Abstract
Abstract. Multi-axis differential optical absorption spectroscopy (MAX-DOAS) is a widely used measurement technique for the detection of a variety of atmospheric trace gases. Using inverse modelling, the observation of trace gas column densities along different lines of sight enables the retrieval of aerosol and trace gas vertical profiles in the atmospheric boundary layer using appropriate retrieval algorithms. In this study, the ability of eight profile retrieval algorithms to reconstruct vertical profiles is assessed on the basis of synthetic measurements. Five of the algorithms are based on the optimal estimation method, two on parametrised approaches, and one using an analytical approach without involving any radiative transfer modelling. The synthetic measurements consist of the median of simulated slant column densities of O4 at 360 and 477 nm, as well as of HCHO at 343 nm and NO2 at 477 nm, from seven datasets simulated by five different radiative transfer models. Simulations are performed for a combination of 10 trace gas and 11 aerosol profiles, as well as 11 elevation angles, three solar zenith, and three relative azimuth angles. Overall, the results from the different algorithms show moderate to good performance for the retrieval of vertical profiles, surface concentrations, and total columns. Except for some outliers, the root-mean-square difference between the true and retrieved state ranges between (0.05–0.1) km−1 for aerosol extinction and (2.5–5.0) ×1010 molec cm−3 for HCHO and NO2 concentrations.
Highlights
The planetary boundary layer (PBL) is the part of the atmosphere that is in direct contact with the terrestrial biosphere
A versatile tool for the monitoring of atmospheric trace gases and aerosol content of the PBL is the well-known multi-axis differential optical absorption spectroscopy (MAX-DOAS) (e.g. Hönninger et al, 2004; Wagner et al, 2004; Heckel et al, 2005; Frieß et al, 2006; Platt and Stutz, 2008; Irie et al, 2008; Clémer et al, 2010; Wagner et al, 2011; Vlemmix et al, 2015b). It relies on the spectral analysis of scattered sunlight and enables the simultaneous detection of numerous trace gases, such as nitrogen dioxide (NO2), formaldehyde (HCHO), nitrous acid (HONO), water vapour (H2O), sulfur dioxide (SO2), ozone (O3), and halogen oxides
This paper presents the first intercomparison of eight state-of-the-art algorithms for the retrieval of vertical profiles of aerosols and trace gases using synthetic MAX-DOAS measurements
Summary
The planetary boundary layer (PBL) is the part of the atmosphere that is in direct contact with the terrestrial biosphere. Its chemical composition is determined by anthropogenic and natural emissions Monitoring of both chemical composition and aerosol content of the PBL is crucial for the understanding of the chemical and physical processes and the spatio-temporal evolution of PBL composition. Hönninger et al, 2004; Wagner et al, 2004; Heckel et al, 2005; Frieß et al, 2006; Platt and Stutz, 2008; Irie et al, 2008; Clémer et al, 2010; Wagner et al, 2011; Vlemmix et al, 2015b) It relies on the spectral analysis of scattered sunlight and enables the simultaneous detection of numerous trace gases, such as nitrogen dioxide (NO2), formaldehyde (HCHO), nitrous acid (HONO), water vapour (H2O), sulfur dioxide (SO2), ozone (O3), and halogen oxides.
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