Half-Century Ammonia Emissions From Agricultural Systems in Southern Asia: Magnitude, Spatiotemporal Patterns, and Implications for Human Health

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 21.33.9TgNyr(-1) from SA agricultural systems with a rapidly increasing rate of similar to 0.3TgNyr(-2) during 1961-2014. Among the emission sources, 10.8TgNyr(-1) was released from synthetic N fertilizer use, and 10.43.9TgNyr(-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. Plain Language Summary Farming practices in southern Asia (SA), including synthetic fertilizer and manure application, have resulted in the emission of tremendous amounts of ammonia, an atmospheric constituent that has been linked to human respiratory and cardiovascular ailments and also to atmospheric haze. Ammonia emission is expected to increase due to population growth and increased demand for animal products. Ammonia emission is a critically important environmental issue that needs to be addressed collaboratively by farmers and policymakers in the SA region.