Geochemical sources

The salt particles from the oceans are hygroscopic and under humid conditions these tiny NaCl crystals attract water and form a concentrated solution droplet or aerosol. Ultimately, this process can take part in cloud formation. The droplets can also be a site for important chemical reactions in the atmosphere. If strong acids (Box 3.3) in the atmosphere, perhaps nitric acid (HNO () or sulphuric acid (H2S04), dissolve in these small droplets, hydrogen chloride (HC1) can be formed. It is thought that this process is an important source of HC1 in the atmosphere  

ITSOyin aerosol) NhCl(in aerosol) t I ICL g i + ISlaUSCUim aerosol) eC[n. 3.6 

Incoming meteors also inject particles into the atmosphere. This is a very small source compared with wind-blown dust or forest fires, but meteors make their contribution to the upper parts of the atmosphere where the gas is at a low density. Here, a small contribution can be particularly significant and the metals ablated from incoming meteors enter a series of chemical reactions. 

It is important to realize that the volcanic source is a very discontinuous one, both in time and space. Large volcanic eruptions are infrequent. It may be that years pass without any really major eruptions and then suddenly more material 

Acids and bases are an important class of chemical compounds, because they exert special control over reactions in water. Traditionally acids have been seen as compounds that dissociate to yield hydrogen ions in water  

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The chemical evolution of groundwater within the study area was explained by considering the geologic history of the region since the Pleistocene, the geochemical sources of dissolved constituents, and the processes of groundwater flow and mixing. 

The basis for the iron sulfide system as a first and archaic version of a primordial forerunner of a metabolic pathway is a chemical reaction. Under standard conditions, FeS and H2S from submarine geochemical sources provide reducing power of about —620 mV by forming pyrite FeS2. 

The macroelements K, Ca, Na, Mg and Fe detected in transplants of U. hirta and H. physodes derive mainly from geochemical sources and are important constituents of... 

Anawar, H. M., J. Akai, K. M. G. Mostofa, et al. 2002. Arsenic Poisoning in Groundwater Health Risk and Geochemical Sources in Bangladesh. Environment International 27 597-604. 

Geochemical studies of sulfate ia streams have beea approached ia various ways. For example. Ref. 17 is a review of Hterature oa sources of sulfate ia the dissolved loads of streams, especially ia areas where developmeat effects are likely to be stroag. It was coacluded that for North America as much as 60% of the average yield of sulfate carried to the ocean is related to human activities. This study assigned a higher proportion of the total yield of sulfate ia European streams to human sources, but for other continents it was thought the effects of human activities to be relatively minor. 

Andreae, M. O. (1986). The ocean as a source of atmospheric sulfur compounds. In "The Role of Air-Sea Exchange in Geochemical Cycling" (P. Buat-Menard, ed.). Reidel, Dordrecht. 

Identification of sources of analytical bias in method development and method validation is another very important application of reference materials in geochemical laboratories. USGS applied simplex optimization in establishing the best measurement conditions when the ICP-AES method was introduced as a substitute for AAS in the rapid rock procedure for major oxide determinations (Leary et al. 1982). The optimized measurement parameters were then validated by analyzing a number of USGS rock reference samples for which reference values had been established first by classical analyses. Similar optimization of an ICP-AES procedure for a number of trace elements was validated by the analysis of U S G S manganese nodule P-i (Montaser et al. 1984). 

Modern geochemical studies use data for a much larger suite of elements, determined at much lower concentrations, to model the tectonic movements of continental plates, and to understand the sources of magma generated in that process (e.g. Lightfoot 1993 Sutcliffe 1993). The key elemental suites include the incompatible ... 

While over the past ten years, our ability to measure U-series disequilibria and interpret this data has improved significantly it is important to note that many questions still remain. In particular, because of uncertainties in the partition coefficients, fully quantitative constraints can only be obtained when more experimental data, as a function of P and T as well as source composition, become available. Furthermore, the robustness of the various melting models that are used to interpret the data needs to be established and 2D and 3D models need to be developed. However, full testing of these models will only be possible when more comprehensive data sets including all the geochemical parameters are available for more locations and settings. 

Stracke A, Salters VJM, Sims KWW (1999) Assessing the presence of gamet-pyroxenite in the mantle sources of basalts through combined hafnium-neodymium-thorium isotope systematics. Geochem Geophys Geosyst L1999GC000013... 

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