Raw spectra measurements of scattered sunlight collected using a MAX-DOAS (Multi-Axis Differential Optical Absorption Spectroscopy) instrument in the austral summer of 2016/17 during the Antarctic Circumnavigation Expedition (ACE). ***** Dataset abstract ***** To achieve the objectives of the project, we installed a MAX-DOAS (Multi-AXis Differential Optical Absorption Spectroscopy) instrument on the vessel “Akademik Tryoshnikov”. This instrument is based on the DOAS technique, which is used to measure trace gas concentrations in the atmosphere. The method consists of the analysis of the spectral absorption lines that each trace gas produces in the solar spectra. The DOAS technique uses the narrowband features that every trace gas has in their spectral absorption coefficients. This differential cross section is unique and acts like a fingerprint for the trace gases, allowing to differentiate between them and to estimate their concentrations (for further details see Platt and Stutz, 2008). In the past decades, atmospheric chemists have come to realize that halogen species (like Cl, Br or I and their oxides ClO, BrO and IO) exert a powerful influence on the chemical composition of the troposphere and through that influence affect the evolution of pollutants, hence having a significant impact on climate. These reactive halogen species are potent oxidizers for organic and inorganic compounds throughout the troposphere. In particular, halogen cycles can act on several compounds (such as methane, ozone, particles…), all of which are climate forcing agents through direct and indirect radiative effects. Dynamic exchange of halogens between the ocean, sea ice, snowpack and atmosphere is the main driver for the frequent occurrence of Ozone Depletion Events (ODEs) and Atmospheric Mercury Depletion Events (AMDEs) (Saiz-Lopez and von Glasow, 2012). In this dataset we present the raw spectra measurements of scattered sunlight recorded by the MAX-DOAS onboard a research vessel in the Southern Ocean and Atlantic Ocean. Included are position and vessel inclination data. Data coverage is from December 2016 to April 2017. ***** Original data collection ***** The data was collected by a MAX-DOAS instrument, which collects scattered sunlight at different elevation viewing angles. The instrument was installed on board the R/V Akademik Tryoshnikov to measure scattered sunlight. It was built in the scientific laboratory (Atmospheric Chemistry and Climate, AC2), and it comprises two parts. The first one is the scanning telescope system, which is placed outside on the second deck of the ship, with a clear view of the horizon. It consists of a weatherproof metal chamber that is located on top of a stabilization system (gimbal table) in order to counteract the ship movements. Moreover, a GPS was also installed in order to save the latitude and longitude of the ship during the circumnavigation (resulting files named GPS_JDDD.txt). Additionally, an inclinometer was also attached to the gimbal table to record the actual pitch and roll of the instrument with the purpose of correcting the elevation viewing angles afterwards (resulting files named Inclination_JDDD.txt). The metal chamber has a light collector that receives scattered sunlight. The incoming light is focused by a lens (F = 200 mm, diameter of 50.8 mm) onto an optical fiber which has 19 individual quartz fibers. The optical fiber is then connected to the second part (indoor), which comprises a spectrometer (Princeton Instruments SP500i), a charge-coupled device detector (CCD camera Princeton Instruments Pixis 400B) and a computer. Once in the spectrometer, the light is diffracted and dispersed by a 600 groove/mm grating resulting in a spectral window of 90 nm. This indoor part is located in a temperature-controlled laboratory. The instrument electronic offset and dark current are subtracted from each spectrum. The exposure time is adjusted automatically depending on the sunlight intensity in order to optimize the signal to noise ratio. It should be noted that scattered sunlight measurements can be strongly affected by clouds, mainly due to multiple scattering effects that give rise to large uncertainties in the light path retrieval. For this reason, we