# On the Issues of \(\mathbf{NO_{x}}\) as Greenhouse Gases: An Ongoing Discussion...
## 2 The Role of NO\({}_{\rm x}\) in the Greenhouse Effect  
It has been previously mentioned that different opinions exist within the scientific community about the role of NO\({}_{\rm x}\) in the GHE. This inconsistency existed in historical scientific papers as well as in currently published issues (i.e., in 2022). Some researchers directly include NO\({}_{\rm x}\) in GHGs or they suggest that NO\({}_{\rm x}\) are GHGs, but do not explain the nature of this impact [11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21]. Some researchers do not distinguish precisely between N\({}_{\rm 2}\)O and NO\({}_{\rm X}\), or they even include N\({}_{\rm 2}\)O into NO\({}_{\rm x}\)[22; 23; 24; 25; 26], suggesting that NO\({}_{\rm x}\) are GHGs. Indeed, N\({}_{\rm 2}\)O is created during the combustion process. Higher concentrations of N\({}_{\rm 2}\)O can be found be in flux gas when the flame temperature is lower than 900 \({}^{\circ}\)C such as in fluidized-bed combustors [27]. Furthermore, N\({}_{\rm 2}\)O is recognized as a by-product during NO formation [28]. However, it has already been explained that the inclusion of N\({}_{\rm 2}\)O into NO\({}_{\rm x}\) is not a true assumption. Conversely, in some scientific articles, the impact of NO\({}_{\rm x}\) on the GHE is not highlighted, and only other environmental negative effects of NO\({}_{\rm x}\) are mentioned [29; 30; 31]. The role of NO\({}_{\rm x}\) in the GHE should be explained. It is very important to distinguish between two crucial issues. The potential possibility of NO\({}_{\rm x}\) influencing the GHE is not equal to including these gases in direct GHGs. Very often in scientific articles, these two issues are confused, and this distinction is not clearly presented. It should be explained that NO\({}_{\rm x}\) (NO\({}_{\rm x}\) = NO + NO\({}_{\rm 2}\)) do not directly influence radiative heat transfer (from the Sun to the Earth's surfaces) in the radiation spectra typical for direct GHGs (such as CO\({}_{\rm 2}\), CH\({}_{\rm 4}\), and N\({}_{\rm 2}\)O). The GHE is caused by the balance between radiative heat transfer from the Sun (average surface temperature of 6000 K, and wavelength of 0.2-4 \(\upmu\)m) to the Earth's surface and the radiative heat transfer from Earth (average surface temperature 255 K, and wavelength of 4-100 \(\upmu\)m) to space. The GHGs existing in the atmosphere (such as H\({}_{\rm 2}\)O and CO\({}_{\rm 2}\)) weakly absorb radiation of a 0.2-4 \(\upmu\)m wavelength and strongly absorb radiation of 4-100 \(\upmu\)m, thus the Earth's surface is warmed. Part of the energy received from sunlight irradiation is accumulated on the Earth's surface because of the impact of GHGs. This is because radiative heat transfer from the Sun is transferred by the atmosphere, whereas the radiative heat emitted from the Earth's surface is captured due to the impact of GHGs. This phenomenon is called the greenhouse effect. It causes increases and stabilization of the temperature on the Earth's surface during the day and night. A lack of atmosphere and a deficiency of the GHE would result in a decrease of the temperature on Earth to an average value of \(-\)18 \({}^{\circ}\)C, whereas the actual average temperature on Earth is +15 \({}^{\circ}\)C. The GHE created specific conditions, allowing our planet to be habitable and to develop life [32]. The direct GHGs are H\({}_{\rm 2}\)O, CO\({}_{\rm 2}\), CH\({}_{\rm 4}\), N\({}_{\rm 2}\)O, fluorine compounds (such as NF\({}_{\rm 3}\) and SF\({}_{\rm 6}\)), and chlorine compounds (such as CFCl\({}_{\rm 3}\) and CF\({}_{\rm 2}\)Cl\({}_{\rm 2}\)) [32; 33]. A more particular list of direct GHGs was presented by [PERSON] et al. [33]. At this stage, it is necessary to mention the term atmospheric window. There is a region containing a long-wave spectrum from approximately 8 \(\upmu\)m to 12 \(\upmu\)m known as the atmospheric window, where absorption by water and CO\({}_{\rm 2}\) is weak (see Figure 2).