/Al=0.0030
Sr/Al=0.0025*
0.001
0.1
1
10
Al (ug/m3)
100
1000
Sc vs. Al
DS I
af ter DS I
DS II
af ter DS II
DS III
NDS
1
Sc(ug/m3)
0.1
0.01
0.001
Sc/Al=0.00016*
I
Sc/Al=0.00015
Sc/Al=0.00012
II
0.0001
0.1
1
10
Al (ug/m3)
100
1000
Ca vs. S
DS I
af ter DS I
DS II
af ter DS II
DS III
NDS
1000
Ca (ug/m3)
100
10
Ca/S=17*
I
Ca/S=16
1
II
Ca/S=15
0.1
0.1
1
10
S(ug/m3)
100
1000
Back trajectories for the two types
of episodes
DS3
I
DS4
II
Fig.1. Back trajectories for air parcels that arrived at Beijing during DS3 (left) and DS4 (right)
caculated from NOAA (http://www.noaa.gov).
Elements that don’t work
Fe, Ti, V, Mg, Na, Zn, Cu
Fe vs. Al
DS I
af ter DS I
DS II
af ter DS II
DS III
NDS
1000
Fe (ug/m3)
100
10
1
Fe/Al=0.062
I
II
Fe/Al=0.055
Fe/Al=0.045*
0.1
0.1
1
10
Al (ug/m3)
100
1000
Ti vs. Al
DS I
af ter DS I
DS II
af ter DS II
DS III
NDS
100
Ti (ug/m3)
10
1
0.1
Ti/Al=0.067
I
Ti/Al=0.060
II
Ti/Al=0.057*
0.01
0.1
1
10
Al (ug/m3)
100
1000
V vs. Al
DS I
af ter DS I
DS II
af ter DS II
DS III
NDS
10
V (ug/m3)
1
0.1
0.01
V/Al=0.0016
II.I
V/Al=0.0012*
0.001
0.1
1
10
Al (ug/m3)
100
1000
Mg vs. Al
DS I
af ter DS I
DS II
af ter DS II
DS III
NDS
1000
Mg (ug/m3)
100
10
1
Mg/Al=0.23
I
Mg/Al=0.21
II
Mg/Al=0.12*
0.1
0.1
1
10
Al (ug/m3)
100
1000
Mn vs. Al
DS I
af ter DS I
DS II
af ter DS II
DS III
NDS
10
Mn (ug/m3)
1
0.1
0.01
Mn/Al=0.0090
II.I
Mn/Al=0.0088*
0.001
0.1
1
10
Al (ug/m3)
100
1000
Na vs. Al
DS I
af ter DS I
DS II
af ter DS II
DS III
NDS
1000
Na (ug/m3)
100
10
1
Na/Al=0.25
II
Na/Al=0.21
I
Na/Al=0.15*
0.1
0.1
1
10
Al (ug/m3)
100
1000
Zn vs. Al
DS I
af ter DS I
DS II
af ter DS II
DS III
NDS
10
Zn (ug/m3)
1
0.1
0.01
Zn/Al=0.0020
I,II
Zn/Al=0.0012*
0.001
0.1
1
10
Al (ug/m3)
100
1000
Cu vs. Al
DS I
af ter DS I
DS II
af ter DS II
DS III
NDS
10
Cu (ug/m3)
1
0.1
0.01
Cu/Al=0.00070
I
Cu/Al=0.00034*
0.001
0.1
1
10
Al (ug/m3)
100
1000
Ratio
DS I/DS II
Ca/Al
3.2±0.3
S/Al
2.4±0.3
Co/Al
1.61±0.11
Sr/Al
1.37±0.07
Sc/Al
1.30±0.04
Fe/Al
1.14±0.06
Ti/Al
1.12±0.07
V/Al
1.08±0.09
Mg/Al
1.07±0.07
Mn/Al
1.01±0.05
Na/Al
0.82±0.13
Cl-/Al
0.60±0.24
T-tests (two-tailed)
Ratio
DS I vs DS II
DS II vs NDS
Ca/Al
S/Al
Co/Al
Sr/Al
0.000
0.000
0.001
0.001
0.000
0.000
0.000
0.000
Sc/Al
0.000
0.001
Fe/Al
Ti/Al
V/Al
Mg/Al
Mn/Al
0.066
0.124
0.376
0.355
0.830
0.032
0.182
0.020
0.000
0.000
Why these six elements?
Maybe just ionic substitution for
Ca++ in the gypsum matrix
Principles of ionic substitution
• Free substitution when:
– ionic radii are within about 15%
– charges differ by zero or one unit.
• The next slide shows the ions that can freely
substitute for Ca in gypsum.
• They are Na (which will go to halite instead),
Sr, the REE (not measured here), and Sc.
• Except for Co, these cations match the
observed cationic enrichments in the high-Ca
signal.
Ionic radii main
1.8
Cs
1.6
Rb
K
Ionic radius, A
1.4
Ba
Pb
Sr
1.2
1
Na
0.8
Li
0.6
0.4
0.2
La
Ca
REE
MnZn
Sc
In
Co NiCu
Fe
Mg
Ga
Al
Be
B
U
ZrHf
Ti
Mn
GeSe
Si
NbTa
V
P
S
C
0
0
1
2
3
4
Charge
5
6
7
Previous attempts to find chemical tracers
• Yang D. et al. (1997) In Chinese
– Concentrations of 12 elements from five sites
between Beijing and source areas, but no
explicit characterization of sources.
