Carbon monoxide from automotive emissions

Advances in personal monitoring for exposure assessment studies are currently dependent upon the development of reliable analytical techniques and instrumentation applicable to PEMs. Currently PEMs for carbon monoxide are the most highly developed and evaluated. Carbon monoxide is an emission product which can be directly related to lead emissions from automotive combustion. Personal exposure monitors for CO are being used in urban studies to obtain population exposure data on a real time basis. This information can be used in risk assessment. 

In fact, most of us benefit from the use of catalysis. Automotive catalytic converters have represented the most massive application of environmental catalysis and one of the most challenging and successful cases in catalysis, generally. Automobile catalysts deseive a few more comments. The engine exhaust emission is a complex mixture, whose composition and flow rate change continuously depending on a variety of factors such as driving conditions, acceleration, and speed. Despite the variability of the conditions, three-way catalysts have achieved the reduction of exhaust carbon monoxide, hydrocarbons, and... 

As mentioned earlier, the oxidation of carbon monoxide and hydrocarbons should be achieved simultaneously with the reduction of nitrogen oxides. However, the first reaction needs oxygen in excess, whereas the second one needs a mixture (fuel-oxygen) rich in fuel. The solution was found with the development of an oxygen sensor placed at exhaust emissions, which would set the air-to-fuel ratio at the desired value in real time. So, the combination of electronics and catalysis and the progress in these fields led to better control of the exhaust emissions from automotive vehicles. 

Another important application of heterogeneous catalysts is in automobile catalytic converters. Despite much work on engine design and fuel composition, automotive exhaust emissions contain air pollutants such as unburned hydrocarbons (CxHy), carbon monoxide, and nitric oxide. Carbon monoxide results from incomplete combustion of hydrocarbon fuels, and nitric oxide is produced when atmospheric nitrogen and oxygen combine at the high temperatures present in an... 

Carbon monoxide emissions from internal combustion engines are commonly plotted as functions of air/fuel ratio or fuel/air ratio. Fuel/air ratio is merely the reciprocal of air/fuel ratio.34 It has generally been accepted by the automotive experts that the CO level of Diesel exhaust is related chiefly to these ratios and not to other factors, such as rpm. 

The chemical and thermal characteristics of PGE make them highly useful as catalysts in a wide variety of industrial, chemical, electrical and pharmaceutical processes (Johnson Matthey 2007). Their use as catalysts in automotive catalytic converters to reduce noxious emissions from the burning of fossil fuels has undoubtedly been one of the most far-reaching and important applications. Automobiles have been equipped with catalytic converters since 1975 and 1986 in the US and Europe, respectively. Initially, Pt and Pd were used to reduce hydrocarbon and carbon monoxide emissions. Since the early 1990s, Rh has also been used in various combinations and ratios with Pt and Pd in three-way catalytic converters to reduce emissions. PGE appear to be emitted together with alumina particles from the washcoat as a result of various chemical, physical and... 

In the United States, The Clean Air Act of 1970 mandated the reduction of automotive pollutant emissions. The most effective way to accomplish the reduction of emissions was through the use of a catalytic converter. It s shaped like a muffler and connected to the exhaust system of an automobile. It has a solid catalyst, either palladium or platinum, inside. When the exhaust gases pass over the catalyst, the catalytic converter helps to complete the oxidation of the hydrocarbons and carbon monoxide to carbon dioxide and water. In other words, it helps to change the harmful gases from gasoline to mostly harmless products. 

Automotive equipment emits many chemical species which directly or indirectly can impact on air quality. These emissions are directly evaporated from the fiiel as it is loaded onto a vehicle, as it experiences diurnal temperature cycles in the fuel tank of the vehicle, and as it is heated due to operation of the vehicle. Other emissions enter the atmosphere via the tailpipe after the fuel has been combusted in the engine. These latter emissions may be further modified by passing them over a catalytic converter which is specifically designed to oxidize unburned hydrocarbons and carbon monoxide and to reduce nitrogen oxides. 

The three types of emissions from automotive sources that are of primary concern are unburned hydrocarbons (from either evaporation or the tailpipe), carbon monoxide (CO) and nitrogen oxides (NOx). The latter two are tailpipe emissions only. Most hydrocarbons and NOx are not of concern directly, but they do react with oxygen in the atmosphere under intense sunlight to form ozone, the basic ingredient of urban smog. CO is, of course, directly harmful to human health and is of direct concern. 

Automotives are responsible for about fifty per cent of the total emission of carbon monoxide, unburnt hydrocarbons and nitrogen oxides (see Figure 1.1) which are the origin of many health and environmental problems (Chiron (1987), Impens (1987)). Although emission standards are different from country to country, they are going to become in the near future more and more restrictive. Since an economical clean engine is not available, the catalytic converter is the only practical solution. This is the reason why a lot of research efforts have been directed to the design and optimization of this reactor. 

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