Atmospheric ammonia retrieval from the TANSO-FTS/GOSAT thermal infrared sounder
Abstract. Hyperspectral thermal infrared sounders enable us to grasp the global
behavior of minor atmospheric constituents. Ammonia, which imparts large
impacts on the atmospheric environment by reacting with other species, is one
of them. In this work, we present an ammonia retrieval system that we
developed for the Greenhouse Gases Observing Satellite (GOSAT) and the
estimates of global atmospheric ammonia column amounts that we derived from
2009 to 2014. The horizontal distributions of the seasonal ammonia column
amounts represent significantly high values stemming from six anthropogenic
emission source areas and four biomass burning ones. The monthly mean time
series of these sites were investigated, and their seasonality was clearly
revealed. A comparison with the Infrared Atmospheric Sounding Interferometer
(IASI) ammonia product showed good agreement spatially and seasonally, though
there are some differences in detail. The values from GOSAT tend to be
slightly larger than those from IASI for low concentrations, especially in
spring and summer. On the other hand, they are lower for particularly high
concentrations during summer, such as eastern China and northern India. In
addition, the largest differences were observed in central Africa. These
differences seem to stem from the temporal gaps in observations and the
fundamental differences in the retrieval systems.