• Zhang X. et al. (1996, 1997)
– Four-element tracer system (Al, Fe, Mg, Sc) that
reportedly differentiated three desert sources in
China (NW, N, NE). S not measured, and Ca
eliminated because of “postdepositional effects.”
Previous attempts, cont’d
• Zhang X. et al. (2003)
– NW deserts have 50% higher Ca, Fe, K, and Mg, and
20% lower Si, Al, Mn, and Ti than N deserts.
• Nakano et al. (2004)
– Sr/Nd isotopic data from soils used to claim that
contemporary dustfall on Beijing comes more from nearby
soils (<200 km) than from deserts or Loess Plateau.
– Direct dustfall not measured.
• Xuan J. (2005)
– Emissions of Fe, Al, K, Mg, Mn, Na, Ca, and Ti in dust
calculated from surface soils of six sources (three in
Mongolia and three in China). X/Al ratios 14%–36%
higher from NW deserts than from N deserts, with Mn and
Ca the highest and Fe and Ti the lowest.
Summary
• The main tracer system previously suggested (Fe/Al,
Mg/Al, Sc/Al) does not work after transport to Beijing.
• Instead, a five-ratio system (Ca/Al, S/Al, Sr/Al, Co/Al,
Sc/Al) distinguishes the Takla Makan from the Gobi.
• The enriched Ca and S of the upper line agree with
the enrichment of gypsum and other salts in the
Takla Makan (Zhang et al 2003; Makra et al., 2002;
Okada 2004; Chinese Soil Atlas, 1994).
– Rivers from surrounding mountains drain into the Tarim
Basin and dry up there, depositing their salts (NaCl,
CaCO3, CaSO4, etc.).
• The co-enrichments of Sr, Co, and Sc are consistent
with ionic substitution for Ca in gypsum of the Takla
Makan.
• These results also provide a way to deal
with the high Ca from Beijing.
– The two sources can be differentiated by
S/Al or Ca/S.
– Dust storms from Xinjiang replace the high
Ca of Beijing (construction activities?) with
high Ca from the Takla Makan Desert.
– Thus the aerosol really does change when
a dust storm arrives.
The straightness of the 1:1 lines over
an episode
• The straightness of the 1:1 lines over two orders
of magnitude of concentration means that the
dust storms remain a single material throughout
the episode. This in turn implies at least two
things:
– (1) No significant SO2 is converted to sulfate on the
surface of the dust as it enters Beijing. This agrees
with the findings of Zhang D. et al. for Qingdao (AE,
2003) and Song et al. for ACE-Asia (AE, 2005).
– (2) The signal from the dust overwhelms the
signal of local Beijing dust, even down to very
low concentrations.
• This is consistent with the “clear-out” phase in dust
storms (Guo et al, 2004), which can be stronger and
last longer than first thought.
• It further means that the wind speeds during dust
storms in Beijing, much lower than those at the
source, are too low to resuspend much dust in
Beijing.
• This is particularly so when the first stage of a dust
storm is falling dust, which usually has very low wind
speeds because it arrives ahead of the cold front.
Some thoughts about the future
Possible areas of research
• Verifying the two signatures with samples
from other times and places.
• Searching for other signatures, say from the
northern low-dust area or from Kazakhstan
(northwest of the Takla Makan).
• Explaining the two signatures.
• Tracking dust clouds by means of their
signatures.
• Using the signatures to interpret existing
sets of data.
Explaining the two signatures
• Dust storms may come from small “hot spots” in
deserts rather than from evenly over the entire
surface.
• In Africa (the Sahara), these hot spots are
“wadis,” or ephemeral dried river channels and
lake bottoms.
• Does the same thing hold for Chinese deserts?
• Prospero reports that the early stages of dust
storms from the Gobi are composed of narrow
plumes from hot spots that later diffuse into a
broad dust cloud. (As seen from satellite photos).
Identifying the Chinese hot spots
• Examine satellite photos from early stages
of dust storms in the Gobi and the Takla
Makan.
– See whether hot spots can be verified.
– If so, see whether they occupy consistent
locations.
– If so, see whether those locations can be
identified on maps.
– If so, are they wadis or something else?
Determining properties of hot spots
• Go to the hot spots and sample their soil.
• Compare the hot spots with each other and with
the surrounding soil (and with the average desert
soil).
– Average desert soil may be available from the literature.
– Data on hot spots may also be available somewhere,
but I am guessing not.
• May have to take multiple samples along a dried
river bed—don’t know how many yet.
• Also don’t know how many hot spots have to be
sampled.
Determining properties of aerosol
blown out of hot spots
• Don’t yet know how best to do it.
• Sample at the very beginning of dust
storm?
• Create aerosol from the soil in a wind
tunnel?
• Create the aerosol right there in the desert?
(Jinghua’s idea)
The possible stages of fractionation
• Hot spots vs. deserts.
• One hot spot vs. another.
– Salt in soils promotes lifting.
• Aerosol vs. soil in hot spots.
• Aerosol vs. aerosol-sized soil in hot spots.
– Some minerals may be lifted more effectively
than other minerals.
• Depletion of coarse aerosol during
transport.
The End