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The gases that surround a star or planetary body are held in place by gravity and are referred to as the atmosphere. If gravity is high and the temperature of the atmosphere is low, a body is more likely to keep an atmosphere over time.

Atmospheric fixation, industrial fixation, and biological fixation are the three methods for utilising atmospheric nitrogen. The following paragraphs detail each procedure.

Human activity is a significant contributor to the overall quantity of fixed nitrogen in the atmosphere. Artificially manufactured nitrogen-based fertiliser (ammonia, urea, ammonium salts) is taken up by plants and enters the biosphere.

The considerable rise in vehicle traffic also contributes to total nitrogen fixed, as high engine running temperatures resemble lightning, causing$\mathrm{NO}$to develop from the air taken in to burn the hydrocarbon fuel. Overuse of fertilisers and cars are major sources of water contamination. Nitrate from fertiliser and vehicle operation leaches into natural waters, causing eutrophication鈥攖he depletion of oxygen and the death of aquatic animal life鈥攁s a result of excessive algal and plant growth and degradation.

a. Atmospheric fixation entails high-temperature endothermic processes including the conversion of ${\mathrm{N}}_2$and ${\mathrm{O}}_2$to $\mathrm{NO}$which is then oxidised exothermically by ozone to generate ${\mathrm{NO}}_2$.${\mathrm{NO}}_2$interacts with a hydroxyl radical to generate ${\mathrm{HNO}}_3$during the day.

$$\begin{gathered} {\mathrm{N}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)鈫�2\mathrm{NO}\left(\mathrm{g}\right) \\ \mathrm{NO}\left(\mathrm{g}\right)+{\mathrm{O}}_3\left(\mathrm{g}\right)鈫�{\mathrm{NO}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right) \\ {\mathrm{NO}}_2\left(\mathrm{g}\right)+\mathrm{HO}脳\left(\mathrm{g}\right)鈫�{\mathrm{HNO}}_3\left(\mathrm{g}\right) \end{gathered}$$

The acid is then carried down by rain and enters both the sea and the land as ${\mathrm{NO}}_3^{-}$, which plants can use.