# On the Issues of \(\mathbf{NO_{x}}\) as Greenhouse Gases: An Ongoing Discussion...
## 4 Dualistic Nature of NO\({}_{x}\) Impact on the Greenhouse Effect
### Summary  
It has already been mentioned that the warming and cooling effects of NO\({}_{\rm x}\) in the atmosphere are possible due to the impact of different processes. The warming and cooling effects are summarized in Table 2. These effects were divided into three groups in terms of the influence area (i.e., air, water, soil, and vegetation aboveground). Some processes seem to be opposing. Thus, examples of these cases are described in a \"cross-impact\" column.  
In some cases, inputs of Nr from atmospheric deposition enhance plant growth rates because of the fundamental constraint of N availability on plant productivity and CO\({}_{2}\) uptake into plant biomass. N additions to soil typically increase C capture and storage [6].  
Foliar N may also increase the albedo of the canopy, enhancing the reflectivity of the Earth's surface, and hence contributing to cooling [6].  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Warming** & **Cooling** & **Cross Impact** \\ \hline \hline  & Air & \\ \hline  & NO\({}_{\rm x}\) enhances OH production. CH\({}_{4}\) (GHG) is & \\  & oxidized in the presence of OH [6; 39]. & \\  & NO\({}_{\rm x}\) can lead to decreases in O\({}_{3}\) concentration on a & \\  & decadal time scale because it causes an increase in & \\  & In the short-term, NO\({}_{\rm x}\) emissions contribute to & OH radical concentration, which decreases CH\({}_{4}\) & \\  & warming by enhancing tropospheric O\({}_{3}\) & concentration, which decreases NO\({}_{2}\) formation, & \\  & concentrations (on a daily time scale), which & which decreases O\({}_{3}\) formation. [6; 39]. & \\  & are recognized as GHG [6; 32]. & The formation of fine particles called aerosols. & \\  & Aerosols are powerful cooling agents, both directly & \\  & by scattering or absorbing light, and indirectly by & \\  & affecting the cloud formation, their lifetime, and & \\  & brightness [6; 7]. & \\ \hline  & Soil and vegetation aboveground & \\ \hline \hline Nitrogen is a substrate for N\({}_{2}\)O production by & & \\  & nitriving and denitrifying bacteria in soils. & \\  & Thus, the deposition of nitrogen (Nr) onto & \\  & ecosystems can increase N\({}_{2}\)O emissions and & \\  & decrease the uptake of atmospheric CH\({}_{4}\) by soil & \\  & microorganisms. Soil microbes that consume & \\  & CH\({}_{4}\) often preferentially consume ammonium & \\  & (NH\({}_{4}\)+), leading to reduced CH\({}_{4}\) consumption & \\  & rates in the presence of abundant NH\({}_{4}\)+ [6]. & \\  & Inhibition of photosynthesis and a reduction of atmospheric CO\({}_{2}\) sequestration by the plant & \\  & biomass due to an increase of O\({}_{3}\) concentration & \\  & in the atmosphere & \\  & Reduction of aboveground C storage and & \\  & reduction of belowground C assimilation and & \\  & allocation [5; 6] & \\ \hline In some cases, the excess of N leads to the & & \\  & enhanced mortality of plants due to nutrient & \\  & imbalances or acidification [6]. & \\ \hline \hline \end{tabular} In some cases, inputs of Nr from atmospheric deposition enhance plant growth rates because of the fundamental constraint of N availability on plant productivity and CO\({}_{2}\) uptake into plant biomass. N additions to soil typically increase C capture and storage [6].  
Foliar N may also increase the albedo of the canopy, enhancing the reflectivity of the Earth’s surface, and hence contributing to cooling [6].  
\end{table}
Table 2: The summary of the warming and cooling effect of NO\({}_{\rm x}\) in terms of the influence on the area.