Outliers are frequent in CO₂ and CH₄ observations at rural sites. The aim of this paper is to establish a procedure based on the lag-1 autocorrelation to form measurement groups, some of which include outliers, and the rest include regular measurements. Once observations are classified, a second objective is to determine the number of harmonics in order to suitably describe the annual evolution of both gases. Monthly CO₂ and CH₄ percentiles were calculated over a six-year period. Linear trends for most of the percentiles were around 2.24 and 0.0097 ppm year⁻¹, and the interquartile ranges of residuals calculated from detrended concentrations were 6 and 0.02 ppm for CO₂ and CH₄, respectively. Five concentration groups were proposed for CO₂ and six were proposed for CH₄ from the lag-1 autocorrelation applied to detrended observations. Monthly medians were calculated in each group, and combinations of harmonics were applied in an effort to fit the annual cycle. Finally, adding annual and semi-annual harmonics successfully described the cycle where one step was observed in the concentration decrease in spring, not only for high CO₂ percentiles but also for low CH₄ percentiles.

中文翻译：

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伊比利亚半岛北部高原地区CO2和CH4年循环的统计分析

在农村地区，CO ₂和CH ₄观测值中存在异常值。本文的目的是建立基于lag-1自相关的过程以形成测量组，其中一些包括离群值，其余包括常规测量。对观测值进行分类后，第二个目标是确定谐波数，以恰当地描述两种气体的年度逸出量。计算了六年中的每月CO ₂和CH ₄百分位数。对于大多数百分线性趋势是围绕2.24和0.0097 ppm的年^-1，和从除趋势浓度计算残差的四分位数间距分别为6和0.02ppm的对CO ₂和CH₄。从滞后1自相关应用于趋势观察中，提出了五个浓度组用于CO ₂，六个浓度用于CH ₄。计算每组的每月中位数，并应用谐波组合以适应年度周期。最后，添加一年一次和半年一次谐波成功地描述了这样一个周期：不仅对于高CO ₂百分位数，而且对于低CH ₄百分位数，春天的浓度下降都呈阶梯状。