Trace gas mixing ratios measured over the Southern Ocean in the austral summer of 2016/2017, during the Antarctic Circumnavigation Expedition. ***** Dataset abstract ***** The authors would highly appreciate to be contacted if the data is used for any purpose. We measured mixing ratios of CO, CO2 and CH4 with a PICARRO G2401 Gas Analyzer. Ozone (O3) mixing ratios were measured with a 2B Technology ozone monitor, model 205. We report five-minute averaged data cleaned from exhaust gas influence. Temporal coverage is from December 20, 2016 to April 10, 2017. The trace gas concentrations represent a large number of atmospheric processes that happen on different time scales. CO for example, has basically no sources other than combustion and can hence be used as tracer for air mass transport from regions with combustion activities (e.g., South Africa). CO has a lifetime of a few weeks. CO2 and CH4 are longer-lived trace gases which disperse globally. The data set shows that concentrations in the Northern Hemisphere are higher than in the Southern Hemisphere. Both trace gases are emitted by anthropogenic activities as well as natural sources. Over the cruise track, areas of the Southern Ocean were passed where these trace gases either outgas or are absorbed. Ozone is a secondary trace gas, meaning that it is formed in the atmosphere. Its concentrations are relatively low. All trace gases data have been cleaned from exhaust gas influence. ***** Original data collection ***** We measured mixing ratios of CO, CO2 and CH4 with a PICARRO G2401 Gas Analyzer. Ozone (O3) mixing ratios were measured with a 2B Technology ozone monitor, model 205. We operated the instruments behind a standard Global Atmosphere Watch whole air inlet (Schmale et al., 2017; 10.1038/sdata.2017.3) in an aerosol container constructed by the Paul Scherrer Institute situated on the foredeck of the R/V Akademik Tryoshnikov. The PICARRO instrument has an internal filter to prevent clogging of the instrument. The ozone monitor was operated behind a Teflon filter to prevent particles from entering the instrument. More about this set-up can be found in the cruise report here: https://doi.org/10.5281/zenodo.1443511. Original output from the ozone monitor was stored as text files in 10-second intervals on a computer situated in the PSI laboratory container. Each file contains data for 24 hours. Original output from the PICARRO instrument was stored on the instrument’s internal computer with one-second time resolution. The data acquisition software for the ozone monitor is custom-programmed in LabView by the Paul Scherrer Institute, Switzerland. The PICARRO instrument acquired data with the standard PICARRO analyzer GUI functions delivered with the instrument. There is no data processing during collection for the ozone instrument. The PICARRO GUI provides a dry air value for the CH4 and CO2 mixing ratios based on the measurements of water vapour by the instrument. The reported data is based on the dry data sets. ***** Data processing ***** Data were processed in Igor Pro v6.37 (WaveMetrics Inc.). For more details about how the data were processed, see the quality checking section. ***** Quality checking ***** The PICARRO instrument was calibrated with references gases in June 2017 after the return of the expedition. The following corrections were applied to the gases: CO2 reported = CO2 measured * 0.988 + 0.350 CO reported = CO measured * 1.027 - 0.002 CH4 reported = CH4 measured * 1.010 + 0.027 The ozone monitor was compared to a reference instrument in June 2017 and mixing ratios were corrected as follows: O3 reported = (O3 measured – 1.97) / 1.08 The data have been cleaned from exhaust gas based on the spikiness of the total particle number concentration and the CO2 concentrations (10.5281/zenodo.2636690, 10.5281/zenodo.2636779, respectively). Exhaust influence on the data was identified as follows: The particle number concentration as measured by the CPC 3022 was used as the basis. First the absolute value of the ratio of the raw over the smoothed signal (running average over 12 points for five-minute time resolution data, which represents a curve similar to a baseline) was calculated. Ratio values that are larger than 1.24 and smaller 0.51 were flagged. The same was done for ratios of the raw and smoothed CO2 data with the thresholds being 1.2 and 0.8. In addition, since exhaust influence is characterized by abrupt concentration changes, subsequent values of the raw particle number concentration time series that were more than 50 cm^-3 apart were flagged. Finally, the flagged and original time series were compared by eye to identify any further values influenced by exhaust. The natural variability in number concentration is evident in timescales of hours rather than seconds, which are characteristics for exhaust plumes. New particle formation events can happen on timescales shorter than one hour: those were not eliminated. The ozone monitor measures with a precision of higher than 0.2 ppb for five-minute averaged data (the 10-second value is provided by the manufacturer). Given that the mixing ratios have been corrected with a reference instrument and that mixing ratios are generally higher than 5 ppb, the accuracy of the mixing ratios is +/- 4 %. Precision of the PICARRO gas analyser for five-minute data is 1.5 ppb for CO, 20 ppb for CO2, and 0.5 ppb for CH4 (given by the manufacturer). After correction of the data based on above mentioned calibration we estimate the accuracy as follows: For 20 ppb CO, accuracy is around +/- 7.5 % For 385 ppm CO2, accuracy is > +/- 0.001 % For 1.8 ppm CH4, accuracy is around +/- 0.2 % Data quality can be assessed only during calibrations and instrument intercomparisons but not by only using this data set. ***** Standards ***** We follow the best practice that we are aware of in the respective scientific community ***** Further information for interpreting and using the dataset ***** Detection limit: All reported data are above detection limit. Timescales: Time scales of the main phenomena in the data can vary from seconds (formation of ozone or depletion, emission of any other gas), over minutes (outgassing or absorbing ocean section) to days. Interpolation: Interpolation of missing values is NOT meaningful due to the inherently high variability. Aggregation to lower temporal resoltion: This depends on the research question. The data set features a number of environmental processes that happen on timescales from minutes to days. Averaging will eliminate shorter term signals, but could emphasize longer term features. For more information, see Schmale et al. (2019) “Overview of the Antarctic Circumnavigation Expedition Study of Preindustrial-like Aerosols and their Climate Effects (ACE-SPACE)”. ***** Dataset contents ***** - ACESPACE_trace_gas_concentration.csv, data file, comma-separated values - data_file_header.txt, metadata, text - README.txt, metadata, text - change_log.txt, metadata, text NaN values denote missing values because of e.g., ship exhaust contamination or instrument maintenance. For latitude and longitude, NaN values are noted in cases where position data was not available for the given time period. ***** Dataset contact ***** Julia Schmale, Paul Scherrer Institute, Switzerland. ORCID: 0000-0002-1048-7962. julia.schmale@psi.ch ***** Dataset license ***** This trace as mixing ratio dataset 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: Schmale, J., Henning, S., Tummon, F., Hartmann, M., Baccarini, A., Welti, A., Lehtipalo, K., Tatzelt, C. and Gysel-Beer, M. (2020). Trace gas mixing ratios measured over the Southern Ocean in the austral summer of 2016/2017, during the Antarctic Circumnavigation Expedition. (Version 1.1) [Data set]. Zenodo. http://doi.org/10.5281/zenodo.4028749