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Elemental composition of Tibetan Plateau top soils and its effect on evaluating atmospheric pollution transport
Chaoliu Li, Shichang Kang, Qianggong Zhang,
State Key Laboratory of Cryospheric Sciences Lanzhou 730000 China; Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Beijing 100085 China
E-mail: [email protected]; [email protected]
ID:GC41A-0847
The Tibetan Plateau is an ideal area to monitor
global transport of anthropogenic contaminants
besides Polar Regions because of its pristine
environment. So far, some research on aerosol
elements has been done across the TP in order to better
understand the atmospheric chemistry over the TP and
its relationship with other regions of the world.
Elements of anthropogenic origin transported from
Indian subcontinent have been recognized by
calculating element enrichment factors
(EFs)
of
a
aerosols. However, these results are still tentative and
mostly based on speculation due to neglecting the
potential effect of background geochemistry
characteristics of the TP derived soil dust. As one of
the youngest geological blocks in the world, the
b
c
geochemical characteristics of the TP are special with
some typical “pollution” elements (e.g. As) having
higher concentrations than average crustal values here.
This might strongly affect the aerosol EF results and
related speculations on pollutant identification over
the TP. Hence, it is necessary to establish a dataset of
element abundances of the TP soil dust.
Due to the western TP being the most important
dust source region of the TP, studied soil samples were
collected from this area during and measured for
element concentrations.
Results
7.0
< 20 m Fraction of Western TP Top Soils
Thar Aerosol
Sahara Aerosol
6.5
6.0
5.5
5.0
4.5
Samples/UCC
Introduction
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
La
Fig. 1 Sampling sites in the western Tibetan Plateau. Note solid
circles represent samples analyzed for both bulk and the <20 μm
fractions, open circles represent samples analyzed only for bulk part.
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Fig.3 UCC-normalized REE patterns of <20μm fractions of
west TP surface soils (circles), aerosol in Sahara desert
(triangles) and aerosol in Delhi of Thar desert (squares),
indicating the REE compositions of the TP soil, Thar dersert
and Sahara dust are different, which can be served as an
approach of distinguishing materials derived from them.
Conclusions
Fig.2 UCC-normalized elements for the median bulk
samples and the <20 μm fractions of the TP top soils,
indicating some elements of the Tibetan Plateau surface soil
are much higher than those of the upper continental crust
(UCC).
Concentrations of some elements such as B, As, Cs and
Bi in both bulk soils and the <20 μm fractions in the TP are
much higher than those of UCC. Thus, UCC concentrations
can not be used simply as reference values for evaluating
anthropogenic input for some trace elements by means of
enrichment factors. The data of the <20 μm fractions
presented here is suggested to be the local reference database
for investigating aerosol sources over the TP, especially
during the non-monsoon period when dust storms occur
frequently. REE characteristics of the TP soils could also
serve as an effective index for evaluating aerosol origins.
Therefore during future aerosol studies over the TP, REE
compositions can be used to determine the source region of
the aerosol and the database suggested in this study can be
applied.