Study of atmospheric CO 2 and CH 4 at Longfengshan WMO/GAW regional station: The variations, trends, influence of local sources/sinks, and transport

Atmospheric CO2 and CH4 have been continuously measured since 2009 at Longfengshan WMO/GAW station (LFS) in China. Variations of the mole fractions, influence of long-distance transport, effects of local sources/sinks and the characteristics of synoptic scale variations have been studied based on the records from 2009 to 2013. Both the CO2 and CH4 mole fractions display increasing trends in the last five years, with growth rates of 3.1±0.02 ppm yr‒1 for CO2 and 8±0.04 ppb yr‒1 (standard error, 1-σ) for CH4. In summer, the regional CO2 mole fractions are apparently lower than the Marine Boundary Layer reference, with the lowest value of‒13.6±0.7 ppm in July, while the CH4 values are higher than the MBL reference, with the maximum of 139±6 ppb. From 9 to 17 (Local time, LT) in summer, the atmospheric CO2 mole fractions at 10 m a.g.l. are always lower than at 80 m, with a mean difference of‒1.1±0.2 ppm, indicating that the flask sampling approach deployed may underestimate the background mole fractions in summer. In winter, anthropogenic emissions dominate the regional CO2 and CH4 mole fractions. Cluster analysis of backward trajectories shows that atmospheric CO2 and CH4 at LFS are influenced by anthropogenic emissions from the southwest (Changchun and Jilin city) all year. The synoptic scale variations indicate that the northeastern China plain acts as an important source of atmospheric CO2 and CH4 in winter.