Comparison of the regional CO2 mole fraction filtering approaches at a WMO/GAW regional station in China

[摘要] The identification of atmospheric CO₂ observation data which areminimally influenced by very local emissions/removals is essential fortrend analysis, for the estimation of regional sources and sinks, and forthe modeling of long-range transport of CO₂. In this study, four approachesare used to filter the atmospheric CO₂ observation records from 2009 to2011 at one World Meteorological Organization/Global Atmosphere Watch(WMO/GAW) regional station (Lin'an, LAN) in China. The methods are based onthe concentration of atmospheric black carbon (BC), on a statistical approach (robustextraction of baseline signal, REBS), on CH₄ as an auxiliary tracer (AUX), and on meteorologicalparameters (MET). All approaches do suitably well to capture the seasonalCO₂ cycle at LAN. Differences are observed in the average regional molefractions with annual values in the REBS method at least 1.7 ± 0.2 ppmhigher than the other methods. The BC method may underestimate the regionalCO₂ mole fractions during the winter–spring period and should betreated with caution. The REBS method is a purely statistical method and itmay also introduce errors on the regional CO₂ mole fractionevaluations, as the filtered trend may be influenced by the "noisy" rawdata series. Although there are correlations between CH₄ and CO₂mole fractions at LAN, the different source/sink regimes may introduce biason the regional CO₂ estimation in the AUX method, typically in summer.Overall, the MET method seems to be the most favorable because it mainlyfocuses on the influence of potential local sources and sinks, and considersdiurnal variations and meteorological conditions. Using the MET method, theannual growth rate of regional CO₂ at LAN is determined to be 3.1 ± 0.01 ppm yr⁻¹(standard error) from 2009 to 2011.

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