URBANA, Ill. – A team of researchers led by the University of Illinois Urbana-Champaign has developed a new method to quantify ammonia pollution across the United States in unprecedented detail. The new study published in Atmospheric Chemistry and Physics details the use of satellite observations to track where emissions are produced, how they change over time, and where they ultimately end up. The findings pinpoint several major agricultural ammonia hotspots across the country and reveal a 15-year rising trend in ammonia flux.
Agriculture is the primary source of atmospheric ammonia, which originates from both livestock operations and fertilizer use. Once in the atmosphere, it contributes to fine particulate air pollution, degrades ecosystems through nitrogen deposition, and can harm human health. Despite its importance, ammonia has been difficult to monitor because emissions vary dramatically across space and time, and ground-based measurements are sparse. The new work provides critical new insights into a largely overlooked but highly impactful form of air pollution tied closely to modern food production.
To address this gap, researchers combined more than a decade of satellite observations from two atmospheric sensors with a novel analytical method to estimate ammonia emissions and deposition across the contiguous United States. The approach allows scientists to move beyond simply observing atmospheric concentrations to directly estimating how much ammonia is being released and where it is being removed from the atmosphere.
The researchers identified five clear and consistent emission hotspots in major agricultural regions, including California’s San Joaquin Valley, the Snake River Valley in Idaho, the Texas Panhandle, the Great Plains, and parts of Pennsylvania and North Carolina. These regions are known for intensive livestock production and fertilizer use, and the satellite data confirms their major role in ammonia emissions.
Additionally, the study determined the fate of those ammonia emissions, revealing that much of it is deposited in nearby forests, grasslands, and wetlands, demonstrating that the gas is rapidly absorbed through deposition near its source rather than becoming chemically transformed higher in the atmosphere. This localized deposition can disrupt ecosystems by overloading them with nitrogen, contributing to soil acidification, water quality issues, and biodiversity loss. These seasonal and daily patterns could also help farmers fine-tune when they apply fertilizer, reducing how much nitrogen is lost to the atmosphere as ammonia.
Another key finding is the strong seasonal pattern in ammonia emissions. Emissions peak during warmer months, when higher temperatures increase volatilization from fertilizers and animal waste. In contrast, winter emissions are significantly lower. By combining data from satellites that pass over the Earth at different times of day, the study also captures previously unseen daily variations in emissions, offering a more complete picture of ammonia dynamics. Senior author Kaiyu Guan, the founding director of the Agroecosystem Sustainability Center and the Levenick Endowed Professor in Agroecosystem Modeling and Sensing, noted “This approach lets researchers move beyond simply estimating ammonia emissions to directly observing them, offering a clearer and more accurate picture than was previously possible.”
The study also highlights the advantages of satellite-based monitoring compared to traditional “bottom-up” emission inventories. While such inventories rely on reported agricultural activity and emission factors, satellite observations provide an independent, observation-based perspective that can capture fine-scale variability and reveal patterns that models may miss. “Satellite data allows us to see both the big picture and the local details,” explained the lead author Zitong Li, a PhD student under Guan’s supervision. “It complements existing approaches and helps reduce uncertainties in emission estimates.”
Importantly, the long-term record suggests that ammonia emissions may be increasing in several regions, likely driven by intensifying agricultural activity. These findings have important implications for environmental policy and air quality management. Because ammonia plays a key role in forming fine particulate pollution, reducing emissions could be a cost-effective strategy for improving air quality. At the same time, better understanding where and when emissions occur can help target mitigation efforts more effectively, particularly in agricultural systems.
As satellite technology and analytical methods continue to improve, researchers expect even more precise and timely monitoring of ammonia and other pollutants. This study represents a significant step toward integrating satellite data into routine environmental monitoring and decision-making. Ultimately, the work underscores the growing importance of combining advanced remote sensing with data-driven modeling to address complex environmental challenges and highlights the need for coordinated strategies to manage the impacts of modern agriculture on air quality and ecosystems.
The study titled “Ammonia emissions and depositions over the contiguous United States derived from IASI and CrIS using the directional derivative approach” is published in Atmospheric Chemistry and Physics (https://doi.org/10.5194/acp-26-703-2026), with support from NASA’s Interdisciplinary Science (IDS) program, USDA NIFA, and NSF.
For more information, contact:
Kaiyu Guan, Levenick Endowed Professor
Department of Natural Resources and Environmental Sciences
Founding Director, Agroecosystem Sustainability Center
University of Illinois Urbana-Champaign
kaiyug@illinois.edu