Satellite-detected ammonia changes in the United States: natural or anthropogenic impacts

Authors: HE, YAQIAN - University Of Central Arkansas; XU, RONGTING - Oregon State University; Prior, Stephen - Steve; YANG, DI - University Of Wyoming; YANG, ANNI - Colorado State University; CHEN, JIAN - Auburn University

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2021
Publication Date: 5/25/2021
Citation: He, Y., Xu, R., Prior, S.A., Yang, D., Yang, A., Chen, J. 2021. Satellite-detected ammonia changes in the United States: natural or anthropogenic impacts. Science of the Total Environment. 789:147899. https://doi.org/10.1016/j.scitotenv.2021.147899.
DOI: https://doi.org/10.1016/j.scitotenv.2021.147899

Interpretive Summary: Over the last century, the global N cycle has been heavily perturbed by additions of reactive N from human activities leading to increased atmospheric NH3. Synthetic N fertilizer application and livestock manure management are two dominant atmospheric NH3 sources that account for ~80% of total NH3 emission in the US. This modeling effort applied a satellite-based, 14-year monthly NH3 dataset to explore change in NH3 patterns and relationships with N fertilizer application, livestock manure production, and climate factors across the US. In addition to the US Midwest, the Mid-South and Western regions also experienced a striking increase in NH3 concentrations. Monthly atmospheric NH3 concentrations were positively correlated with monthly surface temperature in five US regions, with the highest found in the Mid-South. The influence of temperature on NH3 concentrations was highly related to N fertilizer use in the Northern Great Plains and that NH3 released from livestock manure during warmer winters contributed to increased NH3 in the Western US.. This new information will help policy-makers makers in developing mitigation strategies for agricultural NH3 emissions under future climate change scenarios.

Technical Abstract: Ammonia (NH3) is the most abundant alkaline component and can react with atmospheric acidic species to form aerosols that can lead to numerous environmental and health issues. Both satellite-based and in situ surface measurements depict obvious increases in atmospheric NH3 concentrations across the US in recent decades, with the highest rise detected in intensive agricultural regions. Previous studies have investigated underlying mechanisms of this considerable increase in the Midwestern US; however, detailed investigations of spatial and temporal changes in NH3 concentrations in remaining US regions are still lacking. Moreover, how atmospheric NH3 evolution is affected by changes in nitrogen (N) additions and interactions with climatic factors remains unknown. Herein we applied the Atmospheric Infrared Sounder (AIRS) monthly NH3 dataset to explore spatiotemporal pattern changes in atmospheric NH3 and the empirical relationships with synthetic N fertilizer application, livestock manure production, and climate factors across the entire US at both regional and pixel levels from 2002 to 2016. We found that, in addition to the US Midwest, the Mid-South and Western regions also experienced striking increases in NH3 concentrations. With a strong positive correlation between surface temperature and NH3 concentrations, these three regions could possibly become atmospheric NH3 hotspots in the context of future warming. The geographical and temporal weighted regression model (GTWR) revealed that the influence of temperature on temporal evolution of NH3 concentrations was highly correlated with synthetic N fertilizer use in the Midwest, with a positive effect in the Northern Great Plains and a weak effect in the eastern Midwest. Furthermore, our study suggested that NH3 released from livestock manure during warmer winters contributed to increased annual NH3 concentrations in the Western US. Our analyses provide an essential reference for US policy makers in developing mitigation strategies for agricultural NH3 emissions under future climate change scenarios.