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Carbon background concentration

The relative humidity thus measured was 32% and the carbon dioxide concentration was 360 ppm. Trade (B) is a blowup of the 2060-2260 cm l region, where absorption due to CO and N2O can be recognized. Typical background concentrations of CO (0.28 ppm), N2O (0.45 ppm) and as well CH4 (1.6 ppm) were measured. In addition, a trace amount of HCl (0.12 ppm) was detected, as will be described in detail in subsequent paragraphs. This contaminant resulted from acid fluxed soldering being conducted in the room. [Pg.168]

Volatilization of selenium from volcanoes, soils, sediments, the oceans, microorganisms, plants, animals, and industrial activity all contribute to selenium in the atmosphere. Natural background concentrations of selenium in nonvolcanic areas are only around 0.01-1 ngm , but the short residence time, usually a matter of weeks, makes the atmosphere a rapid transport route for selenium. Volatilization of selenium into the atmosphere results from microbial methylation of selenium from soil, plant, and water, and is affected by the availability of selenium, the presence of an adequate carbon source, oxygen availability, and temperature (Frankenberger and Benson, 1994 Jacobs, 1989). [Pg.4594]

Carbon dioxide is an important constituent of interest in the field of air pollution, from both local and global perspectives. Its anthropogenic sources include combustion of fossil fuels and depletion of rain forests. The background concentration of carbon dioxide in the northern hemisphere has risen from approximately 310 ppm in the middle of the 20th century to 369 ppm in 2000. This situation is connected to the greenhouse effect and has become an important issue beyond national boundaries. Moreover, enormous amounts of CO are generated by incomplete combustion of carbonaceous fuels such as wood, coal, gasoline, and natural gas. From the human health point of view, the current U.S. Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for CO is 50 ppm. The exposure standard recommended by the... [Pg.244]

Carbon-14 ( " C, half-life = 5730 yr) is also formed cosmogenically by interactions with atmospheric nitrogen. This quickly gets mixed with the stable carbon pool and background concentrations are typically about 227 Bq kg stable carbon. Increasing fossil-fuel emissions, which are depleted in " C are diluting this carbon isotope so that the ratio of " C to is decreasing over time in the atmosphere. [Pg.85]

The concentration of is determined by measurement of the specific P-activity. Usually, the carbon from the sample is converted into a gas, eg, carbon dioxide, methane, or acetylene, and introduced into a gas-proportional counter. Alternatively, Hquid-scintiHation counting is used after a benzene synthesis. The limit of the technique, ca 50,000 yr, is determined largely by the signal to background ratio and counting statistics. [Pg.418]

Under low-dose conditions, forest ecosystems act as sinks for atmospheric pollutants and in some instances as sources. As indicated in Chapter 7, the atmosphere, lithosphere, and oceans are involved in cycling carbon, nitrogen, oxygen, sulfur, and other elements through each subsystem with different time scales. Under low-dose conditions, forest and other biomass systems have been utilizing chemical compounds present in the atmosphere and releasing others to the atmosphere for thousands of years. Industrialization has increased the concentrations of NO2, SO2, and CO2 in the "clean background" atmosphere, and certain types of interactions with forest systems can be defined. [Pg.116]

The information obtained during the background search and from the source inspection will enable selection of the test procedure to be used. The choice will be based on the answers to several questions (1) What are the legal requirements For specific sources there may be only one acceptable method. (2) What range of accuracy is desirable Should the sample be collected by a procedure that is 5% accurate, or should a statistical technique be used on data from eight tests at 10% accuracy Costs of different test methods will certainly be a consideration here. (3) Which sampling and analytical methods are available that will give the required accuracy for the estimated concentration An Orsat gas analyzer with a sensitivity limit of 0.02% would not be chosen to sample carbon monoxide... [Pg.537]

The detection of impurities or surface layers (e.g., oxides) on thick specimens is a special situation. Although the X-ray production and absorption assumptions used for thin specimens apply, the X-ray spectra are complicated by the background and characteristic X rays generated in the thick specimen. Consequently, the absolute detection limits are not as good as those given above for thin specimens. However, the detection limits compare very favorably with other surface analysis techniques, and the results can be quantified easily. To date there has not been any systematic study of the detection limits for elements on surfaces however, representative studies have shown that detectable surface concentrations for carbon and... [Pg.361]


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See also in sourсe #XX -- [ Pg.261 ]




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