Ground-based direct-sun DOAS and airborne MAX-DOAS measurements of the collision-induced oxygen complex, O.sub.2O.sub.2, absorption with significant pressure and temperature differences

• Published in: Atmospheric measurement techniques 2015-02, Vol.8 (2), p.793
• Main Authors: Spinei, E, Cede, A, Herman, J, Mount, G. H, Eloranta, E, Morley, B, Baidar, S, Dix, B, Ortega, I, Koenig, T, Volkamer, R
• Format: Article
• Language: English
• Subjects: Analysis; Measurement; Remote sensing
• ISSN: 1867-1381; 1867-8548

The collision-induced O.sub.2 complex, O.sub.2 O.sub.2, is a very important trace gas for understanding remote sensing measurements of aerosols, cloud properties and atmospheric trace gases. Many ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of the O.sub.2 O.sub.2 optical depth require correction factors of 0.75 ± 0.1 to reproduce radiative transfer modeling (RTM) results for a nearly pure Rayleigh atmosphere. One of the potential causes of this discrepancy is uncertainty in laboratory-measured O.sub.2 O.sub.2 absorption cross section temperature and pressure dependencies due to difficulties in replicating atmospheric conditions in the laboratory environment. This paper presents ground-based direct-sun (DS) and airborne multi-axis (AMAX) DOAS measurements of O.sub.2 O.sub.2 absorption optical depths under actual atmospheric conditions in two wavelength regions (335-390 and 435-490 nm). DS irradiance measurements were made by the Washington State University research-grade Multi-Function Differential Spectroscopy Instrument instrument from 2007 to 2014 at seven sites with significant pressure (778 to 1013 hPa) and O.sub.2 O.sub.2 profile-weighted temperature (247 to 275 K) differences. Aircraft MAX-DOAS measurements were conducted by the University of Colorado (CU) AMAX-DOAS instrument on 29 January 2012 over the Southern Hemispheric subtropical Pacific Ocean. Scattered solar radiance spectra were collected at altitudes between 9 and 13.2 km, with O.sub.2 O.sub.2 profile-weighted temperatures of 231 to 244 K and nearly pure Rayleigh scattering conditions. Due to the well-defined DS air-mass factors during ground-based measurements and extensively characterized atmospheric conditions during the aircraft AMAX-DOAS measurements, O.sub.2 O.sub.2 "pseudo" absorption cross sections, σ, are derived from the observed optical depths and estimated O.sub.2 O.sub.2 column densities. Vertical O.sub.2 O.sub.2 columns are calculated from the atmospheric sounding temperature, pressure and specific humidity profiles. Based on the ground-based atmospheric DS observations, there is no pressure dependence of the O.sub.2 O.sub.2 σ within the measurement errors (3%). Two data sets are combined to derive the peak σ temperature dependence of the 360 and 477 nm dimer absorption bands from 231 to 275 K. DS and AMAX-derived peak σ ( O.sub.2 O.sub.2) as a function of T can be described by a quadratic function at 360 nm and linear func