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A review is given of the use of radiocarbon as a direct measure of the relative importance of natural and anthropogenic sources of carbonaceous gases and particles. Through the use of a specially designed, low-level gas proportional counting system, the biospheric (living) carbon fraction has been determined in selected chemical species containing as little as 5 mg of carbon. The species of interest include those that are climatically active and those that have an impact on air quality, such as methane, carbon monoxide, nonmethane hydrocarbons, and carbonaceous particles.
Major factors considered in the interpretation of the radiocarbon data include the chemical and isotopic composition of carbonaceous sources, and natural and man-induced perturbations of biospheric radiocarbon. In order to ensure reliable conclusions, therefore, we have incorporated chemical and size selectivity and data on the recent history of radiocarbon fluctuations. Exploratory studies on selected urban and rural aerosol samples have thus far reflected the dominance of man's activities for the urban locales. This has been seen in the large fossil carbon content of particles from cities having only natural biospheric sources, and in the large biospheric carbon content of urban (Portland, Ore.) particles collected during periods of wood and grass burning.
Measurement advances, including the development of multiple counter systems and accelerator mass spectrometry, promise increased utilization of natural radiocarbon as an environmental tracer, in addition to its application to the rarer atmospheric components.
atmospheric gases, atmospheric particles, carbonaceous pollutants, anthropogenic pollutant sources, natural pollutant sources, environmental radiocarbon, climatically active species, low-level counting, accelerator mass spectrometry, organics, toxic organics, atmosphere, radiocarbon fluctuations
Research scientist, Gas and Particulate Science Division, Center for Analytical Chemistry, National Bureau of Standards, Washington, D.C.,