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

Mark A. Zondlo (1) , Lieven Clarisse (2) , Martin van Damme (2) , Simon Whitburn (2) , Cathy Clerbaux (3, 2) , Pierre-François Coheur (2)

1 Princeton University
2 Spectroscopie de l'atmosphère, Service de Chimie Quantique et Photophysique
3 TROPO - LATMOS

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.

Domains: Atmospheric and Oceanic Physics [physics.ao-ph]; Environmental Sciences

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⟩