Characterization of Individual Chinese Soil Particles
by the Combined Use of Low-Z Particle EPMA
and ATR-FT-IR imaging Techniques
BoHwa Kim, Hae-Jin Jung, Md Abdul Malek,
Young-Chul Song, and Chul-Un Ro*
Department of Chemistry
Inha University, KOREA
Introduction
◈ Airborne mineral dust
▶ The most abundant particulate matters in coarse atmospheric aerosols
▶ Arid and semi-arid areas, such as Saharan desert and central China, are major
sources of airborne mineral dust.
▶ Mineral dust aerosols can react with atmospheric gaseous pollutants such as
SOx and/or NOx → modified physicochemical properties of mineral dust
▶ Mineral dust can influence global climate directly by scattering and absorbing
solar radiations, and indirectly by serving as cloud condensation nuclei (CCN).
▶ Airborne mineral particles – from soil minerals
◈ Chinese soil particles at arid and desert areas
▶ Sources of Asian Dust particles
▶ Asian Dust particles can experience chemical modification during long range
transport to Korea.
▶ Detailed characterization of Chinese soil particles is important to understand
the characteristics of Asian Dust particles.
◈ Objectives
▶ Characterization of Chinese soils on a single particle level
by the combined use of two single particle analytical techniques such as
quantitative low-Z particle EPMA and ATR-FT-IR imaging
* Low-Z particle EPMA for the elemental concentration and morphology
(It has limitation to clearly identify different mineral types having similar composition
but different crystal structures)
* ATR-FT-IR imaging for the functional groups, molecular species, and crystal structure
▶ 2 loess samples and 4 desert samples
Sampling sites
Hungshan
Shaptou
Ganquan
Zhangbei
Minqin
Luochuan
Type
Site
Locations (Altitude)
loess
Luochuan
35.5°N, 109.2°E (1094 m)
desert
Shaptou
37.3°N, 105.0°E (1330 m)
loess
desert
desert
desert
Ganquan
Minqin
Hungshan
Zhangbei
36.4°N, 109.2°E (1029 m)
38.3°N, 102.5°E (1378 m)
42.1°N, 116.3°E (1266 m)
41.2°N, 114.5°E (1416 m)
◈ Previous studies on these Chinese soil samples
▶ Single-particle characterization of soil samples collected at various arid areas
of China, using low-Z particle electron probe X-ray microanalysis
(Kim et. al., Spectrochim. Acta B, 2006 )
* Analysis using SEM/EDX
- loess soils : aluminosilicates, CaCO3
- desert soils : aluminosilicates, SiO2
▶ Bulk and single-particle mineralogy of Asian dust and a comparison with its
source soils (Jeong, JGR, 2007)
* Analysis using XRD
- silt soil : rich-calcite, phyllosilicates
- sandy soil : quartz, plagioclase, K-feldspar
Experimental
◈ SEM/EDX and ATR-FT-IR imaging measurement
▶ Low-Z particle EPMA based on SEM/EDX
- SEM (JEOL JSM-6390) equipped with Oxford SATW ultrathin window
EDX detector
- Condition
• accelerating voltage : 10 kV
• measuring time : 30 sec
• beam current : 1.0 nA
• substrate : Ag foil
▶ ATR-FT-IR imaging
- Perkin Elmer Spectrum 100 FT-IR spectrometer
- Spectrum Spotlight 400 FT-IR optical microscope
- ATR accessory : Ge IRE crystal, diameter : 600 μm
- Mercury Cadmium Telluride (MCT) array detector
- pixel size : 1.56 μm
- spectral resolution of 4 cm-1 at the range of 680 to 4000 cm-1
Low-Z particle EPMA (Electron Probe X-ray
Microanalysis) for single particle analysis
1.
SEM-EDX (Scanning Electron Microscopy –
Energy Dispersive X-ray Spectrometer)
- Individual Particle Analysis
* shape and size : secondary / backscattered electron images
* chemical compositions : X-ray spectrum
2.
Ultra-thin window EDX for low-Z elements detection (e.g., C, N, O, F)
3.
Metallic collecting substrates for minimizing charging effect (e.g., Ag, Al)
4.
Monte Carlo calculation for Quantification
5.
