With the beginning of the century, there has been an increasing concern for the health of the planet. The scientist and the government work hard to try to make changes in the environment. There was a feeling that without the world, no life and therefore it was necessary to save the world. As nations continue to industrialize, it is increasingly difficult to reduce emissions of greenhouse gases and hazardous toxins that are destructive to the world to stop. One such toxin called NOx. NO is nitric oxide and nitrogen dioxide NO2. Both are in different parts of the concentrations of NOx. Normally, people have no idea about that because not only NOx is colorless, but has no smell. This neglect can be released into the environment. There are many places that emissions of nitrogen oxides. Almost half of these emissions come directly from the cars. Early in the century, many people drive around in big SUVs that high consumption of gas did nothing more than an increase in these emissions to produce. Ironically, the economic crisis has shaped society in a more green friendly nation. But what kind of hydrocarbon gas for use some form of NOx. Typically, most are found to be NO.Often Sometimes people wonder why this matters. They do not assess the environmental concerns associated with NOx. The main concern is the impact of NOx in the human respiratory system. NO combines with ammonia leading to the formation of nitric acid, which is a very strong acid that can do a lot of serious bodily harm. Small particles in the lungs and get holes in them, which could lead to a fatal outcome. There are things that are done to try to prevent the NOx that too much of a problem. In some areas, the catalytic reduction one of the main instruments used is selective. What this means in non-technical terms, the creation of elemental nitrogen and water. None of that harm the environment. In more technical terms, urea is used in the engine and then broken down into ammonia. The products of this reaction, after having passed through a catalyst to elemental nitrogen and water. The SCR catalyst is shown to make a considerable amount of work on the reduction of NOx. But there are other ways, but that can be used to treat the NOx concentrations in the environment decrease. One is the use of engine management, as its name suggests, is to control the amount of emissions from an engine. There are fewer emissions released, but the engine runs less efficiently resulting in the structure of soot. A final method is a trap catches of NOx and NOx storage catalytic NOx then put that through acts of the reduction of N2 and CO2 basic skills. Nitrogen in its elemental form, is not harmful to the environment. While CO2 can harm the environment is not as harmful as the NOx gases released by cars. CO2 is the lesser of two evils.What these three techniques have in common is that they all seek to reduce NOx. However, the SCR catalyst is only that it has been shown that the greatest impact on reducing the concentration levels of NOx. There is no concern of reduced efficacy of the car and there is no need for a lesser of two evils approach because most of the NOx is converted to elemental nitrogen and water. The only problem is that there is a form of urea in the system. If that happens, this is definitely an effective technique tool.Each has its ups and downs. Some work better than others (SCR), but even that has its negative aspects. It is important to determine the cost to productivity ratio is that car companies are willing to spend. What is too much? What is clear is that the environment is growing more and when people are really worried about him, who must take the necessary measures to prevent further degradation if it means taking a little more money to spend, that can course of action required.