TES ammonia retrieval strategy and global observations of the spatial and seasonal variability of ammonia

Abstract

Abstract. Presently only limited sets of tropospheric ammonia (NH 3 ) measurements in the Earth's atmosphere have been reported from satellite and surface station measurements, despite the well-documented negative impact of NH 3 on the environment and human health. Presented here is a detailed description of the satellite retrieval strategy and analysis for the Tropospheric Emission Spectrometer (TES) using simulations and measurements. These results show that: (i) the level of detectability for a representative boundary layer TES NH 3 mixing ratio value is ∼0.4 ppbv, which typically corresponds to a profile that contains a maximum level value of ∼1 ppbv; (ii) TES NH 3 retrievals generally provide at most one degree of freedom for signal (DOFS), with peak sensitivity between 700 and 900 mbar; (iii) TES NH 3 retrievals show significant spatial and seasonal variability of NH 3 globally; (iv) initial comparisons of TES observations with GEOS-CHEM estimates show TES values being higher overall. Important differences and similarities between modeled and observed seasonal and spatial trends are noted, with discrepancies indicating areas where the timing and magnitude of modeled NH 3 emissions from agricultural sources, and to lesser extent biomass burning sources, need further study.

Characterization of Aura TES carbonyl sulfide retrievals over ocean

“…In this paper, we only report the retrievals over ocean. We do not take into account the impact of aerosols on OCS retrievals since the spectral region we use is from the mid-infrared region and aerosols from biomass burning negligibly affect the retrievals (Shephard et al, 2011;Verma et al, 2009;Worden et al, 2013). Although significant dust from the desert could affect mid-IR (infrared) retrievals, the current study is limited to over the Pacific and aerosols there are mostly from biomass burning.…”

Simulation of nitrate, sulfate, and ammonium aerosols over the United States

“…To investigate the extent to which California ammonia emissions might be underestimated in GEOS-Chem, model predictions are compared to satellite measurements of ammonia in California in 2009 from the Tropospheric Emissions Spectrometer (TES) (Shephard et al, 2011;Beer et al, 2008). TES is a high-resolution (0.06 cm −1 ) Fourier transform spectrometer onboard NASA's Aura satellite, in a sun-synchronous orbit with measurements at 01:30 and 13:30 LT.…”

“…Only TES retrievals with sufficiently high sensitivity (degrees of freedom for signal ≥ 0.5) are included in the comparison, with a total of 142 retrievals over the year. Inherent in our comparison is a mismatch in scales, since the TES footprint is approximately 5 × 8 km (Shephard et al, 2011), compared with the GEOS-Chem grid box size of approximately 56 × 60 km in California. However, since the predominant sources of ammonia in California are agricultural sources emitting over extended areas, we expect that sub-grid scale variations will be relatively small.…”

“…To reduce the influence of the a priori profiles in the comparison of GEOS-Chem predictions with TES, representative volume mixing ratio (RVMR) values (Shephard et al, 2011) are compared for the retrieved profiles from TES and GEOS-Chem. The RVMR is a boundary layer average volume mixing ratio (VMR) which is weighted by the TES sensitivity to provide an ammonia concentration that is representative of the vertical region over which TES is most sensitive.…”

Validation of the CrIS fast physical NH<sub>3</sub> retrieval with ground-based FTIR

“…Over the last decade the development of satellite observations of NH 3 from instruments such as the Cross-track Infrared Sounder (CrIS, , the Infrared Atmospheric Sounding Interferometer (IASI, Clarisse et al, 2009;Coheur et al, 2009;Van Damme et al, 2014a), the Atmospheric Infrared Sounder (AIRS, Warner et al, 2016) and the Tropospheric Emission Spectrometer (TES, Beer et al, 2008;Shephard et al, 2011) have shown the potential to improve our understanding of NH 3 distribution. Recent studies show the global distribution of NH 3 measured at a twice daily scale (Van Damme et al, 2014a, 2015a can reveal seasonal cycles and distributions for regions where measurements were unavailable until now.…”