The determination of regional CO2 mole fractions at the Longfengshan WMO/GAW station: A comparison of four data filtering approaches

Abstract Using an appropriate method to filter the atmospheric CO 2 mole fractions is not only essential to understand the long-term trend in regional areas but also to study the sources/sinks in the vicinity of the observatory, especially for regional stations where the observed records are frequently influenced by local sources/sinks. In this study, four data selection approaches are used to filter the observed atmospheric CO 2 records from 2009 to 2013 at the Longfengshan (LFS) World Meteorological Organization/Global Atmosphere Watch (WMO/GAW) regional station located in northeastern China. The methods include the methane tracer method (CT), black carbon tracer method (BC), robust extraction of the baseline signal (REBS), and meteorological method (MET). All four methods can accurately capture CO 2 seasonal cycles. However, the CT and REBS induce errors on seasonal value estimations, typically in summer. The BC and MET are better to separate the CO 2 mole fractions into regional or local events, but the BC slightly underestimates the regional CO 2 values during the winter–spring period. In general, the MET is the most reasonable to identify the influence of local sources/sinks and is suitable to be applied at other regional stations. By using the MET, the annual growth rate of regional CO 2 at LFS is calculated to be 3.0 ± 0.8 ppm yr −1 (1−σ) from 2009 to 2013.