Nitrogen dioxide and formaldehyde measurements from the GEOstationary Coastal and Air Pollution Events (GEO-CAPE) Airborne Simulator over Houston, Texas

Abstract

The GEOstationary Coastal and Air Pollution Events (GEO-CAPE) Airborne Simulator (GCAS) was developed in support of NASA's decadal survey GEO-CAPE geostationary satellite mission. GCAS is an airborne push-broom remote-sensing instrument, consisting of two channels which make hyperspectral measurements in the ultraviolet/visible (optimized for air quality observations) and the visible–near infrared (optimized for ocean color observations). The GCAS instrument participated in its first intensive field campaign during the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) campaign in Texas in September 2013. During this campaign, the instrument flew on a King Air B-200 aircraft during 21 flights on 11 days to make air quality observations over Houston, Texas. We present GCAS trace gas retrievals of nitrogen dioxide (NO₂) and formaldehyde (CH₂O), and compare these results with trace gas columns derived from coincident in situ profile measurements of NO₂ and CH₂O made by instruments on a P-3B aircraft, and with NO₂ observations from ground-based Pandora spectrometers operating in direct-sun and scattered light modes. GCAS tropospheric column measurements correlate well spatially and temporally with columns estimated from the P-3B measurements for both NO₂ (r²=0.89) and CH₂O (r²=0.54) and with Pandora direct-sun (r²=0.85) and scattered light (r²=0.94) observed NO₂ columns. Coincident GCAS columns agree in magnitude with NO₂ and CH₂O P-3B-observed columns to within 10 % but are larger than scattered light Pandora tropospheric NO₂ columns by 33 % and direct-sun Pandora NO₂ columns by 50 %.