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 test bed 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 and 465 nm collected on 4 days during the campaign are used to determine slant column amounts of NO 2 at 250 m × 250 m spatial resolution with a fitting precision of 2.2 × 10 15 molecules cm −2 . These slant columns are converted to tropospheric NO 2 vertical columns using a radiative transfer model and trace gas profiles from the Community Multiscale Air Quality (CMAQ) model. Total column NO 2 from GeoTASO is well correlated with ground-based Pandora observations (r = 0.90 on the most polluted and cloud-free day of measurements and r = 0.74 overall), with GeoTASO NO 2 slightly higher for the most polluted observations. Surface NO 2 mixing ratios inferred from GeoTASO using the CMAQ model show good correlation with NO 2 measured in situ at the surface during the campaign (r = 0.85). NO 2 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 = 0.81, slope = 0.91). Enhanced NO 2 is resolvable over areas of traffic NO x emissions and near individual petrochemical facilities.

The Dawn of Geostationary Air Quality Monitoring: Case Studies From Seoul and Los Angeles

“…As a result, observations at Yonsei University are biased low at all times of the day, especially in the morning hours, when the unsampled portion of the boundary layer (130 m) is a larger component of the typically shallower NO 2 mixing depth. A similar bias has been observed and quantified for previous Pandora measurements in Houston using coincident NO 2 in situ measurements (Judd, 2016;Nowlan et al, 2016), however this potential bias does not change the larger conclusions made here.…”

“…These measurements are total NO 2 column with no differentiation of stratospheric or tropospheric NO 2 contributions, but as discussed in section GeoTASO, stratospheric contributions are relatively small and uniform over the SMA and the LA Basin. Data from these instruments have been used to assess spaceand aircraft-based retrievals of NO 2 columns (Flynn et al, 2014;Nowlan et al, 2016;Goldberg et al, 2017), as well as to study the spatiotemporal variability of trace gases in urban environments (Tzortziou et al, 2015) and column-to-surface relationships and their relation to boundary layer depth (Flynn et al, 2014;Knepp et al, 2015). Further understanding the effects of boundary layer depth on air quality has been identified as a "most important" objective by the National Academy of Sciences' most recent Decadal Survey (2017-2027) (National Academies of Sciences Engineering Medicine, 2018).…”

“…Though the TDSC does not provide the absolute magnitude of the NO 2 column, it does provide a very good approximation for the difference in column density relative to the background represented in each region's reference spectrum. Data from GeoTASO NO 2 vertical column retrievals from the deployment in Houston, Texas in 2013 were used to assess the TDSC approximation (Nowlan et al, 2016; available at https://www-air.larc.nasa.gov/missions/discover-aq/discoveraq.html). A multiple-variable linear regression of the Houston dataset shows that 94% of the variation in vertical column is driven by the TDSC (linear coefficient of 0.85 ± 0.0002).…”

“…To begin addressing the spatial and temporal challenges associated with GEO measurements prior to launch, NASA funded the development of the suborbital Geostationary Trace gas and Aerosol Sensor Optimization instrument (GeoTASO, Leitch et al, 2014;Nowlan et al, 2016) and has deployed it during recent field experiments that also included networks of ground-based UV-VIS solar spectrometers (Herman et al, 2009Pandora). Analogous to how the LEO observations are a transfer standard between the GEO domains, the airborne observations are a transfer standard between the spatial scales of the surface-based validation instruments (i.e., Pandora) and satellite observations.…”

The Small Whiskbroom Imager for atmospheric compositioN monitorinG (SWING) and its operations from an unmanned aerial vehicle (UAV) during the AROMAT campaign

“…Those operating in the UV-visible range often use the differential optical absorption spectroscopy (DOAS) method (Platt and Stutz, 2008). Early airborne DOAS studies were based on zenithonly measurements from aircraft to quantify the stratospheric NO 2 and O 3 at high latitudes (Wahner et al, 1989;Pfeilsticker and Platt, 1994). The technique was then modified, adding nadir and off-axis angles (e.g.…”