Chemical speciation of aerosol particles – Expert System
Monte Carlo Calculation for Quantification
Measurement
Electron detector
Simulation
Electron beam
with 10keV
X-ray detector
1000
metal foil
SEM
Intensity(arb. units)
100
CaCO3 measured data
Ca
O
Simulated
C
10
1
0.1
0.01
0
1
2
3
4
5
6
7
8
9
10
X-ray Energy (keV)
Measured and simulated spectra for a
CaCO3 standard particle on a Be substrate
ATR-FT-IR imaging for single particle analysis
♦ ATR-FT-IR (Attenuated Total Reflectance-FT-IR Spectrometry)
- Individual Particle Analysis
* location : optical image
* functional groups, molecular species, and crystal structure : IR spectra
Dual detector
d = 600 ㎛
Visible radiation
▲ ATR imaging accessory
Cassegrain system
Motorized sample stage
Ge crystal – sample contact surface ▲
sample
IR radiation
◄ Ge crystal for imaging
Images for Luochuan loess soil particles
3
1
2
4
13
16
15
14
18
17
12
5
19
28
20
25
27
30
29
31
46
47
39
49 53
48
43 41
45
50 56 57
44
42 40
59 60
51
62
54 58 61
64
68
52
55
65
69
66
63
67
22
34
33
37
3
2
13
16
15 14
17
29
49
51
*
52
46
48
50 56 57
*
58
53 54
22
45
59
60
55
(c) PCA image
62
63
44
*
64
41 39
42
* 68
69
65
66
33
37
40
67
34
22
23
46
45
44
62
39
41
43
34
32
31
64
66
65
67
33
37
35
38
40
36
42
68
36
72
70 71
4
13 * 14
12
15
19
18
28
26
29
35
38
2* 1
17
24
32
43
21
20
25
3
16
* 21
20
31
47
61
9
23
25
27
30
*
*
8
7
19
18
26
28
*
11 10
12
11 10
19
70
69
71
72
(b) Optical image
6
5
4
8
9
63
(a) Secondary electron image
1
27
30
47
56
48
50
57
53
59
51
60
58
54
61
52
55
70 71
7
6
4 5
24
49
36
72
26
29
35
38
14
12
18
17
28
32
13
15
16
21
23
3
1
2
24
26
8
9
10
11
7
6
49
27
30
46
47
48
50 56 57
59
51 *53
58 61 60
54
* 55
52
6
5
9
*
11 10
20
23
24
25
63
44
**
62
*
65
21
* 22
32
31
45
*
8
7
43
41
42 40
64
66
39
37
38
33
35
36
* 68
69
*
34
72
70
* * 71
67
(d) Transmission signal Image at single wavenumber of 1000cm-1
X-ray spectra and elemental concentrations of typical loess soil particles
Elemental Concentration (at. %)
Si
C 7.3 Al 2.1
O
O 40.3 Si 46.4
Ag-L
Mg 0.8 Ca 3.0
Al
C Mg
O
C
Ca
Elemental Concentration (at. %)
Mg
C 3.0 Al 14.0
Si
O 47.5 Si 19.0
Mg
7.6 K 1.6
Ag-L
C
K
Fe 6.5
Fe
Al
(d) Montmorillonite/MgCO3/Fe
Elemental Concentration (at. %)
C 14.4 Al 3.9
O
Si
O 54.1 Si 10.7
C Al Ag-LCa
Mg 1.1 Ca 14.1
Mg
Ag-L
(a) Quartz/Calcite
O
Elemental Concentration (at. %)
C 15.7
O 65.7
Ca
Ca 18.6
(b) Calcite
O
(c) Montmorillonite/Calcite
Elemental Concentration (at. %)
C 12.6 Al 13.3
Ag-L
C
O 49.9 Si 18.5
Mg Si K
Ca
Mg 1.5 K 1.7
Ca 2.6
Al
Elemental Concentration (at. %)
C 12.5 Al 12.1
Al Ag-L
Na
O 33.1 Si 34.9
Si
C
Na 4.8 Ca 2.0
Ca
(e) Muscovite/Calcite
(f) Na-feldspar/Calcite
O
ATR-FT-IR spectra of typical loess soil particles
797, 779 : Si-O
1383 : CO32-
(a) Quartz/Calcite (Ganquan)
