Concentration of gaseous methanesulfonic acid measured over the Southern Ocean in the austral summer of 2016/2017, during the Antarctic Circumnavigation Expedition (ACE). Data files: gas_methanesulfonic_acid_concentration_data.csv File header date_time: start time of five-minute averaging period in ISO 8601 format YYYY-MM-DDThh:mm:ss+00:00 [UTC] methanesulfonic_acid_concentration: Gaseous methanesulfonic acid concentration measured with a nitrate chemical ionization APi-HTOF mass spectrometer [molecules per cm^3] flag: data quality flag, 1 indicates good data whereas 0 indicates data contaminated by the ship exhaust latitude: median ship latitude during the five-minute averaging period as measured by the ship GPS [decimal degrees N] longitude: median ship longitude during the five-minute averaging period as measured by the ship GPS [decimal degrees E]