Elemental composition of Tibetan Plateau top soils and its effect on evaluating atmospheric pollution transportChaoliu 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 ChinaE-mail: Shichang.kang@itpcas.ac.cn; lichaoliu@itpcas.ac.cn

ID:GC41A-0847

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Introduction Results

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 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 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.

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.

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.

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.

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

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< 20 m Fraction of Western TP Top Soils Thar Aerosol Sahara Aerosol

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).

Conclusions