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Nitrogen oxides (NOx = NO + NO2) emitted from a stationary combustion chamber (including waste to energy plants) or engines cause numerous undesirable environmental effects. These include negative influences on human and animal health, detrimental effects on plants and vegetation, acid rain, and smog. These negative influences are commonly accepted by the scientific community. However, the impact of NOx on the greenhouse effect (GHE) is not generally accepted by the scientific community.
Warming | Cooling | Cross Impact |
---|---|---|
Air | ||
In the short-term, NOx emissions contribute to warming by enhancing tropospheric O3 concentrations (on a daily time scale), which are recognized as GHG [2][5]. | NOx enhances OH production. CH4 (GHG) is oxidized in the presence of OH [2][14]. NOx can lead to decreases in O3 concentration on a decadal time scale because it causes an increase in OH radical concentration, which decreases CH4 concentration, which decreases NO2 formation, which decreases O3 formation. [2][14]. 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 [2][10]. |
NOx leads to O3 decreasing (on a decadal time scale) or increasing (on a daily time scale) [2]. |
Soil and vegetation aboveground | ||
Nitrogen is a substrate for N2O production by nitrifying and denitrifying bacteria in soils. Thus, the deposition of nitrogen (Nr) onto ecosystems can increase N2O emissions and decrease the uptake of atmospheric CH4 by soil microorganisms. Soil microbes that consume CH4 often preferentially consume ammonium (NH4+), leading to reduced CH4 consumption rates in the presence of abundant NH4+ [2]. Inhibition of photosynthesis and a reduction of atmospheric CO2 sequestration by the plant biomass due to an increase of O3 concentration in the atmosphere (impacted by NOx). Reduction of aboveground C storage and reduction of belowground C assimilation and allocation [1][2] In some cases, the excess of N leads to the enhanced mortality of plants due to nutrient imbalances or acidification [2]. |
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 CO2 uptake into plant biomass. N additions to soil typically increase C capture and storage [2]. Foliar N may also increase the albedo of the canopy, enhancing the reflectivity of the Earth’s surface, and hence contributing to cooling [2]. |
Warming and cooling effects are possible. The effect of N on net C flux (both above and below ground pools) differs among ecosystems [1][2]. |
Water | ||
Nitrogen is a substrate for N2O production by nitrifying and denitrifying bacteria in water bodies [2]. Denitrification occurring in water can emits N2O [15]. Nitrous oxide (N2O) can be emitted from wastewater treatment processes [15][16][17]. Both SO2 and NO inhibited algal growth at a high level of CO2 [18][19]. |
N- water can accelerate to grow algae growth. Nevertheless, the harmful (toxic, food-web altering, hypoxia-generating) algal blooms (HABs) have been linked to human nutrient (phosphorus (P) and nitrogen (N)) over enrichment [20] The serious problem is cyanobacterial bloom formation. Decreasing P and N loads can counteract the direct positive effect of warming temperatures on bloom proliferation [21][22]. Some algae species can sequestrate the CO2 from the flue gas including SOX and NO [23]. In the case of some species (green alga Chlorella sp.), the presence of NOx can enhance algae growth [24] |
NOx and SOx might be beneficial to the growth of microalgae as they can provide additional nutrients. However, this is true only when the culture pH is stably controlled and the NOx/SOx concentrations should be lower than the inhibitory level [25]. |