Carbon monoxide hydroxyl radical reaction

PCBTF received an exemption from VOC regulations based on the fact that its atmospheric hydroxyl radical reaction rate is slower than that of ethane [25]. A VOC is defined as any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic add, metallic carbides or carbonates, and ammoniiun carbonate, which partidpates in atmospheric photochemical reactions [26]. A VOC exemption petition for BTF was filed with the EPA on March 11,1997. Volatile organic compounds (VOCs) emission is controlled by regulation in efforts to reduce the tropospheric air concentrations of ozone. 

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. 

Reactions 2-6 through 2-8 form a catalytic cycle, in that the hydroxyl radical that is used in Reaction 2-6 is r enerated in Reaction 2-8. The net results of this cycle are the oxidations of nitric oxide to nitrogen dioxide and carbon monoxide to carbon dioxide by the oxygen present in the air. 

A further use of the system is to mediate the reaction of adamantane with carbon monoxide and oxygen to form 1-adamantanecarboxylic acid . When long-wavelength light (>300 nm) is used, hydroperoxides efficiently generate hydroxyl radicals without the use of metal ions and would be an extremely useful source of hydroxyl radicals, particularly in the design of DNA-cleaving molecules . ... 

Important peroxy radical sources include the reactions of the hydroxyl radical with various compounds, for example, carbon monoxide ... 

The methane flame may be used as an example of the present state of knowledge of a flame system. In the reaction zone of this flame, the attack of hydroxyl radical on methane is followed rapidly by the further decomposition of the methyl radical into carbon monoxide and active species. CO is oxidized slowly in an equilibration zone by the reaction... 

As Barr et al. (2003) pointed out, the importance of such emissions is determined mainly by their impact on the three processes taking place in the atmosphere. The first consists in that such NMHCs as isoprene form in the course of carboxylization in plants and contribute much thereby to the formation of biospheric carbon cycle. The second process is connected with NMHCs exhibiting high chemical activity with respect to such main oxidants as hydroxyl radicals (OH), ozone (03), and nitrate radicals (N03). Reactions with the participation of such components result in the formation of radicals of alkylperoxides (R02), which favor efficient transformation of nitrogen monoxide (NO) into nitrogen dioxide (N02), which favors an increase of ozone concentration in the ABL. Finally, NMHC oxidation leads to the formation of such carbonyl compounds as formaldehyde (HCHO), which stimulates the processes of 03 formation. Finally, the oxidation of monoterpenes and sesquiterpenes results in the intensive formation of fine carbon aerosol with a particle diameter of <0.4 pm... 

Carbon Monoxide Oxidation. Analysis of the carbon monoxide oxidation in the boundary layer of a char particle shows the possibility for the existence of multiple steady states (54-58). The importance of these at AFBC conditions is uncertain. From the theory one can also calculate that CO will bum near the surface of a particle for large particles but will react outside the boundary layer for small particles, in qualitative agreement with experimental observations. Quantitative agreement with theory would not be expected, since the theoretical calculations, are based on the use of global kinetics for CO oxidation. Hydroxyl radicals are the principal oxidant for carbon monoxide and it can be shown (73) that their concentration is lowered by radical recombination on surfaces within a fluidized bed. It is therefore expected that the CO oxidation rates in the dense phase of fluidized beds will be suppressed to levels considerably below those in the bubble phase. This expectation is supported by studies of combustion of propane in fluidized beds, where it was observed that ignition and combustion took place primarily in the bubble phase (74). More attention needs to be given to the effect of bed solids on gas phase reactions occuring in fluidized reactors. 

Further reaction of carbon monoxide with hydroxyl radical yields carbon dioxide (equation 8.35), whereas reaction of carbon monoxide with carbine yields ketene (equation 8.36) [14], Atomic hydrogen, in turn, converts carbon monoxide to formaldehyde (equations 8.37-8.38), which in principle may be a substrate for prebiotic... 

In ambient air, the primary removal mechanism for acrolein is predicted to be reaction with photochemically generated hydroxyl radicals (half-life 15-20 hours). Products of this reaction include carbon monoxide, formaldehyde, and glycolaldehyde. In the presence of nitrogen oxides, peroxynitrate and nitric acid are also formed. Small amounts of acrolein may also be removed from the atmosphere in precipitation. Insufficient data are available to predict the fate of acrolein in indoor air. In water, small amounts of acrolein may be removed by volatilization (half-life 23 hours from a model river 1 m deep), aerobic biodegradation, or reversible hydration to 0-hydroxypropionaldehyde, which subsequently biodegrades. Half-lives less than 1-3 days for small amounts of acrolein in surface water have been observed. When highly concentrated amounts of acrolein are released or spilled into water, this compound may polymerize by oxidation or hydration processes. In soil, acrolein is expected to be subject to the same removal processes as in water. 

These NO emissions reduce the steady-state concentration of ozone due to reaction (c). However, cars also emit carbon monoxide and a variety of hydrocarbons (HC) as a result of incomplete combustion. These emissions react with the hydroxyl radical to produce peroxy radicals ... 

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... 

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. 

The reaction of carbon monoxide with hydroxyl radicals is a very important reaction in the lower atmosphere. It oxidizes CO, a highly toxic gas... 

T T ntil recently the role of carbon monoxide in polluted atmospheres has been largely ignored. Heicklen, Westberg, and Cohen (i) suggested that hydroxyl radicals, postulated as intermediates in the reaction... 

Whether or not CO can affect an increase in the oxidation rate of NO in the presence of hydrocarbons depends on the relative rates of these competing reactions. For a highly reactive hydrocarbon such as mesity-lene, the reaction of the hydrocarbon with hydroxyl radicals is so fast that the reaction of CO with OH cannot compete even at high CO-hydrocarbon ratios. For less reactive hydrocarbons such as ethylene and 1-butene, CO competes with the hydrocarbon for the OH radicals and, in systems containing these hydrocarbons, a carbon monoxide effect is possible. The rate constant for the reaction of ethylene with hydroxyl radicals has been measured to be 3.6 X 10 1/mole-sec 15). This is forty times greater than the rate constant of 8.9 X 10 1/mole-sec (JO) for the reaction of OH with CO. Therefore, a CO effect should be possible at CO-ethylene ratios of 40 or greater. Experimentally, an increase in the NO oxidation rate for this system was observed at a CO—hydrocarbon ratio of 50. 

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). 

Carbon monoxide (CO), a toxic gas, is produced during combustion, both in wildfires and in fuel-burning devices CO also can be produced and consumed by bacterial activity. The presence of CO may indirectly increase the atmospheric mixing ratios of other gases by competing for oxidant species (such as the hydroxyl radical, OH-), thereby decreasing the oxidation rates of the other gases. This competition for oxidant species is believed to be one reason for the current increase in atmospheric methane, whose major atmospheric sink is reaction with the hydroxyl radical. 

The most abundant carbon-containing compound in the stratosphere and mesosphere is carbon dioxide (CO2). By interacting with infrared radiation, this gas plays an important role in the thermal budget of the atmosphere, and the 30% increase in its concentration resulting mainly from fossil fuel burning has provided a significant forcing to the climate system of about 1.5 Wm 2 (IPCC, 2001). Carbon dioxide does not play any substantial role in the chemistry of the atmosphere except in the lower thermosphere, where its photolysis is an important source of carbon monoxide (CO). This latter gas, which is also released at the Earth s surface by incomplete combustion (pollution) and is partially transported to the stratosphere, is converted to CO2 by reaction with the hydroxyl radical (OH). 

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