Nitrogen is a chemical element on the periodic table, with the symbol N and atomic number 7. It is a nonmetallic element, very light, and is a diatomic element because its atoms appear in pairs. In its gaseous state, nitrogen is represented as N2 and makes up 78% of the Earth's atmosphere.
Nitrogen is used to make amino acids, which in turn make the proteins essential for all organisms. Nitrogen is also a part of the nucleic acids that make up our DNA and RNA. These functions make nitrogen fundamental to life and cellular processes.
Nitrogen in its molecular form, N2, is not damaging to the environment. It might be confusing, then, when we talk about reducing nitrogen levels in the environment because they're causing harm. The nitrogen that's toxic to the environment in excess amounts is termed "reactive nitrogen", which is nitrogen in alternate forms. For example, one atom of nitrogen combines with three oxygen atoms to form nitrate (NO3-), which is linked to eutrophication of water. Nitrogen monoxide (NO) and nitrogen dioxide (N2O) are also toxic forms of reactive nitrogen and contribute to air pollution. Other forms of reactive nitrogen include nitrous oxide (N2O), which is a greenhouse gas, ammonia (NH3), which is essential to the Haber-Bosch process, critical to mass agriculture, and ammonium (NH4+). These forms of reactive nitrogen are linked to negative environmental consequences such as eutrophication, anoxia, and the greenhouse effect, among others. To learn more about the negative consequences of reactive nitrogen in the environment, check out this article by Michigan State University.
Therefore, when the NWG discusses reducing limiting the University's nitrogen footprint, we are not endeavoring to reduce the amount of nitrogen in the atmosphere, rather the damage the environment incurs through an excess of reactive nitrogen stemming from human activities.