Carbon monoxide lifetime

On the basis of ratios of C and C present in carbon dioxide, Weinstock (250) estimated a carbon monoxide lifetime of 0.1 year. This was more than an order of magnitude less than previous estimates of Bates and Witherspoon (12) and Robinson and Robbins (214), which were based on calculations of the anthropogenic source of carbon monoxide. Weinstock (250) suggested that if a sufficient concentration of hydroxyl radical were available, the oxidation of carbon monoxide by hydroxyl radical, first proposed by Bates and Witherspoon (12) for the stratosphere, would provide the rapid loss mechanism for carbon monoxide that appeared necessary. By extension of previous stratospheric models of Hunt (104), Leovy (150), Nicolet (180), and others, Levy (152) demonstrated that a large source of hydroxyl radical, the oxidation of water by metastable atomic oxygen, which was itself produced by the photolysis of ozone, existed in the troposphere and that a chain reaction involving the hydroxyl and hydroperoxyl radicals would rapidly oxidize both carbon monoxide and methane. It was then pointed out that all the loss paths for the formaldehyde produced in the methane oxidation led to the production of carbon monoxide [McConnell, McElroy, and Wofsy (171) and Levy (153)1-Similar chain mechanisms were shown to provide tropospheric... 

Fenner (11) has pointed out that short-lifetime constituents of the atmosphere such as nitrogen oxides, carbon monoxide, and nonmethane hydrocarbons may also play roles related to global warming because of their chemical relations to the longer-lived greenhouse gases. Also, SO, with a very short life interacts with ozone and other constituents to be converted to particulate sulfate, which has effects on cloud droplet formation. 

Thirdly, trapping of highly unstable carbonium ions, such as primary alkyl and vinyl ions, by carbon monoxide has been shown possible, so that their existence as distinct species with a finite lifetime has gained in plausibility. 

Reaction 2-6 is sufficiently fast to be important in the atmosphere. For a carbon monoxide concentration of 5 ppm, the average lifetime of a hydroxyl radical is about 0.01 s (see Reaction 2-6 other reactions may decrease the lifetime even further). Reaction 2-7 is a three-body recombination and is known to be fast at atmospheric pressures. The rate constant for Reaction 2-8 is not well established, although several experimental studies support its occurrence. On the basis of the most recently reported value for the rate constant of Reaction 2-8, which is an indirect determination, the average lifetime of a hydroperoxy radical is about 2 s for a nitric oxide concentration of 0.05 ppm. Reaction 2-8 is the pivotal reaction for this cycle, and it deserves more direct experimental study. 

Two final examples of the sensitivity and general applicability of the FTIR gas analysis technique are illustrated in Fig. 8. Trace (A) shows the spectrum obtained from an ultra-air filled 70 liter sampling bag into which had been injected, 18 hours previously, 4.8 microliters of TDI, toluene diisocyanate. On the basis of the single feature at 2273 cm l, it is estimated that 50 ppb TDI could be detected. The lower Trace (B), shows the spectrum of nickel carbonyl. This highly toxic but unstable gas was found to decay rapidly at ppm concentrations in ultra air (50% lifetime 15 minutes). Calibration of its spectrum was established by recording successive spectra at ten minute intervals and by attributing the increase in carbon monoxide concentration (calibration known) to an equivalent but four times slower decrease in nickel carbonyl concentration. The spectrum shown represents 0.6 ppm of the material. Note the extraordinary absorption strength. The detection limit is thus less than 10 ppb. 

Since C has been assigned to a triplet deoxy state in which the axial ligand has been dissociated. As can be seen in Table 111, in most cases lifetimes are found to compare favorably between the carbon monoxide and oxygen forms of the synthetic complexes. In all cases the rate constants used had an accuracy of only one significant figure, resulting in an accuracy no better for the lifetimes or these states. One noticeable discrepancy in occurs between the chelated protoheme 1 -CO and the oxygen form of this compound, i 02. 

The photolysis of trifluoroacetone with light of wavelength 3130 A. has been studied by Sieger and Calvert.48 The products of decomposition were shown to be carbon monoxide, methane, ethane, 1,1,1-trifluoro-ethane, and hexafluoroethane. There was no indication of the presence of carbon tetrafluoride or methyl fluoride. The quantum yield of all products was low at low temperature and it is assumed that the excited molecule of trifluoroacetone has an appreciable lifetime and may be deactivated by collision before decomposition can occur. This contention is supported by the decrease in the quantum yields observed when foreign gases such as carbon dioxide are added, and by the fall in quantum yields with increase in trifluoroacetone concentration. 

