Improved Understanding of the Nitrogen Cycle


The nitrogen cycle has important implications for air quality and climate in addition to fisheries and marine ecosystems. Anthropogenic activities have perturbed the natural nitrogen cycle, with major effects on the atmosphere and marine systems. Scientists are working to understand these changes to help society adapt to a changing nitrogen cycle.

The term “reactive nitrogen” (Nr) refers to nitrogen that has been oxidized or reduced. Nr is present in compounds that are cycled through the atmosphere and biosphere through chemical changes and biological processes. These compounds include nitrogen oxides (NOx), ammonia (NH3), and nitrous oxide (N2O). Anthropogenic activities such as fertilizer use and fossil fuel combustion have greatly increased the production of Nr. Because of the contribution of these compounds to tropospheric ozone and aerosols, and because nitrous oxide is a potent greenhouse gas, the anthropogenic effects on the nitrogen cycle will have an uncertain effect on radiative forcing. Atmospheric reactive nitrogen is also important for marine systems due to nitrogen deposition.

AC4 Activities

AC4 supports research regarding atmospheric Nr and its interactions with terrestrial and marine systems. Specifically, current projects examine aspects of Nr cycling such as sources and sinks, chemical changes and chemical properties, and interactions with weather, climate, and air quality. Data is collected through remotely sensed and in situ observations as well as laboratory experiments and modeling.

Descriptions of these projects can be found in the Funded Projects section of the website

Contact AC4

Dr. Ken Mooney
Program Manager, Atmospheric Chemistry, Carbon Cycle, & Climate (AC4)
P: (301) 734-1242
F: (301) 713-0517

Dr. Monika Kopacz (UCAR)
Program manager, Atmospheric Chemistry, Carbon Cycle and Climate (AC4)
P: (301) 734-1208

  • Join AC4's Mailing List


Climate Program Office
1315 East-West Hwy, Suite 1100
Silver Spring, MD 20910


Americans’ health, security and economic wellbeing are tied to climate and weather. Every day, we see communities grappling with environmental challenges due to unusual or extreme events related to climate and weather. In 2017, the United States experienced a record-tying 16 climate- and weather-related disasters where overall costs reached or exceeded $1 billion. Combined, these events claimed 362 lives, and had significant economic effects on the areas impacted, costing more than $306 billion. Businesses, policy leaders, resource managers and citizens are increasingly asking for information to help them address such challenges.