Ammonium record over the last 96 years from the muztagata glacier in Central Asia

As a major alkaline gas in the atmosphere, ammonia (NH₃) plays an important role in atmospheric chemistry. However, there is little knowledge about NH₃ variations in the Central Asia. Here we analyzed the ammonium (NH₄⁺) history recorded in an ice core from the East Pamir in Central Asia, which was drilled on the Mt. Muztagata at the elevation of 7010 m a.s.l. in 2003. The core was carefully dated and NH₄⁺ concentration history during 1907–2002 was reconstructed. The result shows that NH₄⁺ concentration remained approximately constant until the 1930s after a sudden decrease at the very beginning of the 20th century, followed by a minimum in 1940 before increasing steadily to the peak at the end of 1990s. It is found that the annual mean NH₄⁺ concentration was strongly associated with the Northern Hemisphere temperature, suggesting the impact of temperature on NH₃ emissions in the Central Asia. Moreover, an increase of NH₄⁺ concentration after 1940 also reflects the enhancement of NH₃ emissions from anthropogenic sources such as fertilizer applications and livestock wastes in the 20th century. Supported by the National Basic Research Program of China (Grant No. 2005CB422004) and the National Natural Science Foundation of China (Grant Nos. 40121101, 40571039 and 40471022)