Oxides of nitrogen and hydrocarbons

Heikes, B M. Lee, D. Jacob, R. Talbot, J. Bradshaw, H. Singh, D. Blake, B. Anderson, H. Fuelberg, and A. M. Thompson, Ozone, Hydroperoxides, Oxides of Nitrogen, and Hydrocarbon Budgets in the Marine Boundary Layer over the South Atlantic, J. Geophys. Res., 101, 24221-24234 (1996). 

In the following sections we shall look at the major ingredients of photochemical smog—the oxides of nitrogen and hydrocarbons, and the secondary pollutant ozone. 

Photochemical oxidants n. Secondary pollutants formed by the action of sunlight on the oxides of nitrogen and hydrocarbons in the air. They are the primary contributors to photochemical smog. 

Chemistry of Oxides of Nitrogen and Hydrocarbons. The chemistry of the polluted atmosphere is exceedingly complex. Several hundred chemical reactions are known to occur in a mixture of only a single hydrocarbon, oxides of nitrogen, carbon monoxide, water vapor, and air. The polluted atmosphere contains hundreds of different hydrocarbons, each with its own reactivity and reaction products. The classes of major primary pollutants in the polluted atmosphere are given in Table I. In this section we focus on the chemistry of the oxides of nitrogen and hydrocarbons. 

Annual trends in urban ozone are much more subtle because of the complex interaction among precursors (hydrocarbons and oxides of nitrogen) and meteorology (including solar radiation) (Fig. 4-5). 

It is not feasible to model the reaction of each hydrocarbon species with oxides of nitrogen. Therefore, hydrocarbon species with similar reactivities are lumped together, e.g., into four groups of reactive hydrocarbons olefins, paraffins, aldehydes, and aromatics (32). 

The increasing number of atomic reactors used for power generation has been questioned from several environmental points of view. A modern atomic plant, as shown in Fig. 28-3, appears to be relatively pollution free compared to the more familiar fossil fuel-fired plant, which emits carbon monoxide and carbon dioxide, oxides of nitrogen and sulfur, hydrocarbons, and fly ash. However, waste and spent-fuel disposal problems may offset the apparent advantages. These problems (along with steam generator leaks) caused the plant shown in Fig. 28-3 to close permanently in 199T. 

Absorption of pollutant gases is accomplished by using a selective liquid in a wet scrubber, packed tower, or bubble tower. Pollutant gases commonly controlled by absorption include sulfur dioxide, hydrogen sulfide, hydrogen chloride, chlorine, ammonia, oxides of nitrogen, and low-boiling hydrocarbons. 

Combustion processes are the most important source of air pollutants. Normal products of complete combustion of fossil fuel, e.g. coal, oil or natural gas, are carbon dioxide, water vapour and nitrogen. However, traces of sulphur and incomplete combustion result in emissions of carbon monoxide, sulphur oxides, oxides of nitrogen, unburned hydrocarbons and particulates. These are primary pollutants . Some may take part in reactions in the atmosphere producing secondary pollutants , e.g. photochemical smogs and acid mists. Escaping gas, or vapour, may... 

In April of 1998, the EPA published a final rule for emission of oxides of nitrogen (NOx), hydrocarbons (EIC), carbon monoxide (CO), particulate matter (PM), and smoke opacity for newly manufactured and rcmanufacturcd locomotives. The rulemaking took effect in 2000 and is estimated by the EPA to cost the railroads 80 million per year—about 163 per ton of NOx reduced, according to EPA figures. The emissions standards for the several pollutants will be implemented in three tiers—for locomotives... 

Indeed, in developing complete mechanisms for the oxidation of CO and hydrocarbons applicable to practical systems over a wide range of temperatures and high pressures, it is important to examine the effect of the H02 reactions when the ratio is as high as 10 or as low as 0.1. Considering that for air combustion the total concentration (M) can be that of nitrogen, the boundaries of this ratio are depicted in Fig. 3.3, as derived from the data in Appendix C. These modem rate data indicate that the second explosion limit, as determined... 

Schuck, E. A., and G. J. Doyle. Photooxidation of Hydrocarbons in Mixtures Containing Oxides of Nitrogen and Sulfor Dioxide. Report No. 29. San Marino, Calif. Air Pollution Foundation, 1959. 126 pp. 

TPO analyses were performed in a TPD/TPR 2900 (Micromeritics) equipment with a thermal conductivity detector a trap for sulfur compounds and a Pt/Silica bed for oxidation of CO and hydrocarbons to CO2. Eurthermore, it has a cold trap (isopropyl alcohol/liquid nitrogen) to condense CO2 and residual moisture. The combustion products are passed through the previous traps connected in series in order to remove other compounds different from O2 in the carrier gas. This ensures that the conductivity changes observed in the detector are attributed exclusively to changes in oxygen concentration in the carrier gas. 

Complex oxides of the perovskite structure containing rare earths like lanthanum have proved effective for oxidation of CO and hydrocarbons and for the decomposition of nitrogen oxides. These catalysts are cheaper alternatives than noble metals like platinum and rhodium which are used in automotive catalytic converters. The most effective catalysts are systems of the type Lai vSrvM03, where M = cobalt, manganese, iron, chromium, copper. Further, perovskites used as active phases in catalytic converters have to be stabilized on the rare earth containing washcoat layers. This then leads to an increase in rare earth content of a catalytic converter unit by factors up to ten compared to the three way catalyst. 

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