This project evaluated the sensitivity of all Inventory and Monitoring (I&M) national parks in the United States to potential nutrient enrichment effects caused by atmospheric nitrogen (N) deposition. Such effects can be caused by the addition of oxidized N (NOx) and/or reduced N (NHx) to natural ecosystems. Nutrient N enrichment can occur in both terrestrial and aquatic ecosystems. The addition of N from air pollution sources to national park ecosystems can alter plant and algal communities and influence the mix of species that thrive in those ecosystems. This assessment includes consideration of three factors that influence nutrient enrichment risk to park resources from atmospheric N deposition: N pollutant exposure, inherent ecosystem sensitivity, and park protection mandates. National parks and networks are ranked according to each of these themes. An overall risk ranking is calculated based on averages of the three theme rankings.