Cross-track Infrared Sounder (CrIS) satellite observations of tropospheric ammonia

[摘要] Observations of atmospheric ammonia are important in understanding andmodelling the impact of ammonia on both human health and the naturalenvironment. We presenta detailed description of a robust retrievalalgorithm that demonstrates the capabilities of utilizing Cross-trackInfrared Sounder (CrIS) satellite observations to globally retrieval ammoniaconcentrations. Initial ammonia retrieval results using both simulated andreal observations show that (i) CrIS is sensitive to ammonia in theboundary layer with peak vertical sensitivity typically around~ 850–750 hPa (~ 1.5 to 2.5 km), which can dipdown close to the surface (~ 900 hPa) under ideal conditions,(ii) it has a minimum detection limit of ~ 1 ppbv (peak profilevalue typically at the surface), and (iii) the information content can varysignificantly with maximum values of ~ 1 degree-of-freedomfor signal. Comparisons of the retrieval with simulated "true" profilesshow a small positive retrieval bias of 6% with a standard deviation of~ ± 20% (ranging from ± 12 to ±30% over the vertical profile). Note that these uncertainty estimates areconsidered as lower bound values as no potential systematic errors areincluded in the simulations. The CrIS NH₃ retrieval applied over theCentral Valley in CA, USA, demonstrates that CrIS correlates well with thespatial variability of the boundary layer ammonia concentrations seen by thenearby Quantum Cascade-Laser (QCL) in situ surface and the TroposphericEmission Spectrometer (TES) satellite observations as part of theDISCOVER-AQ campaign. The CrIS and TES ammonia observations showquantitatively similar retrieved boundary layer values that are often withinthe uncertainty of the two observations. Also demonstrated is CrIS's abilityto capture the expected spatial distribution in the ammonia concentrations,from elevated values in the Central Valley from anthropogenic agricultureemissions, to much lower values in the unpolluted or clean surroundingmountainous regions. These initial results demonstrate the capabilities ofthe CrIS satellite to measure ammonia.

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