The Geostationary Trace gas and Aerosol Sensor Optimization (GeoTASO) airborne instrument is a test-bed for the satellite instruments mentioned above. It measures backscattered radiance with a spectrometer covering the spectral range between 290–695 nm. GeoTASO onboard B-200 (UC-12B) – LARC aircraft flew over the Korean Peninsula with the spatial resolution of 250 m x 250 m, during the Korea-United States Air Quality (KORUS-AQ) campaign from May to June 2016. Because of the similarities between characteristics of the upcoming GEMS and the GeoTASO instruments, measurements from GeoTASO in Korea can be employed for preparation of algorithms for GEMS trace gas retrievals.
Principal component analysis (PCA) technique was used to retrieve slant column densities (SCDs) of sulfur dioxide (SO2), nitrogen dioxide (NO2), and formaldehyde (HCHO). The fitting windows we used for SO2, NO2, and HCHO retrievals are 310–325 nm, 423–451 nm and 328.5–356.5 nm, respectively. The principal components (PCs) of each species were collected from relatively clean areas on the flight paths where are expected to have less SCDs than other areas. SCDs of each trace gas were obtained by fitting the PCs extracted from each cross-track of GeoTASO and the absorption cross section of each species to measured radiance. To convert the obtained SCDs to vertical column densities (VCDs), air mass factors (AMFs) of each species were calculated using atmospheric profiles from chemical transport model outputs. The VCDs of each species well capture point sources on the flight paths and their plumes propagating downwind areas. The retrieved column amounts were compared and/or validated against other measurements, including trace gas amounts retrieved from other GeoTASO algorithms, and ground-based measurements during the campaign.