# On the Issues of \(\mathbf{NO_{x}}\) as Greenhouse Gases: An Ongoing Discussion...
## 1 Introduction  
### \(\mathbf{NO_{x}}\) Environmental Impact  
Nitrogen oxides (NO\({}_{x}\) = NO + NO\({}_{2}\)) are emitted from natural and man-made (anthropogenic) sources. One of the main anthropogenic sources of NO\({}_{x}\) emissions is combustion processes realized in stationary chambers (such as boilers) and vehicle engines. The existence of NO\({}_{x}\) in the atmosphere causes many environmental problems such as acid rain and photochemical smog. Both of these have a negative influence on human and animal health and cause disturbances in plants and vegetation [1, 2]. However, there are some positive applications of nitrogen oxides. For example, nitric oxide (NO) is used in medicine as an inhalation agent (concentration dose in the range of 1-80 ppm) for children and adults suffering from circulatory and respiratory problems [3]. Furthermore, NO is also applied as an antimicrobial agent [4]. It should be explained that the toxicity of NO\({}_{x}\) results from the fact that primarily emitted NO is converted to NO\({}_{2}\), which belongs to the group of highly toxic gases [3].  
Currently, there is a debate in the scientific community concerning the impact of NO\({}_{x}\) on the greenhouse effect (GHE). Some scientists unambiguously cite NO\({}_{x}\) as a greenhouse gas (GHG), placing this compound beside direct GHGs such as CO\({}_{2}\), CH\({}_{4}\), N\({}_{2}\)O, and hydrofluorocarbons (HFCs) (see [PERSON]'s graphics in Figure 1).  
The opinions regarding the impact of NO\({}_{x}\) on the GHE are unclear in the scientific community. There appear to be inconsistent views on whether NO\({}_{x}\) influences the GHE, and on the nature of this influence. Despite the proliferation of relevant investigations, a range of different opinions can be observed, and some confusion exists within the scientific literature. Therefore, it is necessary to present a synthesis of existing opinions. This willinvolve appropriate interpretation, consistent with the current knowledge in the field, of the role NOx play in the GHE. From the different opinions presented in the scientific literature, some common characteristic views can be classified as follows:  
* NOx are GHGs and influence global warming;
* NOx are not GHGs and do not influence the GHE;
* NOx are indirect GHGs and influence global warming;
* NOx are indirect GHGs and influence global cooling.  
Thus, in this paper, the issue of NOx impact on the GHE is discussed, and an investigation into the nature of this impact was conducted. [PERSON] et al. [5] in 2011 and [PERSON] et al. [6] in 2013 showed the complex analysis of nitrogen-species emission (including NOx) on GHE. Instead of these analyses, the role of NOx in GHE is still discussed. In the current paper, the role of CO in NOx conversion is underscored, and the mechanism of warming and cooling effects is presented in terms of the role of NOx in the GHE. New insights and investigation results related to the role of NOx in the GHE and the reason for misunderstanding the role of NOx-GHE role is presented. The different opinions on the role of NOx in GHE are discussed. Eventually, this paper underscores the necessity of debate about the role of NOx in the GHE. The seriousness of this debate is especially important now when the world is faced with dramatic challenges related to global warming. (compare the document: \"A Clean Planet for all. A European long-term strategic vision for a prosperous, modern, competitive and climate neutral economy\" [[https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/uri=CELEX](https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/uri=CELEX)]([https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/uri=CELEX](https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/uri=CELEX)): 52018 DC0773&from=EN (accessed on 1 October 2022))