1062 : Si-O
1176: Si(Al)-O (Heulandite)
(b) Calcite (Luochuan)
1398
834: AlMg-O
(c) Montmorillonite/Calcite (Luochuan)
796
1412
871 : CO321008: Si-O
ATR-FT-IR spectra of typical loess soil particles
3412 : OH
1478, 1428 : CO32776 : Si-Si
970: Si-O
(d) Montmorillonite/MgCO3/Fe (Ganquan)
746 : Si-O
(e) Muscovite/Calcite (Luochuan)
1434 : CO32-
1436 :
912 : AlAl-OH
CO32-
984
822 : Al-O
870 : CO32-
746
(f) Na-feldspar/Calcite (Ganquan)
788 : Si-Si
1118, 1084 : Si-O
988
866
X-ray spectra and elemental concentrations of typical desert soil particles
O
C
Elemental Concentration (at. %)
Si
C 2.5 Al 2.6
O 63.5 Si 28.5
Al
Ag-L
(a) Cristobalite
Elemental Concentration (at. %)
C 3.8 Al 8.6
O
Si
O 57.6 Si 21.5
Al
Na
Na 5.5
C
Elemental Concentration (at. %)
O
Si
C 17.4 Mg 1.5
Al
Ag-L
O 46.3 Al 5.9
C
Mg
Na 0.4 Si 12.4
Ca
Ca 1.1
Fe
Fe 14.1
Fe
(b) Montmorillonite/Fe
Elemental Concentration (at. %)
C 9.4 Al 11.7
AlSi Ag-L
O 54.9 Si 17.8
C Mg
K
Mg 1.3 K 3.7
O
(c) Montmorillonite
O
Elemental Concentration (at. %)
C 2.6 Al 21.2
Si K
O 40.7 Si 25.4
Mg Ag-L
Mg
1.1 K 7.5
C
Al
Ag-L
(d) Na-feldspar
Elemental Concentration (at. %)
C 10.5 Al 16.9
Si
Al
O 50.5 Si 19.2
C Mg
Mg 1.0 Fe 1.0
Ag-L
O
(e) K-feldspar
(f) Muscovite
ATR-FT-IR spectra of typical desert soil particles
794 : Si-O
1050 : Si-O
(a) Cristobalite (Shaptou)
(b) Montmorillonite/Fe (Hungshan)
772
1042 : Si-O
(c) Montmorillonite (Zhangbei)
1638 : H2O
760 : Si-Si
1638 : OH
(feldspar)
1004 : Si-O
800 : Si-O
ATR-FT-IR spectra of typical desert soil particles
795, 760 : Si-Si
(d) Na-feldspar (Shaptou)
1026, 974 : Si(Al)-O
1152, 1093 : Si-O
735, 728 :
Si(Al)-Si
852 : AlMg-OH
(montmorillonite)
(e) K-feldspar (Minqin)
1112 : Si-O
733
776 : Si-Si
(f) Muscovite (Minqin)
1031, 1003 : Si(Al)-O
754 :
Al-O-Si
3605 : OH
916 : AlAl-OH
980 : Si-O
821 : Al-O
Relative abundances of mineral types observed in Chinese soils
Relative abundances (%)
Loess
Desert
ite
c
l
Ca
Si
ite
ies
ies
ies
ies
ie s
ies
c
c
c
c
c
l
c
c
e
e
e
e
a
e
e
/C
sp
sp
sp
sp
sp
sp
e
r
t
2
e
e
e
e
g
i
t
O
t
a
i
it
it
n
n
ni
Si
at
ul
sp
ni
ov
o
i
c
p
l
d
illo
c
i
l
l
a
r
i
t
A
m
o
us
Fe
or
on
m
er
M
t
m
c
V
t
n
n
Fe
Mo
Mo
O2
lc i
a
/C
te
Mineral types
r
he
t
O
s
Conclusions
◈ In loess soils, the most abundant particles are observed to be silicates minerals
mixed with calcite.
◈ Desert soils have higher content of SiO2 than the loess soils do.
◈ Low-Z particle EPMA and ATR-FT-IR imaging techniques provide complimentary
information on the physicochemical characteristics of the same individual
soil particles.
◈ low-Z particle EPMA for the information on the morphology and elemental
concentrations
◈ ATR-FT-IR imaging for the information on the functional group, molecular species,
and crystal structure