Abstract
Much concern has been raised about the increasing threat to air quality and human health due to ammonia (NH(3)) 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 NH(3) in the atmosphere, resulting in severe air and water pollution in this region. However, there is still a lack of accurate estimates of NH(3) emissions from agricultural systems. In this study, we simulated the agricultural NH(3) fluxes in SA by coupling the Bidirectional NH(3) exchange module (Bi-NH(3)) from the Community Multi-scale Air Quality model with the Dynamic Land Ecosystem Model. Our results indicated that NH(3) 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 NH(3) 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.