# On the Issues of \(\mathbf{NO_{x}}\) as Greenhouse Gases: An Ongoing Discussion...
## 5 Simplified Evaluation of NOx (Surface Sources) Impact on GHE

Table 2: _Cont._estimated for central latitudes [33] and the highest NO\({}_{\rm x}\) emissions are observed for such regions [67]. Nevertheless, it should be noted that for surface sources, the global GWP\({}_{100}\) = \(-\)11 [33]. Moreover, it is assumed that the contribution of emitted CO\({}_{2}\) from fossil fuel usage and industrial processes in the GHE is 65% compared to the impact of all direct GHGs [68]. Based on this assumption, the impact of NO\({}_{\rm x}\) on the GHE compared to CO\({}_{2}\) can be described by the coefficient %GHG\({}_{\rm NO_{x}}\) (9). \[\%\rm{GHG}_{\rm NO_{x}}=NO_{x-eq,CO2}/(NO_{x-eq,CO2}+CO_{2})\times 100\% \tag{9}\]  
Furthermore, the impact of NO\({}_{\rm x}\) on the GHE compared to all direct GHGs (%(total)GHG\({}_{\rm NO_{x}}\) is  
\[\%\rm{(total)GHG}_{\rm NO_{x}}=NO_{x-eq,CO2}/(NO_{x-eq,CO2}+CO_{2}/0.65)\times 1 00\% \tag{10}\]  
The NO\({}_{x-eq,CO2}\) parameter is the sum of the emitted NO\({}_{\rm x}\) (Gt/year) multiplied by GWP\({}_{100}\) for NO\({}_{\rm x}\). In other words, NO\({}_{x-eq,CO2}\) is the emission of NO\({}_{\rm x}\) as an equivalent of CO\({}_{2}\) (regarding the GHE) at an assumed time horizon. It can be seen from Table 2 that the participation of NO\({}_{\rm x}\) in the GHE regarding CO\({}_{2}\) impact and the most pessimistic scenario does not exceed 5%. In the case of the most realistic scenario (NO\({}_{\rm x}\) GWP\({}_{100}\) = 1.6), this value does not exceed 1%. If the total direct GHGs emissions are considered (meaning the emission of CO\({}_{2}\)/0.65), the NO\({}_{\rm x}\) contribution to the GHE does not exceed 2.8% and 0.5% for the most pessimistic (GWP\({}_{100}\) = 10) and the most realistic (GWP\({}_{100}\) = 1.6) scenarios, respectively. Although the presented analysis is simplified, it allows for an estimation of the impact of NO\({}_{\rm x}\) from surface sources on the GHE. Thus, even a pessimistic scenario assumes this impact is not large compared to CO\({}_{2}\) and other direct GHGs. Moreover, assuming the values of NO\({}_{\rm x}\) emissions from a combustion of 0.038 GtN/year, provided by [PERSON], [PERSON], and [PERSON] [69], the impact of NO\({}_{\rm x}\) on the GHE is weaker. This is consistent with the conclusions of [PERSON] et al. [70]. Furthermore, they noticed that NO\({}_{\rm x}\) emissions, O\({}_{3}\) as well as particulate matter, and SO\({}_{\rm x}\), which are not the major concern in climate change and perspectives, are threatening the air quality and premature deaths (<75 years). Considering the emission of NO\({}_{\rm x}\) from coal-fired units (power plants and combined heat and power (CHP) plants only), the participation of NO\({}_{\rm x}\) in the GHE is lower. It is known that the maximal NO\({}_{\rm x}\) emission per capacity from such units is 1.8 kg NO\({}_{\rm x}\)/MW when cold type start (i.e., start time >48 h since plant shutdown) is considered [71]. The capacity of coal-fired units in 2019 was estimated at 2087 GW/year [72]. Thus, the total NO\({}_{\rm x}\) emissions from such sources is 0.00376 GtNO\({}_{\rm x}\)/year. The estimated installed capacity of coal-fired units was compared with the estimation presented by [PERSON] and co-workers [73] According to their estimation, a combined installed capacity of biomass- and fossil-fuel-burning power plants operating worldwide in 2010 was 3570 GW. Nevertheless, the global NO\({}_{\rm x}\) emissions (in 2010) from these sources was 0.0252 GtNO\({}_{\rm x}\)/year. However, comparing these values with the data presented in Table 3, it is clear that the maximal impact of NO\({}_{\rm x}\) emitted from solid fuel-fired sources is less than 1% compared with direct GHGs. Finally, [PERSON] and co-workers [74] reported that anthropogenic NO\({}_{\rm x}\) emissions dropped by at least 15% globally and 18 to 25% regionally in April and May 2020 due to the pandemic influence. Similar observations were presented by [PERSON] and co-workers [75].