Atmospheric ammonia (NH3) has increased dramatically as a consequence of the production of synthetic nitrogen (N) fertilizer and proliferation of intensive livestock systems. It is a chemical of environmental concern as it readily reacts with atmospheric acids to produce fine particulate matter and indirectly contributes to nitrous oxide (N2O) emissions. Here, we present the first tall tower observations of NH3 within the U.S. Corn Belt for the period April 2017 through December 2018. Hourly average NH3 mixing ratios were measured at 100 and 56 m above the ground surface and fluxes were estimated using a modified gradient approach. The highest NH3 mixing ratios (>30 nmol mol−1) occurred during early spring and late fall, coinciding with the timing of fertilizer application within the region and the occurrence of warm air temperatures. Net ecosystem NH3 exchange was greatest in spring and fall with peak emissions of about +50 nmol m−2 s−l. Annual NH3 emissions estimated using state-of-the-art inventories ranged from 0.6 to 1.4 × the mean annual gross tall tower fluxes (+2.1 nmol m−2 s−1). If the tall tower observations are representative of the Upper Midwest and broader U.S. Corn Belt regions, the annual gross emissions were +720 Gg NH3-N y−1 and +1,340 Gg NH3-N y−1, respectively. Finally, considering the N2O budget over the same region, we estimated total reactive N emissions (i.e., N2O + NH3) of approximately 1,790 Gg N y−1 from the U.S. Corn Belt, representing ~23% of the current annual new N input.
Bibliographical noteFunding Information:
This research was partially supported by the National Science Foundation (Grant 1640337), the United States Department of Agriculture National Institute of Food and Agriculture (USDA NIFA Grant 2018‐67019‐27808), USDA Agricultural Research Service, and the Minnesota Supercomputing Institute for Advanced Computational Research. JDW acknowledges support from the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research Program, through Oak Ridge National Laboratory's Terrestrial Ecosystem Science Science Focus Area; ORNL is managed by UT‐Battelle, LLC, for the U.S. DOE under contract DE‐AC05‐00OR22725. Finally, we acknowledge use of the National Atmospheric Deposition Program databases. The data presented in this manuscript are available at www.biometeorology.umn.edu/research/data‐archives and ESS‐DIVE (Deep Insights for Earth Science Data, https://ess‐dive.lbl.gov/ ).
- ammonia emissions
- emission inventories
- nitrous oxide
- reactive nitrogen
- regional fluxes
- tall tower