Nitrogen dioxide observations from the Geostationary Trace gas and Aerosol Sensor Optimization (GeoTASO) airborne instrument: retrieval algorithm and measurements during DISCOVER-AQ Texas 2013

Abstract

Abstract. The Geostationary Trace gas and Aerosol Sensor Optimization (GeoTASO) airborne instrument is a testbed for upcoming air quality satellite instruments that will measure backscattered ultraviolet, visible and near-infrared light from geostationary orbit. GeoTASO flew on the NASA Falcon aircraft in its first intensive field measurement campaign during the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) Earth Venture Mission over Houston, Texas in September 2013. Measurements of backscattered solar radiation between 420–465 nm collected on four days during the campaign are used to determine slant column amounts of NO2 at 250 m × 250 m spatial resolution with a fitting precision of 2.2 × 1015 molecules cm−2. These slant columns are converted to tropospheric NO2 vertical columns using a radiative transfer model and trace gas profiles from the Community Multiscale Air Quality (CMAQ) model. Total column NO2 from GeoTASO is well correlated with ground-based Pandora observations (r = 0.90 on the most polluted and cloud-free day of measurements), with GeoTASO NO2 slightly higher for the most polluted observations. Surface NO2 mixing ratios inferred from GeoTASO using the CMAQ model show good correlation with NO2 measured in situ at the surface during the campaign (r = 0.91 for the most polluted day). NO2 slant columns from GeoTASO also agree well with preliminary retrievals from the GEO-CAPE Airborne Simulator (GCAS) which flew on the NASA King Air B200 (r = 0.84, slope = 0.94). Enhanced NO2 is resolvable over areas of traffic NOx emissions and near individual petrochemical facilities.

High‐resolution NO2 observations from the Airborne Compact Atmospheric Mapper: Retrieval and validation

“…Previous studies on NO 2 vertical column retrievals from airborne spectrometers have relied on either geometric [e.g., Oetjen et al , ] or full radiative transfer (RT) AMF calculations [ Merlaud et al , ; Popp et al , ; Nowlan et al , ]. Here we explore how geometric AMFs relate to full RT AMFs and how their relationship changes with different observational, surface, and aerosol conditions.…”

“…In dedicated campaigns and related research activities, airborne remote sensing constitutes a valuable link between ground‐ and space‐based NO 2 observations, providing temporally and spatially resolved information [e.g., Kowalewski and Janz , ; Merlaud et al , ; Popp et al , ; Walter et al , ; Oetjen et al , ; Liu et al , ; Nowlan et al , ]. Airborne measurements can also serve as a test bed for both instrument design and retrieval algorithm development for future geostationary satellite instruments [e.g., Nowlan et al , ]. Retrieval algorithms that have been developed and tested for previous and current satellite instruments do not necessarily apply for geostationary observations taken over the entire day.…”

Tropospheric emissions: Monitoring of pollution (TEMPO)

“…Although neither GEMS nor Sentinel 4 will provide direct correlative data for TEMPO, maintaining close scientific ties with the scientists on these similar missions will foster consistent results in the constellation. For example, GeoTASO [81] airborne data and 10 Pandora ground stations will be used in the 2016 KORUS campaign for GEMS algorithm development and are also valuable potential validation data sources for TEMPO.…”

“…Based on spectra collected by GeoTASO [81], Hou et al [39] have developed a theoretical framework for multispectral retrieval of aerosol properties. GeoTASO is a test-bed instrument for TEMPO and was designed for analogous UV/Vis air quality measurements Information content analysis shows that in fine-mode aerosol dominated conditions (which are often the case over North America), the wavelength-dependent AOD and aerosol effective radius can be retrieved accurately [38].…”

“…To assist validation of this reflectance climatology and characterize reflectance of the land cover types at TEMPO resolutions, synchronous field and airborne data collection campaigns in the St Louis Metro region were performed. We have collected spectral reflectance data of various land cover types on the ground within hours of a GeoTASO [81] overpass using a field-based hyperspectral spectroradiometer and used GeoTASO data for spectral albedo measurements to develop a spectral albedo database of various land cover types found in Midwestern US.…”