Aerosol particle number concentration 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 aerosol particle number concentration with a condensation particle counter CPC model TSI 3022 at a time resolution of 10 seconds during the Antarctic Circumnavigation Expedition (ACE). We report five-minute averaged data cleaned from exhaust gas influence. The lower cut-off of the CPC is 7 nm. Temporal coverage of the dataset is from December 20, 2016 to April 10, 2017. 

The total particle number concentration reflects aerosol particles from a variety of sources and processes. The concentrations include for example sea spray aerosol, long-range transported particles, newly formed particles and others. The variability in the concentration reflects processes such as wet removal through precipitation, new particle formation or sea spray formation.

***** Original data collection *****

We operated a TSI Condensation Particle Counter (CPC), model 3022 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 (PSI) situated on the foredeck of the R/V Akademik Tryoshnikov. More about this set-up can be found in the cruise report here: https://doi.org/10.5281/zenodo.1443511.

Original output was stored as text files in 10 second intervals on a computer situated in the PSI laboratory container. 

The data acquisition software was custom-programmed in LabView by Martin Gysel-Beer, at the Paul Scherrer Institute, Switzerland.

There was no data processing during collection.

***** Data processing *****

Data were processed in Igor Pro (version 6.37; WaveMetrics, Portland, OR, USA). Further information about the data processing can be found in the quality checking section below.

***** Quality checking *****

The CPC was intercompared with the other CPCs operated during the campaign on the dates listed below. Deviation between the concentrations of < 10 % measured by the different CPCs is considered to be within the expected uncertainty (Schmale et al., 2017). The deviation was 12 % from the average of the other CPCs. The data was corrected by dividing by 0.88. 
23.01.2017
10.03.2018
09.05.2017

The data were 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 aerosol particle number concentrations are within +/- 10 % uncertainty. The number concentrations have been corrected for line losses. Line losses were determined experimentally and are size dependent. Since the CPC does not provide particle size information, a correction factor was derived from size-resolved measurements with a scanning mobility particle sizer (SMPS). For the acquisition and correction of the SMPS data please see the dataset with DOI: 10.5281/zenodo.2636700. The correction factor was derived by the following equation:  

f(CPC) = int[SMPS(corr)] / int[SMPS(theolossCPCline)]

With f(CPC) = the correction factor for the CPC. SMPS(corr) is the loss corrected particle size distribution which is integrated and divided by the integrated SMPS size distribution, SMPS(theolossCPCline), accounting for the size dependent losses of the CPC inlet line. The correction is in the order of 10 to 20 %. Higher losses occur when the fraction of smaller particles is larger. 

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 as described in Schmale et al., 2017.

***** Further information for interpreting and using the dataset *****

Detection limit: All reported data are above detection limit. 

Timescales: The timescales of the main phenomena of the dataset vary from minutes (new particle formation) to hours (particle growth) to days (synoptic weather systems that remove particles through precipitation). 

Interpolation: Interpolation of missing values is NOT meaningful due to the inherently high variability.

Aggregation to lower temporal resolution: 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, in review) “Overview of the Antarctic Circumnavigation Expedition Study of Preindustrial-like Aerosols and their Climate Effects (ACE-SPACE)”.

***** Dataset contents *****

- ACESPACE_aerosol_particle_concentration.csv, data file, comma-separated values
- data_file_header.txt, metadata, text
- README.md, metadata, text

NaN values of aerosol particle number concentration denote missing values because of e.g., ship exhaust contamination, maintenance, instrument failure. 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. ORCID: 0000-0002-1048-7962 julia.schmale@psi.ch

***** Dataset license *****

This ACESPACE aerosol particle number concentration dataset is made available under the Open Data Commons Attribution License: https://opendatacommons.org/licenses/by/1.0/index.html.

***** 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. (2019). Aerosol particle number concentration measured over the Southern Ocean in the austral summer of 2016/2017, during the Antarctic Circumnavigation Expedition. (Version 1.0) [Data set]. Zenodo. http://doi.org/10.5281/zenodo.2636690