1) High energy N fixation of atmospheric N2 gas to form nitrate and ammonium to be used as fertilizers.
2) The high rates of fossil fuel combustion has increased the amount of NO and N2O in the atmosphere, which are very effective green house gases and form ozone in the atmosphere that we breath.
3) The cultivation of leguminous plants (beans) and N fixing species (Alder) in agricultural settings. These plants have increased nitrate pollution in ag settings