Carbon dioxide dry air mole fractions measured in the Swiss container during MOSAiC 2019/2020

This dataset contains carbon dioxide dry air mole fractions measured during the year-long 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 cavity ring-down spectroscopy using a commercial Picarro instrument (model G2401). The minute-averaged dry air mole fractions were adjusted after cross-evaluation against discrete whole air samples collected for post-cruise analysis at the National Oceanic and Atmospheric Administration (NOAA) Global Monitoring Laboratory. Pollution 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 result of these two steps is the “reference” time-series. The standard deviation of the difference between values and the reference is then calculated. 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 original carbon dioxide dry air mole fraction in µmol/mol, the adjusted carbon dioxide dry air mole fraction in µmol/mol after cross-evaluation, and a pollution flag where 'yes' means that local pollution was detected.

本数据集收录了2019年10月至2020年9月为期一年的MOSAiC（北极多学科漂流气候考察）远征期间测得的二氧化碳干空气摩尔分数。测量工作在极星号（Research Vessel Polarstern）科考船D甲板的瑞士集装箱内完成，数据采用商用Picarro（型号G2401）仪器通过腔衰荡光谱法采集得到。经与美国国家海洋和大气管理局（National Oceanic and Atmospheric Administration，NOAA）全球监测实验室为航后分析采集的离散全空气样品进行交叉比对评估后，对分钟平均干空气摩尔分数进行了校准修正。由本地人为污染源（如科考船发动机及排气口尾气、雪地摩托、直升机、冰上柴油发电机）引发的污染尖峰，按如下方式识别并标记：针对每个数据点，计算其梯度（时间导数）（Beck等人，2022）；梯度异常偏高（超过四分位距1.5倍）的数据点及其邻近点将被剔除。随后采用R语言oce包（版本1.3-0）中的"despike"函数对时间序列进行处理，以去除剩余的本地污染尖峰。简言之，该函数首先对序列中的缺失值间隙进行线性插值；随后计算覆盖k个元素的滑动中位数，由此得到的结果即为"参考"时间序列。之后计算实测值与参考值差值的标准差，将与参考值偏差超过该标准差n倍的数据点判定为尖峰并予以剔除。本次处理中，该函数的参数设置为n=1、k=61（对应约1小时的窗口）。数据集包含以下数据列：协调世界时（Coordinated Universal Time，UTC）格式的日期与时间、极星号科考船的经纬度、MOSAiC事件标签、原始二氧化碳干空气摩尔分数（单位：µmol/mol）、经交叉评估校准后的二氧化碳干空气摩尔分数（单位：µmol/mol），以及污染标记列（"yes"表示检测到本地污染）。