Atmospheric pathway

Comparison of Figs 13-6a and 13-6b clearly demonstrates the degree to which human activity has modified the cycle of sulfur, largely via an atmospheric pathway. The influence of this perturbation can be inferred, and in some cases measured, in reservoirs that are very distant from industrial activity. Ivanov (1983) estimates that the flux of sulfur down the Earth s rivers to the ocean has roughly doubled due to human activity. Included in Table 13-2 and Fig. 13-6 are fluxes to the hydrosphere and lithosphere, which leads us to these other important parts of the sulfur cycle. 

Graham, W. F. (1977). Atmospheric pathways of the phosphorus cycle. Ph.D. Thesis, University of Rhode Island. 

MEPAS uses mathematical algorithms and a coupled pathways analysis to predict the potential for contaminant migration from a waste site to important environmental receptors. Groundwater, overland, surface water (e.g., rivers and wetlands), and atmospheric pathways are considered. Using the contaminant transport predictions, computed... 

Droppo, J. G. Jr. Buck, J. W. "Characterization of the Atmospheric Pathway at Hazardous Waste Sites." Proc. DOE Model Conf.. 1988, pp 1-11. 

A very significant peculiarity of the atmosphere is that so-called self-cleaning processes take place within the air. Due to these processes even those trace constituents which have no other chemical or biological sinks are relatively quickly removed from the air. Hence these removal mechanisms are of great importance for the control of the atmospheric pathways of some trace gases and aerosol particles (see Chapter 5). 

In this book air chemistry is defined as a branch of atmospheric science dealing with the atmospheric part of the biogeochemical cycle of different constituents. In other words this means that we will deal mainly with the atmospheric pathways of those components that are involved in the mass flow between the atmosphere and biosphere, as well as in chemical interactions between the air and the other media of our environment (soils, oceans etc.). It follows from this definition that, on the one hand, our discussion will be restricted to the troposphere and the stratosphere4 and, on the other hand, the photochemistry of the upper layers, the subject matter of the aeronomy (e.g. Nicolet, 1964), will be omitted. This separation of the (photo) chemistry of the lower (troposphere and stratosphere) and upper atmosphere makes it possible to give a more compact treatment of our problem, including the global anthropogenic effects due to the increase of air pollution. 

It is assumed that the majority of carbon monoxide is removed from the atmosphere by these reactions. Seiler (1974) hypothesizes that the yearly CO loss in the troposphere due to [3.5] and [3.7], is (1940-5000) x 1061 yr-1 The corresponding figure for the stratosphere is estimated to be 110 x 106 t yr-1 (see Table 7). In contrast, Warneck (1974) speculates that the global atmospheric strength of this sink is much smaller than the Seiler s figure. Finally, according to the calculations of Ehhalt and Schmidt (1978) about (1500-2900) x 1061C02 is produced yearly from CH4 by reaction steps [3.4], [3.2], [3.5] and [3.7]. On the basis of these data for the schematic representation of the atmospheric pathways of carbon a value of 2800 x 106 t yr 1 expressed in C02 will be accepted (see Fig. 8, p. 46) for this sink term. 

Atmospheric pathways of carbon compounds. Sote. CH4 released by paddy fields isconsidered biogenic... 

Atmospheric pathways of nitrogen compounds. Note NH, released from domestic animal urea is considered biogenic and not pollution... 

On the right-hand side of Fig. IS the atmospheric pathways of NH3 are plotted. Values of different terms are based on the references mentioned. In the figure, NH3 and NH4 burdens are also given. All numbers are expressed in nitrogen equivalents. In the total deposition value, a dry deposition of 10 x 10b t yr-1 is postulated. It should be noted that the accuracy of the values is not better than a factor of 2 or 3. It follows from these data that the residence time of NH3 in the atmosphere is around 5 days. 

Since Herring Gulls and coho salmon accumulate these residues from their common food supply, it seemed logical to consider the human exposure routes thoroughly, particularly the food supply. An early study by Bennet 2 ) followed total non-occupational environmental exposure of PCB to humans. This study showed that for PCB the atmospheric pathway contaminates plants directly, livestock indirectly, and ultimately contributes the major human environmental dosage of PCB. Exposure from drinking water and the atmosphere directly are inconsequential relative to food exposure. A more recent modelling effort (1J7) for... 

Liu CL, Zhang J (1996) Transport of particulate heavy metals towards the ocean via riverine and atmospheric pathways. Mar Environ Sci 15(4) 68-76 (in Chinese with English abstract)... 

D. Whelpdale, Atmospheric Pathways of Sulphur Compounds, MARC report 7, 1978. 

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous hydrophobic organic contaminants in the environment. They tend to be associated with particles and are widely transported by flooding and atmospheric pathways, resulting in elevated concentrations in sediments/soils. Coal and coal-derived particles in natural sediments/soils can act not only as strong sinks for the PAHs, but also as veiy important sources of PAHs in sediments/soils. The understanding of the mobility of these contaminants from the sediments/soils, especially the sequestration of PAHs by coal and coal-derived particles is very important, because they can control the transportation, bioavailability, degradation and hence the potential risk of these contaminants in the enviromnent. 

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