In situ measurement of atmospheric CO₂ at the four WMO/GAW stations in China

Abstract. Atmospheric carbon dioxide (CO₂) mole fractions were continuously measured from January 2009 to December 2011 at four atmospheric observatories in China using cavity ring-down spectroscopy instruments. The stations are Lin'an (LAN), Longfengshan (LFS), Shangdianzi (SDZ), and Waliguan (WLG), which are regional (LAN, LFS, SDZ) or global (WLG) measurement stations of the World Meteorological Organization's Global Atmosphere Watch program (WMO/GAW). LAN is located near the megacity of Shanghai, in China's economically most developed region. LFS is in a forest and rice production area, close to the city of Harbin in northeastern China. SDZ is located 150 km northeast of Beijing. WLG, hosting the longest record of measured CO₂ mole fractions in China, is a high-altitude site in northwestern China recording background CO₂ concentration. The CO₂ growth rates are 3.7 ± 1.2 ppm yr⁻¹ for LAN, 2.7 ± 0.8 ppm yr⁻¹ for LFS, 3.5 ± 1.6 ppm yr⁻¹ for SDZ, and 2.2 ± 0.8 ppm yr⁻¹ (1σ) for WLG during the period of 2009 to 2011. The highest annual mean CO₂ mole fraction of 404.2 ± 3.9 ppm was observed at LAN in 2011. A comprehensive analysis of CO₂ variations, their diurnal and seasonal cycles as well as the analysis of the influence of local sources on the CO₂ mole fractions allows a characterization of the sampling sites and of the key processes driving the CO₂ mole fractions. These data form a basis to improve our understanding of atmospheric CO₂ variations in China and the underlying fluxes using atmospheric inversion models.