current research Carbon Monoxide in Lower Atmosphere Reactions Basil Dimitriades a n d Marvin Whisman Bartlesville Petroleum Research Center, Bureau of Mines, U.S. Department of the Interior, Bartlesville, Okla. 74003
To understand more fully pollution problems posed by carbon monoxide, an experimental study of CO reactions in the lower atmosphere was conducted. The study involved exposure of CO to lower atmospheric conditions simulated in the laboratory and measurement of rate of CO oxidation into C o r . To simplify analytical measurements, the CO reactant was mixed with CI4-labeled CO. Results suggested that the C O oxidation rate in the lower atmosphere is approximately 0.05% per hour of day- or night-time, resulting in a lifetime of 0.3 year; observed rates cannot be explained only by CO reactions with oxygen atoms and ozone; and the presence of CO at typical levels does not necessarily af'fect the process of photochemical smog formation.
Rate of C1402 formation was measured and was taken t o represent rate of CO oxidation. Reactant mixtures in the initial reactor charge were designed t o contain various levels of hydrocarbons, nitric oxide, nitrogen dioxide, carbon monoxide, and carbon dioxide in purified air. Hydrocarbons and nitrogen oxides were used to provide reaction systems similar to those encountered in polluted lower atmospheres. Such reaction systems are characterized by the presence of reactive species, such as oxygen atoms, radicals, and peroxy-type compounds. Carbon monoxide was the reactant of direct interest and was used in mixture with C14-labeled CO. Carbon dioxide was used at varying levels because it has been suggested that COn may affect oxidation of CO by oxidizing species such as ozone (Harteck and Dondes, 1957). In general, two types of reactant mixtures were used: synthetic mixtures of 1-butene NO2 CO, and automotive exhaust mixtures with their normal content of NO, NOi, CO, COS, and HnO, plus added varying amounts of Cl4-labeled CO. Table I summarizes exact reactant mixture compositions. The test procedure involved irradiation of the reactant mixture with artificial sunlight under conditions approximating those in a typical urban atmosphere. The irradiation vessel (Figure 1) was a 50-liter borosilicate-glass flask equipped with a magnetic Teflon stirrer and an all-glass pumping system for recirculating gaseous contents of the reactor through a sampling port. Irradiation was provided by a n array of sunlamps, bluelamps, and blacklight fluorescent lamps (12 in all) surrounding the spherical reactor. Light intensity in terms of the NOz photolysis constant (Tuesday, 1961), Kd, was 0.17 min-'. Reactor temperature was controlled with use of infrared lamps for heating and circulation of room air through the space between lamps and reactor walls for cooling. During a test the reactor temperature was 25OC 1 '. The reactor was charged by injecting measured volumes of either synthetic blends or exhaust + NS(1 to 6) mixtures that had been collected in a Tedlar bag (Fleming et ul., 1965). For measurement of rate of CO oxidation, the reactants were irradiated for 4 or 5 h r and the reaction mixture was analyzed every 30 min or 1 h r for C14O and C140z.Total radioactivity was also measured periodically t o ensure absence of, or calculate effects from, interfering processes such as dilution of reactor content and loss of C14-labeled material on reactor walls or sampling equipment. To measure CO and COS, the two carbon oxides were first separated chromatographically from reaction mixture and from each other; then CO was converted into COz with a microcombustor; finally, COSproduced from either C O combustion or the chromatographic separation of reaction mixture was
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he origin and fate of CO in the earth's atmosphere were studied primarily because, by virtue of its abundance and toxicity, CO has become a n increasingly hazardous atmospheric pollutant. Although as a result of fossil-fuel combustion the problem is presently localized in urban areas only, atmospheric CO observations have been sufficiently extensive to establish appearance-disappearance patterns on a globewide basis. One finding, established by such observations, is that the annual C O buildup in the earth's atmosphere is far less than the amount of CO that is known to be discharged annually t o the atmosphere (Jaffe, 1968). This suggests the presence of a n unidentified process that results in CO removal. This process must be defined before the magnitude of the pollution problem posed by CO can be fully understood. The work reported here constitutes a part of an effort concerned with the formation and consumption of C O in photochemical reaction systems similar to those encountered in the lower atmosphere. Experimental evidence obtained from this effort was used to establish the extent t o which chemical reactions in the polluted lower atmosphere constitute a process by which CO is removed from the atmosphere through conversion into COS. The possibility that C O participates in lower atmosphere reactions is interesting also from the standpoint of understanding the reactions responsible for photochemical smog formation. Experirnental
The experimental program consisted of tests in which C14-labeled CO was exposed to reaction mixtures and conditions typically prevailing in polluted lower atmospheres.
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Volume 5, Number 3, March 1971 219
Table I.
Composition of Initial Reactant and Rate of CO Oxidation in Photoirradiated Hydrocarbon-Noxa-CO-Air Mixtures
Initial charge Sample type Pure air Pure air Pure air Pure air 1-Butene 1-Butene 1-Butene 1-Butene 1-Butene Exhaust Exhaust Exhaust Exhaust Exhaust
Hydrocarbon, NO NO, cob c140 cot* ~ 1 4 0 PPm ppmc
