Nitrogen oxides, environmental concern

Emissions of nitrogen oxides and sulfur oxides from combustion systems constitute important environmental concerns. Sulfur oxides (SO ), formed from fuel-bound sulfur during oxidation, are largely unaffected by combustion reaction conditions, and need to be controlled by secondary measures. In contrast, nitrogen oxides (NO ) may be controlled by modification of the combustion process, and this fact has been an important incentive to study nitrogen chemistry. Below we briefly discuss the important mechanisms for NO formation and destruction. A more thorough treatment of nitrogen chemistry can be found in the literature (e.g., Refs. [39,138,149,274]). 

Concerns about the environmental effects of emissions resulting from the combustion of fossil fuels, particularly coal, continue to increase as the utilization of these fuels grows. The large amounts of sulfur dioxide and nitrogen oxides emitted into the atmosphere and the attempts to tie these fossil-fuel-derived pollutants directly to the undeniably difficult problem of acid rain have caused heated debates, numerous research studies, government actions, and serious efforts to reduce pollution. The issues are extremely complex, and our understanding of the origin, properties, behavior, and effects of these pollutants is incomplete. Often, theories are contradictory. 

Since the mid-1970 s, increasing interest has emerged in the environmental consequences of the large scale deposition of atmospheric contaminants. The deposition of acid-forming constituents, sulfate and nitrate, is of particular concern for potentially adverse ecological effects. These species derive from the oxidation of sulfur dioxide (SO ) and nitrogen oxides (NO and NO ). Over most if... 

Over the same period, emissions of nitrogen oxides (NOx) were predicted to remain at current levels or to increase, depending specially on the growth of motor vehicle transport. Such predictions were not initially viewed with any sense of environmental concern because of the accepted nutrient properties of deposited nitrogen and its possible fertilizing action on the terrestrial environment. However, as... 

The emission of nitrogen oxides (NOx) from automotive and stationary sources causes serious environmental concern. Automotive exhaust gas aftertreatment systems are commonly based on precious metal catalysts (three way or diesel oxidation catalysts). One undesired effect during NOx reduction with these catalysts is the formation of N2O, which is now considered to be an environmental pollutant also [1,2], In this report the generation of N2 and N2O during NOx decomposition or reduction on Pt/alumina is investigated. 

The past few years have seen a flurry of activity in research into the photoelimination of NOx species, particularly on account of the biological activity of NO as well as interest in the environmental impact of nitrogen oxides. In the period under review at present, however, only three reports concerning photoelimination of NO or NO2 have appeared. 

The emission of gaseous pollutants such as sulfur oxide, nitrogen oxide, and toxic gases as a result of a variety of industrial processes has become a serious environmental concern, especially in specific parts of the world. As a result, sensors are needed to monitor the concentration of various contaminants, which can prevent or limit uncontrolled releases of toxic compounds. 

A major concern in the present day combustion of coal is the performance of the process in an environmentally acceptable manner through the use of a variety of environmentally acceptable technologies such as the use of a low-sulfur coal or through the use of post-combustion cleanup of the off-gases (Chapter 23). Thus, there is a marked trend in the modem research to more efficient methods of coal combustion. In fact, the ideal would be a combustion system that is able to accept any coal without a precombustion treatment, or without the need for post-combustion treatment, or without emitting objectionable amounts of sulfur and nitrogen oxides and particulates. To dream, to dream, perchance to dream. 

Environmental concerns and strict pollution legislation prompted action in the construction of up to date coal-fired boilers and adaptation of existing plants. At the present time, flue gas desulfurization is the only conventional method employed on a commercial scale for reducing sulfur emissions after coal combustion. Over 90% reduction of sulfur dioxide in flue gases can be achieved by this process. Combustion control techniques of the flames will effectively reduce oxides of nitrogen emissions into the atmosphere. 

The reservoir of free N2 in the atmosphere is so vast that human activity cannot appreciably alter its amount, and adequate means are at hand for ensuring plentiful supplies of fixed nitrogen for agricultural and industrial purposes. The major environmental question concerning nitrogen at present relates to the role of nitrogen oxides generated by industry and automobile exhaust as contributors to the increased acidity of rainfall. 

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