Tall tower ammonia observations and emission estimates in the U.S. Midwest

Authors: GRIFFIS, TIMOTHY - University Of Minnesota; HU, CHENG - University Of Minnesota; Baker, John; WOOD, JEFFREY - University Of Minnesota; MILLET, DYLAN - University Of Minnesota; ERICKSON, MATTHEW - University Of Minnesota; YU, ZHONGJIE - University Of Minnesota; DEVENTER, JULIAN - University Of Minnesota; Winker, Cody; CHEN, ZICHONG - University Of Minnesota

Submitted to: Journal of Geophysical Research-Biogeosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2019
Publication Date: 10/10/2019
Citation: Griffis, T.J., Hu, C., Baker, J.M., Wood, J.D., Millet, D.B., Erickson, M.D., Yu, Z., Deventer, J.M., Winker, C.D., Chen, Z. 2019. Tall tower ammonia observations and emission estimates in the U.S. Midwest. Journal of Geophysical Research-Biogeosciences. 124(11):3432-3447. https://doi.org/10.1029/2019JG005172.
DOI: https://doi.org/10.1029/2019JG005172

Interpretive Summary: Ammonia (NH3) is a chemical of concern in the atmosphere because it reacts readily with acid to produce fine particulate matter that has been linked to human health concerns that are estimated to cost the US nearly $36 billion annually. Atmospheric concentrations have increased dramatically due to the massive increase in the use of nitrogen fertilzer over the past 70 years. The development of regulations to reduce atmospheric NH3 has been hampered by a poor understanding of the distribution of sources, both spatially and temporally due to measurement difficulties. We have attempted to address this problem by deploying an ammonia analyzer at the University of Minnesota tall tower trace gas observatory near Rosemount MN. Measurements were conducted ontinuously over the period from April 2017 to December 2018 at 100 m and 56 m above the ground, providing regional estimates of net ecosystem NH3 exchange. If the measured emissions are considered representative of the US Corn Belt, we estimate gross emissions of 1275 Gg NH3-N per year. Combining that with our earlier estimates for N2O, we estimate that total reactive N emission to the atmosphere (NH3 + N2O)is about 1750 Gg per year, or 23% of the total amount of N applied as fertilizer in the region.These data will be useful in assessing the magnitude of the problem, and in developong corrective measures.

Technical Abstract: Atmospheric ammonia (NH3) has increased dramatically as a consequence of the production of 40 synthetic nitrogen (N) fertilizer and proliferation of livestock. 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 from within the US Corn Belt for the period April 2017 to December 2018. Hourly average NH3 mixing ratios were measured at 100 m and 56 m above the ground surface and fluxes were estimated using a modified gradient approach. The largest NH3 mixing ratios (>30 nmol mol-1) were observed during early spring and late fall, corresponding 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 1.5 x _the mean annual gross tall tower flux densities (+2.0 nmol m-2 s-1). If the tall tower observations are representative of the Upper Midwest and broader US Corn Belt regions, the annual gross emissions are +685 Gg NH3-N y-1 and +1275 Gg NH3-N y-1, respectively. By also considering the N2O budget over the same region, we estimated a total reactive N emission (i.e. N2O + NH3) of approximately 1750 Gg N y-1 from the US Corn Belt, representing ~23% of the current annual synthetic N input.