September 1, 2016
Increased Atmospheric Ammonia over the World’s Major Agricultural Areas Detected from Space
AOSC, University of Maryland
Atmospheric ammonia (NH3), an important component of the global nitrogen cycle, impacts climate, acidification and eutrophication of ecosystems, and the formation of ammonium-containing aerosols. Through recent improvements in retrieval algorithms, the Atmospheric Infrared Sounder (AIRS) aboard NASA's Aqua satellite now provides daily global measurements of atmospheric NH3 with peak sensitivity at an altitude about 800 m above sea level. This study provides a first, quantitative analysis of recent (2002 – 2015) trends in NH3 concentrations on a global scale. Although forest fires and other biomass burning contribute to atmospheric ammonia, the main sources are agricultural activities (farming and animal husbandry) involving reactive nitrogen ultimately derived from fertilizer use; rates of emission are also sensitive to climate change. Substantial increases are seen over the US (3.43 ± 0.16% yr-1), the European Union (2.31 ± 0.16% yr-1), and China (2.78 ± 0.15% yr-1). Over the EU, the trend results from decreased scavenging by acid aerosols. Over the US, the increase results primarily from a combination of decreased scavenging and increased temperatures. Over China, the increase results primarily from increased fertilizer and decreased SO2 emissions. Over South Asia, increased NH3 emissions are apparently masked by increased SO2 and NOx emissions, leading to increased aerosol loading and adverse health effects.