The tilt-effect in DOAS observations

Lampel, Johannes; Wang, Yang; Hilboll, Andreas; Beirle, Steffen; Sihler, Holger; Puķīte, Jānis; Platt, U.; Wagner, Thomas

doi:10.5194/amt-2017-168

Cited by 3 publications

(3 citation statements)

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“…The wavelength shift can be caused by the tilt effect (typically < 2 pm) (Lampel et al, 2017a) and dominated by the mechanical deformation of a spectrometer, which is usually sensitive to variations of the ambient temperature. The averaged diurnal variations of the shifts derived from the fits with a daily noon FRS and a sequential FRS are smaller than 0.015 and 0.05 nm, respectively (the detailed results can be found in Fig.…”

Section: Results Of Hono Delta Scds and Dscds And Fit Errorsmentioning

confidence: 99%

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MAX-DOAS measurements of HONO slant column densities during the MAD-CAT campaign: inter-comparison, sensitivity studies on spectral analysis settings, and error budget

et al. 2017

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Abstract. In order to promote the development of the passive DOAS technique the Multi Axis DOAS -Comparison campaign for Aerosols and Trace gases (MAD-CAT) was held at the Max Planck Institute for Chemistry in Mainz, Germany, from June to October 2013. Here, we systematically compare the differential slant column densities (dSCDs) of nitrous acid (HONO) derived from measurements of seven different instruments. We also compare the tropospheric difference of SCDs (delta SCD) of HONO, namely the difference of the SCDs for the non-zenith observations and the zenith observation of the same elevation sequence. Different research groups analysed the spectra from their own instruments using their individual fit software. All the fit errors of HONO dSCDs from the instruments with cooled large-size detectors are mostly in the range of 0.1 to 0.3 × 10 15 molecules cm −2 for an integration time of 1 min. The fit error for the mini MAX-DOAS is around 0.7 × 10 15 molecules cm −2 . Although the HONO delta SCDs are normally smaller than 6 × 10 15 molecules cm −2 , consistent time series of HONO delta SCDs are retrieved from the measurements of different instruments. Both fits with a sequential Fraunhofer reference spectrum (FRS) and a daily noon FRS lead to similar consistency. Apart from the mini-MAX-DOAS, the systematic absolute differences of HONO delta SCDs between the instruments are smaller than 0.63 × 10 15 molecules cm −2 . The correlation coefficients are higher than 0.7 and the slopes of linear regressions deviate from unity by less than 16 % for the elevation angle of 1 • . The correlations decrease with an increase in elevation angle. All the participants also analysed synthetic spectra using the same baseline DOAS settings toPublished by Copernicus Publications on behalf of the European Geosciences Union. Y. Wang et al.: MAX-DOAS measurements of HONO slant column densitiesevaluate the systematic errors of HONO results from their respective fit programs. In general the errors are smaller than 0.3 × 10 15 molecules cm −2 , which is about half of the systematic difference between the real measurements.The differences of HONO delta SCDs retrieved in the selected three spectral ranges 335-361, 335-373 and 335-390 nm are considerable (up to 0.57 × 10 15 molecules cm −2 ) for both real measurements and synthetic spectra. We performed sensitivity studies to quantify the dominant systematic error sources and to find a recommended DOAS setting in the three spectral ranges. The results show that water vapour absorption, temperature and wavelength dependence of O 4 absorption, temperature dependence of Ring spectrum, and polynomial and intensity offset correction all together dominate the systematic errors. We recommend a fit range of 335-373 nm for HONO retrievals. In such fit range the overall systematic uncertainty is about 0.87 × 10 15 molecules cm −2 , much smaller than those in the other two ranges. The typical random uncertainty is estimated to be about 0.16 × 10 15 molecules cm −2 , which is only 25 % of the total syst...

