Tracking elevated pollution layers with a newly developed hyperspectral Sun/Sky spectrometer (4STAR): Results from the TCAP 2012 and 2013 campaigns

Abstract

Total columnar water vapor (CWV), nitrogen dioxide (NO₂), and ozone (O₃)arederivedfromanewly developed, hyperspectral airborne Sun-sky spectrometer (4STAR) for thefirst time during the twointensive phases of the Two-Column Aerosol Project (TCAP) in summer 2012 and winter 2013 aboard the DOEG-1 aircraft. We compare results with coincident measurements. Wefind 0.045 g/cm²(4.2%) negative bias and0.28g/cm²(26.3%) root-mean-square difference (RMSD) in water vapor layer comparison with an in situhygrometer and an overall RMSD of 1.28 g/m³(38%) water vapor amount in profile by profile comparisons, withdifferences distributed evenly around zero. RMSD for O₃columns average to 3%, with a 1% negative bias for4STAR compared with the Ozone Measuring Instrument along aircraftflight tracks for 14flights during bothTCAP phases. Ground-based comparisons with Pandora spectrometers at the Goddard Space Flight Center,Greenbelt, Maryland, showed excellent agreement between the instruments for both O₃(1% RMSD and 0.1%bias) and NO₂(17.5% RMSD and 8% bias). We apply clustering analysis of the retrieved products as a casestudy during the TCAP summer campaign to identify variations in atmospheric composition of elevated pollutionlayers and demonstrate that combined total column measurements of trace gas and aerosols can be used todefine different pollution layer sources, by comparing our results with trajectory analysis and in situ airborneminiSPLAT (single-particle mass spectrometer) measurements. Our analysis represents afirst step in linkingsparse but intense in situ measurements from suborbital campaigns with total column observations from space