不同源汇信息提取方法对区域CO2源汇估算及其季节变化的影响评估

从大气二氧化碳(CO2)浓度观测资料中准确提取源汇或本底信息对区域及全球碳源汇及大气CO2浓度长期变化趋势的定量估计至关重要.本研究以瓦里关大气CO2浓度观测资料为例,探讨了同期地面风和同期一氧化碳(CO)浓度观测资料作为源汇信息提取或本底值筛选因子的有效性.结果表明,地面风和同期CO浓度在冬季可作为筛选因子,但是夏季将其作为筛选因子不是十分有效.采用局部近似回归法(robust estimation of background signal,REBS)、傅里叶变换法(Fourier transform algorithm,FTA)和新发展的平均移动过滤法(moving average filtering,MAF)进行大气CO2浓度源汇及本底信息提取.结果表明,MAF法因其以每2周为一个拟合窗口,采用不断变化和调整的过滤标准,避免了在局部将抬升浓度或吸收浓度百分比过高或者过低估计,优于另外两种方法.3种方法对因区域排放源导致的大气CO2的抬升量的结果无显著差异,但对因区域吸收汇导致的大气CO2降低量差异明显.结果表明,3种方法均可以对受到人类活动排放源影响的CO2抬升浓度合理地筛分,但只有MAF法可对夏季吸收浓度较好地判别.MAF法获得的1995~2008年瓦里关大气CO2多年平均季振幅为约10.3×10-6(摩尔分数,下同),与前期观测结果一致;而REBS法得到的大气CO2逐年季振幅约为9.1×10-6,将会导致低估区域或全球CO2通量值.

Evaluation on the Impacts of Different Background Determination Methods on CO2 Sources and Sinks Estimation and Seasonal Variations

To accurately determine background conditions or extract sources and sinks information from the observed atmospheric carbon dioxide (CO₂) concentration is crucial for quantitative estimation of regional and global carbon budget and future trends of atmospheric CO₂. In this study, the synchronized observed surface winds and carbon monoxide (CO) concentration have been examined to test their effectiveness as filter factors to determine CO₂ background conditions at Waliguan site. The results show that the surface winds and CO concentrations can be used as filter factor in winter, but they are not very effective in summer. Three statistical methods, robust estimation of background signal (REBS), Fourier transform algorithm (FTA) and a new developed moving average filtering (MAF), are applied to atmospheric CO₂ background selection. The result suggested that our new developed MAF method, which can well estimate the elevated and sequestered CO₂ concentrations due to using changing and adjusting filter criteria at every two-week fitting window, is thus better than the other two statistical methods. A good consistency is indicated by the three methods for estimating the elevated CO₂ caused by local or regional emissions, but it showed large discrepancies when determining the sequestered CO₂. The result suggested that the three methods can reasonable extract those anthropogenic influenced episodes, but only MAF method would well identify those episodes due to terrestrial CO₂ fluxes. Mean seasonal amplitude of atmospheric CO₂ at Waliguan during 1995-2008 is 10.3×10^-6 estimated by MAF method, which is in good agreement with previous studies. Whereas, the seasonal amplitudes derived by REBS method are much lower, only with a value of ~9.1×10^-6 during 1995-2008, which will result in an underestimation of regional or global CO₂ fluxes.