Carbon monoxide, tropospheric

Air pollution (qv) problems are characteri2ed by their scale and the types of pollutants involved. Pollutants are classified as being either primary, that is emitted direcdy, or secondary, ie, formed in the atmosphere through chemical or physical processes. Examples of primary pollutants are carbon monoxide [630-08-0] (qv), CO, lead [7439-92-1] (qv), Pb, chlorofluorocarbons, and many toxic compounds. Notable secondary pollutants include o2one [10028-15-6] (qv), O, which is formed in the troposphere by reactions of nitrogen oxides (NO ) and reactive organic gases (ROG), and sulfuric and nitric acids. 

Photolysis of an aqueous solution containing chloroform (314 pmol) and the catalyst [Pt(cohoid)/Ru(bpy) /MV/EDTA] yielded the following products after 15 h (mol detected) chloride ions (852), methane (265), ethylene (0.05), ethane (0.52), and unreacted chloroform (10.5) (Tan and Wang, 1987). In the troposphere, photolysis of chloroform via OH radicals may yield formyl chloride, carbon monoxide, hydrogen chloride, and phosgene as the principal products (Spence et al., 1976). Phosgene is hydrolyzed readily to hydrogen chloride and carbon dioxide (Morrison and Boyd, 1971). 

Tuazon et al. (1984a) investigated the atmospheric reactions of TV-nitrosodimethylamine and dimethylnitramine in an environmental chamber utilizing in situ long-path Fourier transform infared spectroscopy. They irradiated an ozone-rich atmosphere containing A-nitrosodimethyl-amine. Photolysis products identified include dimethylnitramine, nitromethane, formaldehyde, carbon monoxide, nitrogen dioxide, nitrogen pentoxide, and nitric acid. The rate constants for the reaction of fV-nitrosodimethylamine with OH radicals and ozone relative to methyl ether were 3.0 X 10 and <1 x 10 ° cmVmolecule-sec, respectively. The estimated atmospheric half-life of A-nitrosodimethylamine in the troposphere is approximately 5 min. 

Photolytic. Irradiation of vinyl chloride in the presence of nitrogen dioxide for 160 min produced formic acid, HCl, carbon monoxide, formaldehyde, ozone, and trace amounts of formyl chloride and nitric acid. In the presence of ozone, however, vinyl chloride photooxidized to carbon monoxide, formaldehyde, formic acid, and small amounts of HCl (Gay et al, 1976). Reported photooxidation products in the troposphere include hydrogen chloride and/or formyl chloride (U.S. EPA, 1985). In the presence of moisture, formyl chloride will decompose to carbon monoxide and HCl (Morrison and Boyd, 1971). Vinyl chloride reacts rapidly with OH radicals in the atmosphere. Based on a reaction rate of 6.6 x lO" cmVmolecule-sec, the estimated half-life for this reaction at 299 K is 1.5 d (Perry et al., 1977). Vinyl chloride reacts also with ozone and NO3 in the gas-phase. Sanhueza et al. (1976) reported a rate constant of 6.5 x 10 cmVmolecule-sec for the reaction with OH radicals in air at 295 K. Atkinson et al. (1988) reported a rate constant of 4.45 X 10cmVmolecule-sec for the reaction with NO3 radicals in air at 298 K. 

The evolution of the emissions of some atmospheric pollutants in Europe (EU-15) in the period 1990-1999 has been presented in the report of Goodwin and Mareckova (2002). The report includes acidifying pollutants (ammonia, sulfur dioxide, and nitrogen oxides), tropospheric ozone precursors, NMVOCs, carbon monoxide, and particulate matter... 

Carbon Monoxide. Methods for determining carbon monoxide include detection by conversion to mercury vapor, gas filter correlation spectrometry, TDLAS, and grab sampling followed by gas chromatograph (GC) analysis. The quantitative liberation of mercury vapor from mercury oxide by CO has been used to measure CO (73). The mercury vapor concentration is then measured by flameless atomic absorption spectrometry. A detection limit of 0.1 ppbv was reported for a 30-s response time. Accuracy was reported to be 3% at tropospheric mixing ratios. A commercial instrument providing similar performance is available. 

Reactions R1 - RIO are also key reactions in determining OH distribution in the troposphere and lower stratosphere. The key point here is that increases in ozone and nitrogen oxides enhances the OH distribution through reactions R1 and RIO, while enhanced carbon monoxide and methane reduces OH through reactions R4 and R6. Furthermore, reactions with OH (R4 and R6) represent the main loss of CO and methane. 

In the next few years a number of important atmospheric remote sensing missions are planned by NASDA, NASA and ESA. NASDA has constructed a second ADEOS satellite which will have POLDER and ILAS-II (Improved Limb Atmospheric Sounder) on board. The NASA-TERRA platform was launched at the end of 1999 and has the MOPITT instrument (Measurement of Pollution in the Troposphere), which aims to measure vertical profiles of carbon monoxide and methane in the troposphere. MOPITT is a Canadian instrument supported by an international science team. 

