Soil Sand Resuspension

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Transport of continental dust to the ocean has been documented extensively in the Atlantic (Sect. 1), and the Asian continent has also been inferred as such a source [30, 68]. Continental dust is advected into the atmosphere from sands of desert areas and from exposed soils during tilling in agricultural regions. The organic compositions of the fine particulate matter of both types of sources are currently being characterized and their effects on atmospheric processes are under extensive study. Results from these studies should appear in the near future.

The organic compositions from some examples of sand and soil par-ticulate matter are illustrated here and compared with an aerosol sample (also compare Fig. 3a). The dominant organic tracers of desert sands are trace amounts of plant wax components comprising primarily n-alkanes and n-alkanols, with minor amounts of nonacosan-10-ol (XXVII), methyl alka-noates, sterols (I), and triterpenols (Fig. 8a [212]). The n-alkanes, n-alkanols, and n-alkanoic acid esters have the typical distributions and carbon number predominances of plant waxes. The organic tracers of desert sands are low in concentration and must be used in conjunction with mineralogical and trace metal compositions for source assessments. The lipid tracer compositions of different deserts are distinguishable and reflect primarily the regional climatic conditions affecting biomass fixation, with inputs of detritus mainly from grass waxes and secondarily from algae and woody plants.

Fig. 8 Representative TIC traces from GC-MS analyses of total extracts (silylated): a sand (fines, Gurbantunggut desert, Xinjiang, China), b soil from safflower field (San Joaquin Valley, CA, USA), c soil from tomato field (San Joaquin Valley, CA, USA), and d aerosol particulate matter (Gosan, Jeju Island, Korea, 11-12 April 2001) (compounds are labeled, numbers refer to carbon-chain length, see key for lipids)

Fig. 8 Representative TIC traces from GC-MS analyses of total extracts (silylated): a sand (fines, Gurbantunggut desert, Xinjiang, China), b soil from safflower field (San Joaquin Valley, CA, USA), c soil from tomato field (San Joaquin Valley, CA, USA), and d aerosol particulate matter (Gosan, Jeju Island, Korea, 11-12 April 2001) (compounds are labeled, numbers refer to carbon-chain length, see key for lipids)

Soils contain much higher concentrations of organic compounds than sands and those also comprise mainly lipids from higher vegetation. Soils contain the plant wax and biomarker compounds from the surficial or surrounding vegetation cover (e.g., resin acids, XXVIII-XXXI, from conifers in forest soil) [213]. Agricultural field soils contain the lipids from the crops, as well as the pesticide/herbicide residues remaining after use (e.g., DDE [212, 213]). The n-alkanols and n-alkanes are useful secondary tracers for fingerprinting soils, analogous to desert sands. However, these lipids have very high source concentrations in soils compared with trace levels in sands.

A novel and unique aspect is the presence of primary sugars (saccharides) in soils. The total extracts of agricultural soils from a safflower field and a tomato field are shown in Fig. 8b and c, respectively. The dominant compounds are sugars with only minor lipids and biomarkers. The most commonly encountered sugars are a- and ^-glucose, inositols (XXXII, several isomers), sucrose (disaccharide), and mycose (fungal disaccharide metabolite) [185]. Fructose, mannose, xylose, and other monosaccharides can also occur. Another aspect of soils is their enhanced contents of sterols and triter-penoids with depleted contents of the aliphatic plant wax lipids (i.e., alkanes and alkanols). The phytosterols (sitosterol, campesterol, and stigmasterol) are dominant, but cholesterol is also present, indicating a component from algae and fauna. Some soils can contain species-specific tracers, as, for example, ty-taraxasterol (XXXIII) in the safflower field (Fig. 8b). The presence of polar and water-soluble compounds in soil extracts indicates that both living and extracellular biomass was extracted. The enhanced sterol and triterpenol concentrations are probably due to their resistance toward biodegradation compared with the aliphatic plant wax lipids.

The impact of Asian dust on the northwestern Pacific region is currently under investigation and preliminary results have been reported [167]. A typical total ion current trace from the GC-MS analysis of a total extract (silylated) of aerosol particulate matter collected in Gosan (formerly Kosan) on Jeju (formerly Cheju) Island, Korea, is shown in Fig. 8d. A similar aerosol sample analysis is also shown in Fig. 3 for Sapporo. The high amounts of levoglucosan with mannosan and galactosan are tracers for smoke from biomass burning [126]. The primary sugars are a- and ^-glucose, xylitol, sorbitol, sucrose, and mycose. Xylitol and sorbitol are probably microbial/fungal alteration products of primary saccharides in soil particles introduced into the atmosphere.

A minor homologous series of n-alkanoic acids, ranging from C12-C30 with a strong even-to-odd carbon number predominance and a maximum at C16 (palmitic acid) was present, suggesting an input from terrestrial and marine biota, as well as from cooking. A trace of dehydroabietic acid further supports biomass burning. Significant amounts of dicarboxylic acids (e.g., glyceric, maleic, adipic, and benzene dicarboxylic acids) indicate secondary oxidation products [41]. The vascular plant wax components are minor and consist of the n-alkanes, n-alkanols, and nonacosan-10-ol, with traces of phy-tosterols. Thus, the primary inputs of organic compounds to these aerosols transported from Asia are (1) natural emissions from continental vegetation and marine lipids, (2) smoke from biomass burning, (3) soil resuspension due to agricultural activity, and (4) urban/industrial emissions from fossil fuel utilization, especially coal [39,40,167].

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