Study on the in-situ measurement of atmospheric CH₄ and CO by GC-FID method at the Shangdianzi GAW regional station

In-situ GC-FID system for atmospheric CH₄ and CO mixing ratio measurements at the Shangdianzi (SDZ) GAW regional station in Beijing was designed and optimized in 2009 based on a comparable system at the Waliguan GAW global station in Qinhai. Results from this study indicate that the system's precisions for CH₄ and CO are higher than 0.03% and 0.45% respectively, which can meet the quality target on background greenhouse gas observations by the World Meteorology Organization's Global Atmosphere Watch (WMO/GAW) program. The selection method of working standards for this system was established: two working standards(WH for the high concentration and WL for the low concentration) were selected, the concentrations of CH₄ and CO in these two standards can cover the ambient mixing ratios of CH₄ (2007.1×10^-9 and 1809.5×10^-9) and CO (405.6×10^-9 and 123.8×10^-9), an injection sequence was programmed so that the two standards were analyzed alternatively for every three runs. The measurement accuracies are high, as shown by the standard deviations less than 1.7×10^-9 and 1×10^-9, for CH₄ and CO, respectively. This method has been applied to in-situ measurement of atmospheric CH₄ and CO in North China.