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二氧化碳(CO2)是大气中最重要的长寿命温室气体。受化石燃料燃烧、土地利用变化、森林砍伐等人为活动的持续影响,全球大气中CO2混合比已由工业革命前期(1750年)的约280×10−6(混合比)上升至2019年的(410.50 ± 0.10)×10−6[1],由此导致全球变暖、海平面上升和海洋酸化等一系列气候与环境变化问题[2]。同时,科学界也认识到高精度高时空分辨率的观测研究,是厘清CO2源汇过程,探究和预测气候与环境变化,进而科学实施CO2减排和实现碳中和的基础。
大气CO2观测方式包括陆(岛)基观测站的定点时间序列观测、大气垂直廓线观测(如高塔分层采样观测)、冰芯采样观测、表层海水与上覆大气间通量观测、卫星遥感观测、移动平台观测(如飞机、船舶和汽车等)等[3]。船基移动观测是开展海洋大气温室气体海-气交换通量研究和海-陆输送过程分析的重要方式[4]。20世纪80年代以来,日本气象厅在西太平洋开展了逐年的海洋大气CH4船基离散采样观测研究,结果显示,西太平洋海表大气CH4呈明显的纬向分布特征,即海表大气CH4混合比随纬度增加而升高[5]。2009年以来,欧美日发达国家和我国科研院校先后利用光腔衰荡光谱分析仪或离轴积分腔输出光谱分析仪等高频高精度观测设备,开展海洋大气温室气体(CO2和CH4等)船基走航连续观测,并利用海洋油气平台下风向观测的CO2和CH4峰值信号,初步构建“自上而下”估算方法,针对性定量探究了海洋油气开采对大气温室气体的贡献[6-9]。
我国拥有300多万平方公里的管辖海域,海洋油气开采、海上航运和海水养殖等人为活动可能影响局地乃至区域海洋大气温室气体的时空分布特征,但海洋温室气体观测研究长期侧重于海-气交换通量,而针对海洋大气温室气体的观测研究起步较晚,观测方法和标准各异[10]。2008年,渤海湾近岸海域的船基离散采样观测显示,CH4、N2O和CO2混合比受局地陆-海气团输送影响,具有较强的人为源影响特征,且季节差异明显[11]。2012年起,我国开始船基走航式高频高精度连续观测,解析近海大气温室气体的时空分布特征和调控机理[9,12]。但由于我国近海大气温室气体时空分布受海-陆输送、海-气交换、船舶排放和海洋油气开采等自然和人为过程的多重耦合影响,因此有必要优化建立适用于船基走航高频高精度连续观测的数据质控方法,特别是数据筛分方法,以更准确地开展自然和人为源汇过程的定性定量研究。
本研究基于2013年春季我国近海大气CO2船基走航高频高精度连续观测数据,开展数据筛分处理方法研究,以期精准区分各种自然及人为过程对海洋大气CO2时空分布的影响,进而获取精细化温室气体观测研究产品,推进科学碳减排措施,为实现碳中和提供技术支撑[13]。
海洋大气二氧化碳船基走航连续观测数据的质量控制方法
Study of data quality assurance/control on the shipborne continuous CO2 observations
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摘要: 船基走航连续观测是掌握海洋大气温室气体含量及特征的重要方式之一。为准确掌握海表大气温室气体时空变率,必须建立科学的数据质量控制方法。本研究基于2013年春季在我国近海开展的海洋大气CO2船基走航连续观测数据,充分结合现场操作记录、气象要素、航速航向、拉依达准则和气团后向轨迹模拟结果等数据及技术手段,开展CO2观测数据的筛分处理方法研究。本研究优化建立的方法可标记仪器故障、人为操作和船体排放等因素导致的异常观测值。对走航期间近海CO2混合比分析结果显示,我国近海大气CO2的纬向分布与北半球MBL的CO2模拟结果具有一致性,但受来自欧亚大陆气团的影响,导致我国近海与MBL的CO2混合比之差随纬度增加而上升。Abstract: Shipborne continuous observation is widely adopted as an important approach to understand the variation of greenhouse gases in the marine boundary layer (MBL). In order to precisely understand the spatiotemporal variation of greenhouse gases in the MBL, a scientific data quality control approach should be established. Based on the shipborne continuous CO2 observations over the China shelf seas in spring of 2013, in this study, a new data filtering method was developed by considering the operation log, meteorological parameters, pauta criterion, and air mass transport, which could efficiently mark the CO2 observations influenced by instrument malfunction, ship emissions, and refillting of drying-tube, etc. Our filtered results showed that the latitudinal distribution of atmospheric CO2 in China shelf seas agreed well with the simulated distribution of MBL-CO2 in northern hemisphere. Additionally, we concluded that, the CO2 discrepancy between the China shelf seas and MBL enlarged along with increasing latitude, which was likely due to the transportion of air mass from the Eurasian continent.
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Key words:
- marine boundary layer /
- carbon dioxide /
- shipborne observation /
- data quality control /
- data filtering
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