Remote atmospheric dust examples

Since the majority of the elements in surface dust arise from deposited aerosol and added soil it is not surprising to find strong linear relationships between the concentrations of the elements in an atmospheric dust and street or house dust. This is illustrated by the two examples given in Fig. 8 for remote house dust vs urban atmospheric dust and street dust vs rural atmospheric dust. As discussed above crustal/soil material is a major component of atmospheric dust and the soil based elements in the atmospheric dust are Al, Ca, Fe, Mg, Mn, Ni, K, Si and Ti. The elements As, Br, Cd, Cl, Co, Cu, Pb, Rb, Se, V, and Zn are, on the other hand, enriched in atmospheric dust. The same elemental distribution applies to surface dust, but in this case their concentrations (compared on a mass basis) are reduced presumably due to dilution with soil. However, the elements enriched in the atmosphere remain enriched in the surface dusts. 

Where atmospheric Pb levels are high, this pathway is significant in terms of PbB contribution. Note that in this modeled depiction, a causality chain and pathway flow within that chain are implicitly required and explicitly depicted. For example, environmental Pb input to the human receptor goes from remote sources to proximate pathway. Hand Pb is proximate to the intake and uptake of Pb by children and lead workers with dusty Pb conditions in the workplace. This approach provides considerable mechanistic information on the specifics of how Pb exposures occur. Cross-sectional SEM models, the more typical form of this approach, probe the relationships among several environmental pathways simultaneously, as would be the case above linking soil and dust Pb to Pb via soil to dust, dust to blood, and the direct path of soil Pb to blood Pb. 

CMorinated pesticides enter the atmosphere primarily through spray drift during application, wind-blown dusts, and volatilization from treated surfaces. Heavy use of chlorinated pesticides generally means that spray drift is the most important means of entry to the atmosphere. In general, application by airplane results in more drift than application by ground equipment, and dusts drift more than sprays. For example, ZDDT particles measuring 2 /rni in diameter drifted about 35 km compared to 70 m for 50 jum droplets (Spencer, 1975). Wind-blown dusts are the most important source of entry to the atmosphere in areas where the use of chlorinated pesticides is either limited or curtailed. The dust source category will continue to contribute substantially to the world-wide redistribution of pesticides, particularly DDT and its derivatives, for many years to come. This partially accounts for the presence of detectable levels of pesticides in the sediments of remote Arctic lakes. 

The rate at which sulfur dioxide, released into the atmosphere, becomes oxidized to the +6 oxidation state to form sulfuric acid depends on the following conditions humidity, the amounts of dust particles, and the concentrations of transient radicals present, for example OH. Sulfur dioxide does not react directly with molecular oxygen and/or the water vapour in the air. Some of the principal mechanisms identified as contributing to its oxidation are outlined in this section and depicted in Figure 5.1. These reactions proceed slowly, the half-lives may be several hours or days, during which the sulfur may travel in moving air masses (wind) for hundreds of kilometres from the point of release. The sulfuric acid, mainly dissolved in raindrops, may then be precipitated to cause pollution at areas remote from the point of generation and predominantly downwind. 

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