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

Abstract

Nitrogen dioxide (NO₂) is a short-lived atmospheric pollutant that serves as an air qualityindicator and is itself a health concern. The Airborne Compact Atmospheric Mapper (ACAM) wasflown onboard the NASA UC-12 aircraft during the Deriving Information on Surface Conditions from Column andVertically Resolved Observations Relevant to Air Quality Marylandfield campaign in July 2011. The instrumentcollected hyperspectral remote sensing measurements in the 304–910 nm range, allowing daytimeobservations of several tropospheric pollutants, including nitrogen dioxide (NO₂), at an unprecedentedspatial resolution of 1.5 × 1.1 km ². Retrievals of slant column abundance are based on the differential opticalabsorption spectroscopy method. For the air mass factor computations needed to convert these retrievals tovertical column abundance, we include high-resolution information for the surface reflectivity by usingbidirectional reflectance distribution function data from the Moderate Resolution ImagingSpectroradiometer. We use high-resolution simulated vertical distributions of NO₂from the CommunityMultiscale Air Quality and Global Modeling Initiative models to account for the temporal variation inatmospheric NO₂to retrieve middle and lower tropospheric NO₂columns (NO₂below the aircraft). Wecompare NO₂derived from ACAM measurements with in situ observations from NASA’s P-3B researchaircraft, total column observations from the ground-based Pandora spectrometers, and tropospheric columnobservations from the space-based Ozone Monitoring Instrument. The high-resolution ACAM measurementsnot only give new insights into our understanding of atmospheric composition and chemistry throughobservation of subsampling variability in typical satellite and model resolutions, but they also provideopportunities for testing algorithm improvements for forthcoming geostationary air quality missions.