Reichle Jr H.G, V.S. Connors, J.A. Holland, W.D. Hypes, HA. Wallio, J.C. Casas, B.B. Gormsen, M.S. Saylor and W.D. Hesketh (1986) Middle and upper tropospheric carbon monoxide mixing ratios as measured by a satellite-bome remote sensor during November 1981. Journal of Geophysical Research 91 10865-10887... 

Reichle Jr., H.G., V.S. Counors, J.A. Holland, R.T. Sherrill, H.A. Wallio, J.C. Casas, E.P. Condon, B.B. Gormsen and W. Seiler (1990) The distribution of middle tropospheric carbon monoxide during early October 1984. Journal of Geophysical Research 95 9845 9856. 

Conversely, generating hydrogen from sustainable sources would reduce emissions of carbon monoxide and NOx, with a consequent fall in tropospheric ozone levels. This would improve air quality in many regions of the world. Furthermore, C02 emissions would be reduced, thereby slowing the global warming trend. 

The temperature and density structure of the troposphere, along with the concentrations of major constituents, are well documented and altitude profiles have been measured over a wide range of seasons and latitudes for the minor species water, carbon dioxide, and ozone. A few profiles are available for carbon monoxide, nitrous oxide, methane, and molecular hydrogen, while only surface or low-altitude measurements have been made for nitric oxide, nitrogen dioxide, ammonia, sulfur dioxide, hydrogen sulfide, and nonmethane hydrocarbons. No direct measurements of nitric acid and formaldehyde are available, though indirect information does exist. The concentrations of a number of other important species, such as peroxides and oxy and peroxy radicals, have never been determined. Therefore, while considerable information concerning trace constituent concentrations is available, the picture is far from complete. 

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... 

There are over 70 alcohols in the atmosphere as a result of biogenic and anthropogenic emissions [67]. For example methanol and ethanol [68-70] have been used as fuels additives to reduce automobile emissions of carbon monoxide and hydrocarbons [71], in particular ethanol has been used in Brazil as a fuel for over 20 years [72]. 1-Propanol is widely used as a solvent in the manufacturing of different electronic components. The high volatility of these compounds causes their relative abundance in the troposphere and makes it relevant to determine their degradation pathways. During daytime the major loss process for alcohols is their reaction with OH radicals [68]. Accordingly, several experimental [69,70,73-84] and theoretical [85-88] kinetic studies of alcohols -F OH reactions have been performed. 

Carbon monoxide is oxidized in the troposphere ((133) and (134)). With a high concentration of nitric oxide in the troposphere, reactions (135) and (136) take place. This sequence is a formation of ozone catalyzed by nitric oxide. If the nitric oxide concentration is too low, the perhydryl radicals decompose ozone to form hydroxyl radicals (136). Ozone and peroxyacylnitrates PAN are the major toxins of smog. Peroxyacylnitrates are formed from aldehydes in a reaction catalyzed by nitric oxide. 

The hydroxyl radical so produced is the major oxidising species in the troposphere, and a complete picture of its chemistry holds the key to furthering progress in understanding tropospheric chemistry. The chemistry discussed in detail elsewhere, is of course very complex. To take, for example, the cycle of reactions with carbon monoxide, which may be net producers or destroyers of tropospheric ozone depending upon the concentration of oxides of nitrogen present. In the presence of NO, the cycle (16)-(20) occurs, without loss of OH or NO, whereas at low NO concentrations, the cycle (17), (18) and (21), again without loss of OH. 

In fact, evidence gathered by Seiler and Fishman (1981), appears to support the hypothesis that ozone can be produced photochemicaUy in the remote troposphere. They found, for instance, that in several cases measurements in the free troposphere (the region above 1 km) show concentrations of ozone that are correlated positively with levels of carbon monoxide, a photochemical precursor of ozone. 

Sawa Y., Matsueda H., Tsutsumi Y., Jensen J. B., Inoue H. Y., and Makino Y. (1999) Tropospheric carbon monoxide and hydrogen measurements over Kalimantan in Indonesia and northern Australia during October, 1997. Geophys. Res. Lett. 26, 1389-1392. 

Methane is oxidized primarily in the troposphere by reactions involving the hydroxyl radical (OH). Methane is the most abundant hydrocarbon species in the atmosphere, and its oxidation affects atmospheric levels of other important reactive species, including formaldehyde (CH2O), carbon monoxide (CO), and ozone (O3) (Wuebbles and Hayhoe, 2002). The chemistry of these reactions is well known, and the rate of atmospheric CH4 oxidation can be calculated from the temperature and concentrations of the reactants, primarily CH4 and OH (Prinn et al., 1987). Tropospheric OH concentrations are difficult to measure directly, but they are reasonably well constrained by observations of other reactive trace gases (Thompson, 1992 Martinerie et al., 1995 Prinn et al., 1995 Prinn et al., 2001). Thus, rates of tropospheric CH4 oxidation can be estimated from knowledge of atmospheric CH4 concentrations. And because tropospheric oxidation is the primary process by which CH4 is removed from the atmosphere, the estimated rate of CH4 oxidation provides a basis for approximating the total rate of supply of CH4 to the atmosphere from aU sources at steady state (see Section 8.09.2.2) (Cicerone and Oremland, 1988). 

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