About 40 percent of the human population depends upon food production made possible by synthetic nitrogen fertilizers.

Combustion of fossil fuels adds more reactive nitrogen to air, water and soil. This distortion of the global nitrogen cycle due to excessive reactive nitrogen in the environment, while raising agricultural yields, causes degradation of water and air quality, biodiversity, ecosystem services and human health. Meanwhile, reactive nitrogen deficiencies on farmland in many developing countries continue to create economic and health hardships, and accelerate land degradation.

Prepared jointly by the United Nations Environment Programme (UNEP) and the Woods Hole Research Center, with significant contributions from the International Nitrogen Initiative (INI), this non-technical report on reactive nitrogen in the environment summarizes the present scientific understanding of the major issues surrounding reactive nitrogen, and discusses the overarching environmental, human health, and economic issues created by both excesses and deficiencies. The report also provides case studies of effective policy implementation and reviews emerging policies to show how negative impacts associated with reactive nitrogen may be successfully addressed locally, nationally, and regionally, given similar challenges, shared experiences, and effective solutions.

This review is intended to assist all stakeholders in understanding and assessing these challenges, and sets out the sources and impacts of reactive nitrogen and current trends in use and emissions. Recommendations are made on the assessment, monitoring, information sharing and collaboration required at different geographical scales, and across disciplines and jurisdictions, to develop and implement coherent and effective policies to address nitrogen excess and deficiency.