Observations of atmospheric trace gases along the R/V Beijing cruise track between China and Antarctica: Data QA/QC and preliminary results

Atmospheric chemistry observations aboard ships are vulnerable to pollution from ship fuel engine exhaust. This local pollution leads to an increase in CO and CO₂ and a decrease in O₃. Concentrations (presented as volume mixing ratio) of CO, CO₂, O₃, CH₄ and N₂O in the marine-atmosphere boundary layer were measured along the R/V Beijing cruise track between Bohai bay of China and the Ross sea in Antarctica from January to April 2020. Based on the successive observations of 1-minute resolution, the impact of local pollution emission on the measured values of each trace gas is respectively implied by the persistence of variations in CO, CO₂, and combinations of CO and CO₂ and CO/CO₂ for the study of data quality assessment quality controls (QA/QC). The results show that CO, CO₂ and O₃ (CH₄ and N₂O) data are significantly (slightly) contaminated by local pollution. A method of trace concentration difference threshold between any immediate adjacent 1-minute is proposed, which can effectively remove the outliers of CH₄ and N₂O from their time series datasets. The pollution period implied by CO or CO₂ can be partially but not completely used to identify the contaminations in the dataset. The ratio of CO/CO₂ implication can effectively determine the global baseline concentration of CO or CO₂ in highly polluted region but at a high cost of discarding many data samples. The combination of CO₂ and CO (CO₂+CO) is the best method to imply the pollution signals in the CO₂, CO and O₃ datasets, and this method decreases the measured values of CO and CO₂ concentrations in the southern hemisphere and the pristine region by (5—11)×10⁻⁹ (10%—18%) and (3—7)×10⁻⁶ (1%—2%) respectively, while O₃ increases by (3—5)×10⁻⁹ (20%—25%). The final version concentration data of each trace gas are reasonably comparable with those measured at continental sites and the concentration differences of CO, CO₂, CH₄ and N₂O in the southern ocean and Antarctica are respectively within 2×10⁻⁹, 0.7 ×10⁻⁶, 1.4×10⁻⁹ and 0.5×10⁻⁹. All the atmospheric trace gases data after QA/QC display their concentration features of high (low) in the northern (southern) hemisphere, and they remain stable in the south of the Southern Ocean and Antarctica region. Additionally, regional distribution characteristics of atmospheric O₃ and their mechanisms are quite reasonable. All these reflect the rationality and accuracy of the proposed QA/QC method applied for the trace gases observations along the R/V Beijing cruise.