installed a camera alongside the MAX-DOAS in order to take live pictures of the sky every 5 minutes to evaluate a cloud index, which goes from 0 (clear sky) to 10 (completely overcast) (Benavent et al., 2020; DOI: 10.5281/zenodo.3827445). The cloud index was revised and noted manually for each image in turn. Only spectra with a cloud index below 4 are taken into account for further analysis. Data was collected using in-house software which is responsible for saving the data and keep the instrument running. Finally, the spectra were saved for both spectral regions (UV and VIS) in ASCII text files. In the folders called Spectra there are two sub-folders inside, one of them called MAXDOAS and the second one called ZENITH. The MAXDOAS folder has the spectra taken from a Solar Zenith Angle (SZA) up to 85 degrees and pointing at different elevation viewing angles; this contains two folders: 358 (spectra taken in the UV region) and 440 (spectra taken in the VIS region) and in this directory there are folders for the different day of the year. If you are interested in the spectra of one day, you can visit the Atmos folder inside the day, and there is an ASCII file for each spectrum. Moreover, the file LiveInfo provides some spectra characteristics for this day. The folder named ZENITH contains spectra taken between a SZA from 85 degrees to 95 degrees, and the MAX-DOAS is only pointing in zenith direction (elevation viewing angle of 90 degrees). This directory contains the same structure as for MAXDOAS folder. Before the campaign, we calibrated the wavelength of the spectrometer. The method we used to do it was measuring the positions of atomic emission lines (Hg-Ne lamp) of known wavelengths. The atomic emission lines could be treated as delta functions; the Princeton software adjusts the individual lamp emission lines as a Gaussian function to determine the centre position and it automatically corrects if there is some wavelength shift. Data are missing from the following days (JDDD - Julian day): - MAXDOAS 358 nm: J8, J32, J37, J39-J43, J45, J60-J65, J79 - MAXDOAS 440 nm: J362, J8, J32, J37, J39-J43, J45, J60-J65, J79 - ZENITH 440 nm: J362, J7, J8, J31, J36-J45, J60-J65, J79 ***** Data processing ***** No data processing was undertaken. ***** Quality checking ***** No quality checking was undertaken. ***** Standards ***** This dataset uses widely accepted standards for atmospheric sciences. ***** Dataset contents ***** ace_maxdoas_gps.zip - GPS_JDDD.txt, data file, ASCII text ace_maxdoas_inclination.zip - Inclination_JDDD.txt, data file, ASCII text ace_maxdoas_spectra-YYYY-MM.zip - MAXDOAS - - WWW - - - JDDD - - - - LiveInfo_DDDhhmmss.WWW, data file, ASCII text - - - - Atmos - - - - - DDDhhmmss_90.WWW, data file, ASCII text - ZENITH - - WWW - - - JDDD - - - - LiveInfo_DDDhhmmss.WWW, data file, ASCII text - - - - Atmos - - - - - DDDhhmmss_90.WWW, data file, ASCII text - README.txt, metadata, text - data_file_header_gps.txt, metadata, text - data_file_header_inclination.txt, metadata, text - data_file_header_spectra_atmos.txt, metadata, text - data_file_header_spectra_liveinfo.txt, metadata, text where YYYY is the year and MM is the month. JDDD is the day of the year (Julian day) YYYY in which the file was recorded. hhmmss is the time. WWW is the central wavelength of the measured spectrum in the UV or VIS region. ***** Dataset contact ***** Alfonso Saiz-Lopez, Department of Atmospheric Chemistry and Climate, Spanish National Research Council (CSIC). ORCID: 0000-0002-0060-1581. Email: a.saiz@csic.es ***** Dataset license***** This dataset of raw spectra of scattered sunlight measurements from ACE is made available under the Creative Commons Attribution 4.0 International License (CC BY 4.0) whose full text can be found at https://creativecommons.org/licenses/by/4.0/ ***** Dataset citation ***** Please cite this dataset as: Benavent, N., Garcia-Nieto, D., Cuevas, C.A. and Saiz-Lopez, A. (2020). Raw spectra measurements of scattered sunlight collected using a MAX-DOAS (Multi-Axis Differential Optical Absorption Spectroscopy) instrument in the austral summer of 2016/17 during the Antarctic Circumnavigation Expedition (ACE). (Version 1.0) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.3827443