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Section: Results Of Hono Delta Scds and Dscds And Fit Errorsmentioning

confidence: 99%

“…A description of the MAD-CAT measurement campaign can be found at http://joseba.mpch-mainz.mpg.de/ mad_cat.htm. Data from this campaign have been so far used in, for example, Ortega et al (2015), Lampel et al (2015Lampel et al ( , 2017a and Peters et al (2017).…”

Section: The Mad-cat Inter-comparison Campaignmentioning

confidence: 99%

MAX-DOAS measurements of HONO slant column densities during the MAD-CAT campaign: inter-comparison, sensitivity studies on spectral analysis settings, and error budget

et al. 2017

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“…These tests are used in the evaluations of the error budget in section 7.1. Although variations of the wavelength calibration do not occur for the synthetic spectra, the wavelength adjustment is still allowed in the DOAS fits to compensate for the tilt effect (Lampel et al, ).…”

Section: Feasibility Test Of the Two Retrieval Methods Based On Synthmentioning

confidence: 99%

Vertical Profiles of Tropospheric Ozone From MAX‐DOAS Measurements During the CINDI‐2 Campaign: Part 1—Development of a New Retrieval Algorithm

et al. 2018

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Ground‐based measurements of tropospheric ozone (O3) are valuable for studies of atmospheric chemistry, air pollution, climate change, and for satellite validation. The Multi Axis Differential Optical Absorption Spectroscopy (MAX‐DOAS) technique has been widely used to derive vertical profiles of trace gases and aerosols in the troposphere. However, tropospheric O3 has not yet been satisfactorily derived from MAX‐DOAS measurements due to the influence of stratospheric O3 absorption. In this study, we developed two new retrieval approaches for tropospheric O3 from MAX‐DOAS measurements. In method 1, stratospheric O3 profiles from external data sources are considered in the retrieval. In method 2, stratospheric and tropospheric O3 are separated based on the temperature‐dependent differences between tropospheric and stratospheric O3 absorption structures in the UV spectral range. The feasibility of both methods is first verified by applying them to synthetic spectra. Then they are applied to real MAX‐DOAS measurements recorded during the CINDI‐2 campaign in Cabauw, the Netherlands (September 2016). The obtained results are compared with independent O3 measurements and global chemical transport model simulations. Good agreement of the near‐surface O3 concentrations with the independent data sets is found for both methods. However, tropospheric O3 profiles are only reasonably derived using method 1, while they are significantly overestimated at altitudes above 1 km using method 2, probably due to the approximation of the ring spectra used to correct the rotational Raman scattering structures in the DOAS fit. Advantages and disadvantages of both methods are discussed and improvement directions are suggested for further studies.

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Investigating differences in DOAS retrieval codes using MAD-CAT campaign data

et al. 2017

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Abstract. The differential optical absorption spectroscopy (DOAS) method is a well-known remote sensing technique that is nowadays widely used for measurements of atmospheric trace gases, creating the need for harmonization and characterization efforts. In this study, an intercomparison exercise of DOAS retrieval codes from 17 international groups is presented, focusing on NO 2 slant columns. The study is based on data collected by one instrument during the MultiAxis DOAS Comparison campaign for Aerosols and Trace gases (MAD-CAT) in Mainz, Germany, in summer 2013. As data from the same instrument are used by all groups, the results are free of biases due to instrumental differences, which is in contrast to previous intercomparison exercises.While in general an excellent correlation of NO 2 slant columns between groups of > 99.98 % (noon reference fits) and > 99.2 % (sequential reference fits) for all elevation angles is found, differences between individual retrievals are as large as 8 % for NO 2 slant columns and 100 % for rms residuals in small elevation angles above the horizon.Comprehensive sensitivity studies revealed that absolute slant column differences result predominantly from the choice of the reference spectrum while relative differences originate from the numerical approach for solving the DOAS equation as well as the treatment of the slit function. Furthermore, differences in the implementation of the intensity offset correction were found to produce disagreements for measurements close to sunrise (8-10 % for NO 2 , 80 % for rms residual). The largest effect of ≈ 8 % difference in NO 2 was found to arise from the reference treatment; in particular for fits using a sequential reference. In terms of rms fit residual, the reference treatment has only a minor impact. In contrast, the wavelength calibration as well as the intensity offset correction were found to have the largest impact (up to 80 %) on rms residual while having only a minor impact on retrieved NO 2 slant columns.

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The tilt-effect in DOAS observations

Cited by 3 publications

References 23 publications

MAX-DOAS measurements of HONO slant column densities during the MAD-CAT campaign: inter-comparison, sensitivity studies on spectral analysis settings, and error budget

MAX-DOAS measurements of HONO slant column densities during the MAD-CAT campaign: inter-comparison, sensitivity studies on spectral analysis settings, and error budget

Vertical Profiles of Tropospheric Ozone From MAX‐DOAS Measurements During the CINDI‐2 Campaign: Part 1—Development of a New Retrieval Algorithm

Investigating differences in DOAS retrieval codes using MAD-CAT campaign data

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