Global estimates of dry ammonia deposition inferred from space-measurements.

Ammonia (NH 3), as an alkaline gas, contributes substantially to atmospheric nitrogen deposition, which can cause biodiversity loss, water eutrophication and soil acidification. Advances in the application of satellite observations allow us to gain deeper insights into atmospheric NH 3 concentrations at large spatial scales. A new satellite-based methodology is proposed for estimating dry NH 3 deposition with consideration of bi-directional NH 3 exchange. We estimate the global dry NH 3 deposition for nine years (2008–2016) by using the Infrared Atmospheric Sounding Interferometer Instrument (IASI) NH 3 retrievals. Satellite-based dry NH 3 deposition is in general consistent with measured dry NH 3 deposition over the monitoring sites (R2 = 0.65). Global dry NH 3 deposition over 8 kg N ha−1 is mainly distributed in the Eastern China, Northern and Central Pakistan, and Northern India. An annual increase rate of 0.27 and 0.13 kg N ha−1 y−1 in dry NH 3 deposition during 2008–2016 occurs in Eastern China and Sichuan Basin, which are the major Chinese agricultural regions. The NH 3 compensation point is high during warm months, and can be above 1 μg m−3 such as in Eastern China, implying the importance of considering the NH 3 compensation points for estimating dry NH 3 deposition. We find, if the upward NH 3 flux was ignored, it will cause 11%, 17%, 5% and 3% overestimation in dry NH 3 deposition in Eastern China, Northern India, Eastern United States and Western Europe, respectively. This study presents the potential of using the satellite retrievals to estimate the large-scale dry NH 3 deposition, and the methodology is able to provide temporally continuous and spatially complete fine-resolution datasets. Unlabelled Image • A new satellite-based method is proposed to estimate dry ammonia deposition. • An overestimation in dry ammonia deposition will be caused using unidirectional methods. • Satellite-based estimates capture the general variability of dry ammonia deposition. [ABSTRACT FROM AUTHOR]