The Mainz profile algorithm (MAPA)

Steffen Beirle,Thomas Wagner,Sebastian Donner,Steffen Dörner,Yang Wang,Julia Remmers

doi:10.5194/amt-12-1785-2019

Steffen Beirle, Thomas Wagner + Show 4 more

Open Access

https://doi.org/10.5194/amt-12-1785-2019

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Abstract

Abstract. The Mainz profile algorithm (MAPA) derives vertical profiles of aerosol extinction and trace gas concentrations from MAX-DOAS measurements of slant column densities under multiple elevation angles. This paper presents (a) a detailed description of the MAPA (v0.98), (b) results for the CINDI-2 campaign, and (c) sensitivity studies on the impact of a priori assumptions such as flag thresholds. Like previous profile retrieval schemes developed at MPIC, MAPA is based on a profile parameterization combining box profiles, which also might be lifted, and exponential profiles. But in contrast to previous inversion schemes based on least-square fits, MAPA follows a Monte Carlo approach for deriving those profile parameters yielding best match to the MAX-DOAS observations. This is much faster and directly provides physically meaningful distributions of profile parameters. In addition, MAPA includes an elaborated flagging scheme for the identification of questionable or dubious results. The AODs derived with MAPA for the CINDI-2 campaign show good agreement with AERONET if a scaling factor of 0.8 is applied for O4, and the respective NO2 and HCHO surface mixing ratios match those derived from coincident long-path DOAS measurements. MAPA results are robust with respect to modifications of the a priori MAPA settings within plausible limits.

Highlights

We present Mainz profile algorithm (MAPA) results exemplarily for differential slant column density (dSCD) sequences of O4, NO2, and HCHO measured during the Second Cabauw Intercomparison of Nitrogen Dioxide Measuring Instruments (CINDI-2) during September 2016 (Kreher et al, 2019)
We focus on two days, 15 and 23 September, which are mostly cloud free and have been selected as reference days within CINDI-2 intercomparisons (Tirpitz et al, 2019)
O4 dSCDs have been analyzed according to the DOAS settings specified in Table A3 in Kreher et al (2019) but with sequential instead of noon reference spectra

Summary

Introduction

Multi-axis differential optical absorption spectroscopy (MAX-DOAS), i.e., spectral measurements of scattered sunlight under different viewing elevation angles, has become a useful tool for the determination of vertical profiles of aerosols and various trace gases within the lower troposphere (e.g., Hönninger and Platt, 2002; Hönninger et al, 2004; Wagner et al, 2004; Wittrock et al, 2004; Frieß et al, 2006; Clémer et al, 2010), which is key for the validation of trace gas columns derived from satellite measurements. MAX-DOAS is based on the elevation angle dependency of spectral absorption, i.e., the differential slant column density (dSCD) determined by DOAS (Platt and Stutz, 2008). The “profile inversion” consists of inverting this forward model, i.e., finding the extinction and concentration profile where forward modeled and measured dSCD elevation sequences agree

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