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Validation of IASI NH3 columns at the single pixel scale from airborneand ground-based measurements

Abstract : Ammonia (NH3) is an important gas phase precursor species for aerosols, and ammoniated aerosols are significant components of unhealthy fine particulate matter and also exhibit a net cooling effect on climate. IASI column NH3 measurements provide global coverage at ~ 100 km2 (nadir) and sub daily resolution. However, validation of IASI NH3 measurements has been limited due to a lack of in-situ measurements. Because of the short atmospheric lifetime of NH3 (~ day), large spatiotemporal gradients further complicate NH3 IASI validations. To address these concerns, we have conducted a pixel scale validation of daytime (cloud coverage < 25%) IASI NH3 columns from surface-, vehicle-, radiosonde-, and aircraft-based measurements during the 2014 NASA DISCOVER-AQ and NSF FRAPPE field experiments in northeast Colorado, USA (July-August 2014). This region includes a diverse range of validation environments such as agricultural areas (Platte River Valley), urban emissions (Denver metropolitan area), and relativelyclean mountain and prairie regions. To minimize horizontal gradients, a narrow spatial window of ±15 km from the IASI centroid was used (corresponding to temporal window of ± 1 hour at the mean boundary layer wind speed of 4 m s-1). Due to the spiral flight tracks of the NASA P3-B aircraft, a majority of the vertical profiles extended from near the ground (1.5 km MSL) to 5.5 km above sea level, the typical flight ceiling of the P3-B aircraft in DISCOVER-AQ. NH3 concentrations above the flight ceiling were assumed to be zero, consistent with the IASI a prior profile. A total of 58 IASI/in-situ-derived columns were identified within these constraints. The mean relative error of IASI NH3 columns was 15% lower than those derived from the in-situ measurements. Given the in-situ measurement uncertainties (~25%), mean IASI error (38%) for these cases, and the strong spatial NH3 gradients observed in this area, the agreement between IASI and insitu measurement columns is excellent. No systematic bias is observed over IASI column abundances from 8x1014 to 4.4x1016 molec cm-2. These results present the first pixel scale validation for IASI NH3 and are at column abundances one order of magnitude lower than previous work with the NASA AURA TES NH3 columns. Ongoing efforts will examine validations at higher NH3 column abundances in areas such as the San Joaquin Valley (USA), explore the agreement at different spatiotemporal windows, and quantify the agreement with improved retrieval algorithms.
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Submitted on : Monday, April 25, 2016 - 5:56:56 PM
Last modification on : Thursday, June 4, 2020 - 10:24:07 AM


  • HAL Id : insu-01306900, version 1


Mark A. Zondlo, Lieven Clarisse, Martin van Damme, Simon Whitburn, Cathy Clerbaux, et al.. Validation of IASI NH3 columns at the single pixel scale from airborneand ground-based measurements. 4th IASI International Conference, Apr 2016, Antibes Juan-Les-Pins, France. ⟨insu-01306900⟩



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