Ambient air sulfur dioxide mole fractions measured in the Swiss container during MOSAiC 2019/2020

This dataset contains minute-averaged sulfur dioxide mole fractions measured during the year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition from October 2019 to September 2020. The measurements were performed in the Swiss container on the D-deck of Research Vessel Polarstern. Data were collected by pulsed fluorescence using a Thermo Fisher Scientific instrument (model 43i). The minute-resolution mole fractions were adjusted after cross-evaluation against a certified sulfur dioxide standard at the end of the expedition at the Swiss Laboratories for Materials Science and Technology (EMPA). Spikes due to local anthropogenic pollution sources (e.g., exhaust by the vessel's engine and vents, skidoos, helicopters, on-ice diesel generators) were identified and flagged as follows. For each data point, the gradient (time derivative) was calculated (Beck et al., 2022). Data points corresponding to an abnormally high gradient (> 1.5 times the interquartile range) and neighboring points were discarded. The function “despike” from R package oce (version 1.3-0) was then applied to the time-series to remove any remaining local pollution spikes. Briefly, this function first linearly interpolates across any gaps (missing values). Then, it calculates a running median spanning k elements. The standard deviation of the difference between values and the reference is then calculated. The result of these two steps is the “reference” time-series. Values that differ from the reference by more than n times this standard deviation are considered to be spikes and eliminated. The function was applied once with n = 1 and k = 61 (~ 1 hour). The data columns include the Date and Time in Coordinated Universal Time (UTC), the latitude and longitude of Research Vessel Polarstern, the MOSAiC event label, the sulfur dioxide mole fractions in nmol/mol, a pollution flag where 'yes' means that local pollution was detected, and a detection limit flag where 'yes' indicates that the concentration was below the lower detectable limit of 1 nmol/mol.