Half-Century Ammonia Emissions From Agricultural Systems in Southern Asia: Magnitude, Spatiotemporal Patterns, and...

Much concern has been raised about the increasing threat to air quality and human health due to ammonia (NH₃) emissions from agricultural systems, which is associated with the enrichment of reactive nitrogen (N) in southern Asia (SA), home of more than 60% the world's population (i.e., the people of West, central, East, South, and Southeast Asia). Southern Asia consumed more than half of the global synthetic N fertilizer and was the dominant region for livestock waste production since 2004. Excessive N application could lead to a rapid increase of NH₃ in the atmosphere, resulting in severe air and water pollution in this region. However, there is still a lack of accurate estimates of NH₃ emissions from agricultural systems. In this study, we simulated the agricultural NH₃ fluxes in SA by coupling the Bidirectional NH₃ exchange module (Bi-NH₃) from the Community Multi-scale Air Quality model with the Dynamic Land Ecosystem Model. Our results indicated that NH₃ emissions were 21.3 ± 3.9 Tg N yr^-1 from SA agricultural systems with a rapidly increasing rate of ~0.3 Tg N yr^-2 during 1961-2014. Among the emission sources, 10.8 Tg N yr^-1 was released from synthetic N fertilizer use, and 10.4 ± 3.9 Tg N yr^-1 was released from manure production in 2014. Ammonia emissions from China and India together accounted for 64% of the total amount in SA during 2000-2014. Our results imply that the increased NH₃ emissions associated with high N inputs to croplands would likely be a significant threat to the environment and human health unless mitigation efforts are applied to reduce these emissions.