Nitrogen oxides and photochemical smog

The majority of nitrogen oxide emissions (about 50%) comes from cars, buses, and other forms of transportation. Nitric oxide, NO, forms in small quantities in the cylinders of internal combustion engines in the reaction 

As noted in the Chemistry Put to Work box in Section 15.7, the equilibrium constant for this reaction increases from about 10 at 300 K to about 0.05 at 2400 K (approximate temperature in the c 4inder of an engine during combustion). Thus, the reaction is more favorable at higher temperatures. In fact, some NO is formed in any high-temperature combustion. As a result, electrical power plants are also major contributors to nitrogen oxide pollution. 

Before the installation of pollution-control devices on automobiles, typical emission levels of NO, were 4 grams per mile. (The x is either 1 or 2 because both NO and NO2 are formed, although NO predominates.) Starting in 2004, the auto emission standards for NO,(. called for a phased-in reduction to 0.07 g/mi by 2009, which was achieved. 

In air, nitric oxide is rapidly oxidized to nitrogen dioxide  

The equilibrium constant for this reaction decreases from about 10 at 300 K to about 10 at 2400 K. 

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See the Chemistry in Use essay Nitrogen Oxides and Photochemical Smog in Chapter 24. 

Nitrogen Oxides and Photochemical Smog The extremely reactive O radicals combine with O2 to pro-... 

See the Chemistry In Use essay "Nitrogen Oxides and Photochemical Smog"ln Chapter 28. 

Dimitriades, B. Effects of hydrocarbon and nitrogen oxides on photochemical smog formation. Environ. Sci. Technol. 6 253-260, 1972. 

Maeda Y, Kada N, Suetaka T, et al. 1988. Formation of aldehydes in reactions of hydrocarbons and nitrogen oxides in photochemical smog. Chem Express 3 259-262. 

Nitrogen Oxide. The photochemical smog reaction involves nitrogen oxides, hydrocarbons, and sunlight. The global importance of this pollutant system depends upon the amounts of materials emitted to the atmosphere, their residence time in the atmosphere, and their reaction products. 

Smog A mixture of smoke and tog, that arises from nitrogen oxides and hydrocarbons and the photochemical action of sunlight. 

In the early 1950 s, it was reported by Haagen-Smit that many of the characteristics of photochemical smog could be explained by the presence of ozone and other photochemical oxidants. These substances, he believed, were formed in the atmosphere as a result of chemical reactions involving nitrogen oxides and hydrocarbons present in automobile exhaust. Significant quantities of nitrogen oxides were also emitted by power plants. 

Atmospheric pollution caused by SO compounds from the combustion of fossil fuels, O3, CO2, volumetric CH compounds, and NO has become as matter of growing world wide concern in recent years. Nitrogen oxides contribute to acid rain and photochemical smog, and they can cause respiratory problem. Therefore, nitrogen oxides should be controlled and removed from the source in order to keep the earth clean and as-received for our health [1-3]. 

In Europe oxidants were first observed in the Netherlands in the late 1960 s (14). Before then many believed that photochemical smog could only be found at lower latitudes with more intense solar radiation. Later experience has shown that if the emissions of nitrogen oxides and organic components are large enough, photochemical oxidants can be produced anywhere during the summer season. A simultaneous increase in the ozone concentrations has on several occasions been observed all over western Europe (15). 

The emissions from smoldering combustion contain all the necessary compounds needed for the formation of photochemical smog. We have mentioned in Chapter 3 that four main components are necessary for the initiation of this tropospheric phenomenon sunlight, temperature above 18 °C, hydrocarbons and nitrogen oxides, and all of them are present during forest fires in Southeast Asia. 

Photochemical smog air pollution produced by the action of light on oxygen, nitrogen oxides, and unburned fuel from auto exhaust to form ozone and other pollutants. 

Heterogeneous catalysis plays a major role in the fight against urban air pollution. Two components of automobile exhausts that help form photochemical smog are nitrogen oxides and unburned hydrocarbons. 

Describe the origins and behavior of sulfur oxides and nitrogen oxides as air pollutants, including the generation of add rain and photochemical smog. (Section 18.2)... 

Atomic oxygen can also react with hydrocarbons to form other chemicals that are toxic and also impart an odor to the air. On a sunny day only about 0.2 ppm of nitrogen oxides and 1 ppm of reactive hydrocarbons are sufficient to initiate these photochemical smog reactions. The hydrocarbons involved in these reactions come mostly from unburned petroleum products such as gasoline, and the nitrogen oxides come from the exhausts of internal combustion engines. 

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