Dilution, test atmospheres

Fossil fuel emissions alter the isotopic composition of atmospheric carbon, since they contain no C and are depleted in C. Releasing radiocarbon-free CO2 to the atmosphere dilutes the atmospheric C content, 3delding lower C/C ratios ("the Suess effect"). From 1850 to 1954 the C/C ratio in the atmosphere decreased by 2.0 to 2.5% (Fig. 11-23) (Suess, 1965 Stuiver and Quay, 1981). Then, this downward trend in C was disrupted by a series of atmospheric nuclear tests. Many large fission explosions set off by the United States with high emission of neutrons took place in 1958 in the atmosphere and the Soviet Union held extensive tests during... 

Examples of such procedures are making dilutions (not all components of the mixture may be equally soluble or miscible with the vehicle) and generating either vapors or respirable aerosols (not all the components may have equivalent volatility or surface tension, leading to a test atmosphere that contains only a portion of the components of the mixture). 

Dilution—A cylinder of the compressed gas is fitted with a metering apparatus (regulator and/or critical flow orifice) and the effluent stream is injected directly into the dilution system. The flow rates of the analyte can be calibrated and the concentration of each test atmosphere can be calculated from the known dilution air flows. 

The simulated test atmosphere with high levels of contaminant (2 to 5ppm) were analyzed by both the in-line GC (in the primary dilution module) and by direct injection of air taken from the sampling port (in the secondary dilution module). The purpose of the latter was to establish the reliability of the in-line GC. The in-line monitor was particularly important in test atmosphere with low contaminant concentration because in this case, direct injection of the air is not feasible. Table I compares the results obtained by the in-line GC and direct air injection for ethylene oxide and acetone. 

We have developed and used a number of generation techniques for producing test atmospheres for the evaluation of methods of collection of ambient air samples. These methods are applicable to many compounds and, with modification, can be extended to cover most materials. In principle, several compounds may be generated simultaneously with these techniques. Testing over an appropriate concentration range is easily accomplished using the dilution system we have designed. 

Provision and use of appropriate health surveillance, e.g. for signs of dermatitis, asthma, effects of specific solvent exposures. Full use of any spray booth, enclosure, exhaust ventilation or dilution systems, and automatic handling equipment. (The efficiency of all local exhaust ventilation and other control systems should be maintained, and checked by testing.) Where appropriate, atmospheric monitoring of airborne pollution levels. 

A mass of evidence seems to confirm that the mixing rate of radiocarbon in the atmosphere is rapid, and that with respect to its radiocarbon content the atmosphere can be considered as a homogeneous entirety. The contamination of samples with matter from an extraneous source can nevertheless invalidate this assumption. Two types of contamination can be differentiated physicochemical contamination and mechanical intrusion. There are two forms of physicochemical contamination. One is due to the dilution of the concentration of radiocarbon in the atmosphere by very old carbon, practically depleted of radiocarbon, released by the combustion of fossil fuel, such as coal and oil. The other is by the contamination with radiocarbon produced by nuclear bomb tests during the 1950s and later in the twentieth century. The uncertainties introduced by these forms of contamination complicate the interpretation of data obtained by the radiocarbon dating method and restrict its accuracy and the effective time range of dating. 

There would be, however, a considerable discrepancy between the model-calculated dilution factor and the dilution factor required if the biospheric C02 input were of comparable size as the fossil C02 input as stated by biologists [43]. For a discussion of this question see also Oeschger et al., [39]. Thirdly, we calculate the 14C dilution corresponding to the CO increase. In 1950, before the nuclear weapon tests, the integrated C02 production amounted to about 10 percent of the preindustrial atmospheric C02 content. If there had been no exchange with other reservoirs, a decrease of the 14C/C ratio by 10 percent would have resulted. Tree-ring 14C measurements indicated, however, a decrease by only about 2 percent. Again we calculate the system dilution. In a first approximation 4 and s are set equal to one and we obtain... 

Catalytic tests of n-pentane oxidation were carried out in a laboratory glass flow-reactor, operating at atmospheric pressure, and loading 3 g of catalyst diluted with inert material. Feed composition was 1 mol% n-pentane in air residence time was 2 g s/ml. The temperature of reaction was varied from 340 to 420°C. The products were collected and analyzed by means of gas chromatography. A FlP-l column (FID) was used for the separation of C5 hydrocarbons, MA and PA. A Carbosieve Sll column (TCD) was used for the separation of oxygen, carbon monoxide and carbon dioxide. 

---