The global balance of carbon monoxide

Abstract

Radioactive carbon-14 monoxide produced by cosmic ray neutrons provides a useful tracer to deduce the residence time of carbon monoxide in the troposphere. From the steady-state equations for stable carbon monoxide and radioactive carbon monoxide, the production rate of stable carbon monoxide can also be derived. This rate is an order of magnitude greater than that estimated for CO sources such as the oceans, combustion, and chlorophyll decay. The oxidation of tropospheric methane initiated by hydroxyl radicals has been postulated to account for this predominant source of CO in nature. Estimates of the steady-state hydroxyl radical concentration in the troposphere are of sufficient magnitude to support this possibility. Furthermore, the hydroxyl radical can also provide the major removal mechanism for carbon monoxide by oxidation to CO, to maintain the carbon monoxide balance in nature. A critical review of the above theories is given, and some possibilities for experimcntal verification are discussed. The earlier computations are modified to refer to the northern troposphere in view of differences recently found for CO concentrations in the northern and southern troposphere. Observations of the stable isotope composition of methane, W H , and WH,, and of carbon monoxide, 12CI6O, 13C160, and lZClsO are also of significance to the proposed theory for the carbon monoxide balance. These data will be raviewed and discussed in terms of kinetic isotope effects in the reaction sequence, CH, to CO to CO,. The results of this analysis of the stable CO isotope data will be shown to be consistent with the conclusions drawn from the analysis of the radiocarbon data.

Mechanisms and observations for isotope fractionation of molecular species in planetary atmospheres

“…This is less depleted in •3CH,, than most of the expected sources of atmospheric CH½ [Stevens and Rust, 1982' Tyler, 1986]. Similar calculations, using older values of {5•3C for CH½[Ehhalt, 1973], have been presented previously byWeinstock and Chang [1974].No data are available on the •3C isotope effect on the less important C1 + CH½ reaction, however, although the similarity in reaction rates (especially activation energies) between the OH and C1 reactions suggests that they could be expectedto have similar isotope effects. The O(•D) reaction appears to have little or no isotope effect' Davidson et al [1987] measured a ratio of rates of the reaction at room temperature involving •2CH,, and •3CH,, of 1.001.…”

“…The breakdown of sources helps one to understand the annual variation in 5x3C explained in the previous paragraph. Weinstock and Chang [1974] attempted to reconcile the 5X3C measurements for CH,• and CO by noting that the isotope effect for the CO destruction reaction (reaction (59)) is related to that of the CH,• destruction reaction (reaction (57)…”

Global air pollution and climatic change

“…Table 4 summarizes the various CO2 emission estimates from anthropogenic and natural global sources [SCEP, 1970;Lovelock, 1971;Hidy, 1973;Williamson, 1973]. It must be pointed out that the CO• emission estimates in Table 4 [1973], respectively, would result in residence times of 16-18 yr and not in residence times of 2-5 yr, which is given by these authors (Table 7) to 1600 Mt/yr [Robinson and Moser, 1971] to 1814 Mt/yr [Lovelock, 1971] to 2086 Mt/yr [Weinstock and Chang, 1974]. Methane is produced by a group of anaerobic bacteria which exist in anoxic environments rich in organic matter [Wolfe, 1971].…”

“…Levy [1971 ],McConnell et al [1971 ],Weinstock and Chang [1974], Crutzen[1974], and, showing the removal mechanism of these substances in the troposphere. needed in (13) is eventually regenerated by the reaction shown in (8).…”