The quantum yield of carbon monoxide was of the order of 0.8 and did not vary greatly over the range of pressure studied, suggesting that the excited molecule of the halogenated acetone had only a comparatively short lifetime. This behavior is in contrast with that reported for hexafluoroacetone. A further indication that the carbon monoxide arises by a reaction of type B is given by the fact that the intensity exponent is almost exactly unity. 

The reaction of 02 with cytochrome c oxidase to form the oxygenated species A (Fig. 18-11) is very rapid, occurring with apparent lifetime T (Eq. 9-5) of -8-10 is.139 Study of such rapid reactions has depended upon a flow-flash technique developed by Greenwood and Gibson.136/140/141 Fully reduced cytochrome oxidase is allowed to react with carbon monoxide, which binds to the iron in cytochrome a3 just as does 02. In fact, it was the spectroscopic observation that only half of the... 

Coordinatively labile ruthenium(II) porphyrins Ru(P)(THF)2 (P = TTP, TMP) catalyse the cis- trans isomerization of epoxides under mild conditions, probably by coordination of the epoxide and ring opening via a carbon radical [365]. The lifetime of the catalysts is restricted due to carbon monoxide abstraction from coordinated epoxide to yield inactive carbonylruthenium(II) complexes, e.g. RuCO(TMP)THF [366],... 

Zewail and his co-workers addressed this question in their laboratory and studied the stability of the tetramethylene diradical generated from various precursors in real time. He showed with femtosecond spectroscopy that intermediate product was in fact formed and had a lifetime of 700 fs. Using cyclopentanone as the precursor they have shown that with two photons at 310 nm (pump) carbon monoxide is eliminated through an a-cleavage. 

The colorless carbon monoxide (CO) is everywhere. Wherever there is combustion there is CO it is the predominant product above 800°C. The concentration of CO might vary from 0.1 ppm in clean atmosphere to 5,000 ppm in the proximity of domestic wood fire chimneys (Fawcett et al, 1992) and is present in significant quantities in cigarette smoke (Hartridge, 1920 Hoffman et al, 2001). The atmospheric lifetime of CO is 1 to 2 months, which allows its intercontinental transport (Akimoto, 2003). 

Carbon monoxide is not a greenhouse gas, but its chemical effects on the OH radical alfect the destruction of CH4 and the formation of ozone. Because the concentration of CO is low and its lifetime is short, its atmospheric budget is less well understood than budgets for CO2 and CH4. Nevertheless, CO seems to have been increasing in the atmosphere until the late 1980s (Prather and Ehhalt, 2001). Its contribution to the carbon cycle is very small. 

Sieger and Calvert reported the photolysis products of 1,1,1-trifluoroacetone at A 3130 A to be carbon monoxide, methane, ethane, 1,1,1-trifluoroethane, and hexafluoroethane. A low quantum yield for decomposition near room temperature may be explained in terms of the excited trifluoroacetone having an appreciable lifetime and therefore suffering possible collisional deactivation before decomposition can occur. Two possible primary stepts of Type 1 have been proposed... 

A particularly important application of nanoscale catalysis is the oxidation of atmospheric pollutants such as carbon monoxide to less harmful products [47-49]. One challenge has been to find a suitable catalytic material with a sufficient active lifetime to induce the oxidation of CO. Recent findings by Harata and cowoikers danonstrated that nanosized gold particles deposited onto selected metal oxides exhibited high activities for the low-tanperature oxidation of carbon monoxide [9-12]. These studies also established... 

Transition metal catalysts, specifically those composed of iron nanoparticles, are widely employed in industrial chemical production and pollution abatement applications [67], Iron also plays a cracial role in many important biological processes. Iron oxides are economical alternatives to more costly catalysts and show activity for the oxidation of methane [68], conversion of carbon monoxide to carbon dioxide [58], and the transformation of various hydrocarbons [69,70]. In addition, iron oxides have good catalytic lifetimes and are resistant to high concentrations of moisture and CO which often poison other catalysts [71]. Li et al. have observed that nanosized iron oxides are highly active for CO oxidation at low tanperatures [58]. Iron is unique and more active than other catalyst and support materials because it is easily reduced and provides a large number of potential active sites because of its highly disordered and defect rich structure [72, 73]. Previous gas-phase smdies of cationic iron clusters have included determination of the thermochemistry and bond energies of iron cluster oxides and iron carbonyl complexes by Armentrout and co-workers [74, 75], and a classification of the dissociation patterns of small iron oxide cluster cations by Schwarz et al. [76]. 

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