The Nitrogen Cycle

Nitrogen makes up 78% of the Earth's atmosphere, but this form of nitrogen (N 2 ) is inert. All

other species of nitrogen are called reactive forms of nitrogen. Reactive nitrogen in the

environment is the type of nitrogen that causes impacts to environmental and human health;

N 2  is generally considered to be inert and therefore does not react with the environment in the

same ways. Examples of reactive nitrogen include the greenhouse gas nitrous oxide (N 2 O),

nitrogen oxides (NOx), ammonia (NH 3 ), nitrate (NO 3 - ), and nitrite (NO 2 - ) (Galloway et al. 2008).