Analysis Of Atmospheric Trace Gases Observation Along R/V Beijing Cruise Track

Observation of polar research vessels can obtain concentration data of trace gases in the ocean and atmosphere at different latitudes,thereby better reflecting the background changes of trace gases in the global atmosphere.However,during the ship’s navigation survey process,the concentration of trace gases in the atmosphere will be affected by local pollution from the ship itself or nearby ship engine exhaust emissions.In order to truly reflect the representative characteristics of the concentration of trace gases in the atmosphere over the ocean measured during the ship’s navigation process,an effective data screening method is needed to exclude the influence of local pollution.This article analyzes the original observation data of trace gases（CO,CO₂,O₃,CH₄,and N₂O）collected during the navigation process of the"Beijing"Antarctic research vessel between China and the new station in the Ross Sea in Antarctica from January 2020 to April 2020,and establishes an effective data screening method to exclude the influence of local pollution,thus obtaining a data set that can represent the background of trace gases in the ocean and atmosphere.Based on this,the distribution characteristics of trace gas concentrations on the route are studied.The following results were obtained:1)During the navigation survey process of the ocean-going ship,the concentrations of atmospheric CO,CO₂,and O₃ are significantly affected by local pollution,but CH₄ and N₂O are affected the least.The adjacent 1-minute concentration difference threshold method can effectively remove the abnormal values in the CH₄ and N₂O data sequences.In clean areas,the combined（CO₂+CO）tracing method is the optimal combination for screening the values of CO₂,CO,and O₃ affected by local pollution.In the southern region of the Southern Ocean,after removing the influence of local pollution,the average values of CO and CO₂ are reduced by（5～11）n L·L^-1（10%～18%）and（3～7）μL·L^-1（1%～2%）,respectively,while O₃ increases by 3～5μL·L^-1（20%～25%）,thus ensuring the global background characteristics of observation data.In areas with high local pollution,the（CO₂+CO）tracing method is not effective,but the CO/CO₂ tracing method is the most effective for screening the concentrations of CO and CO₂.2)The greenhouse gases in the near-ocean surface between the Bohai Sea and the Ross Sea in Antarctica show a north-high and south-low distribution pattern with latitude.When comparing CO₂,CH₄,and N₂O with assimilated data of the same latitude station and global ocean boundary layer greenhouse gases（GLOBALVIEW）,the concentration difference between ship measurement data and comparison data is generally less than 2 n/μL.L^-1 in the southern hemisphere and the ITCZ（Inter Tropical Convergence Zone）region,while it deviates greatly in the northern hemisphere,and the smallest deviation of CH4 in the northern hemisphere reaches more than 10 n L.L^-1.3)Based on China’s polar research data,this article concludes that the average growth rates of CO₂ in the atmosphere in the northern and southern hemispheres from November 2014 to January 2020 are 3.9μL.L^-1 and 2.5μL.L^-1,respectively,and those of CH₄ are 15.5 n L.L^-1 and 7.6 n L.L^-1,respectively.From November 2005 to January2020,the average growth rates of N₂O in the northern and southern hemispheres are1.27 n L.L^-1 and 1.26 n L.L^-1,respectively.This result is higher than the growth rates given by IPCC6,which are 2.4μL.L^-1,7.9 n L.L^-1,and 1.0 n L.L^-1,respectively.4)The transport of trace gases in the atmosphere from the northern hemisphere to the south can cross the equator to the north boundary of the ITCZ at 5°S,and the southernmost region affected is 15°S.The ITCZ is an important transition zone where the concentration of greenhouse gases in the ocean surface decreases from high values to the average concentration in the southern hemisphere.5)The atmospheric O₃ near the ocean surface shows several significant regional distribution characteristics:it is highly polluted in the Yellow Sea and the East China Sea(>50 n L.L^-1),which is caused by long-distance transport of polluted air masses from the mainland of East Asia and nearby waters;during the return journey,it is significantly low(<5.0 n L.L^-1)in the 6-14°S region of the southern hemisphere,while other gases do not show significant concentration changes.This phenomenon is related to the low ozone value area in the ITCZ region.During the outbound journey,it increased by nearly 1.5 n L.L^-1 due to forest fires on the eastern coast of Australia,while it increased by nearly 6 n L.L^-1in the 55-60°S region due to the downward transport of UT-LS（Upper troposphere-Lower stratosphere）,but N₂O decreased by 0.5 n L.L^-1.