At present, China is actively implementing dual control of total energy consumption and intensity. The "14th Five Year Plan for Ecological Environment Monitoring" issued by the Ministry of Ecology and Environment specifically points out the promotion of the development of carbon emission measurement technology and the organization of multiple key industry enterprises to carry out pilot work on monitoring greenhouse gas emissions such as carbon dioxide and methane; Establish a greenhouse gas monitoring network for key cities and upgrade the greenhouse gas monitoring function of the national atmospheric background station. Therefore, conducting greenhouse gas monitoring within the environmental protection systems of each province (municipality) and prefecture (state) has become an important task. Methane, carbon dioxide, nitrous oxide, and sulfur hexafluoride are the main analytical targets of China's greenhouse gas monitoring network. Their emission sources are different, and the concentration difference between different types can reach up to 6 orders of magnitude (for example, the CH4 content in ambient air is about 1-2 ppm, and the SF6 content is between 9-15 ppt). Accurate monitoring of these four types of gases requires high-sensitivity detection methods. In terms of monitoring accuracy, GB/T 31705-2015 [1] requires monitoring techniques to obtain quantitative accuracies of CO2 and CH4 that are better than 0.05% and 0.1%, respectively, after 10 repeated analyses of standard samples with concentrations close to actual greenhouse gases. For the other two gases N2O and SF6 not covered by the GB/T 31705-2015 method, the National Environmental Protection Agency requires monitoring reproducibility to be better than 0.1% (for N2O) and 0.5% (for SF6), respectively.

The high-precision environmental greenhouse gas monitoring scheme mainly adopts online equipment based on cavity ring down spectroscopy (CRDS) technology. The measurement accuracy of such devices varies slightly for different greenhouse gases, but is generally better than 0.05%. However, CRDS technology is not suitable for measuring SF6 and needs to be combined with other technologies used for measuring SF6 in practical applications to achieve monitoring of target compounds. The use of different analytical techniques requires higher experience and skills from operators, and the combination of different analytical platforms increases the cost of greenhouse gas monitoring. Developing a technology platform/solution based on laboratory wide applications, providing reliable/high-precision monitoring results, is particularly important for establishing a greenhouse gas monitoring network. Gas chromatography technology is one of the important candidate platforms in the development process of this scheme.

The practice of using gas chromatography to detect greenhouse gases has a long history. The traditional method uses gas valve injection, and a thermal conductivity detector (TCD) and a hydrogen flame ionization detector (FID) are connected in series to detect CO2 and CH4 respectively, or a methane converter and FID are used in the same channel to detect CO2 and CH4 [2], and an electron capture detector (ECD) is used to detect N2O. The analysis accuracy of CO2, CH4, and N2O obtained using this configuration can reach 0.2% -0.5%, but it is difficult to break through to<0.1%, which cannot meet the current requirements for accuracy and precision in greenhouse gas monitoring; And there are few reports on the accuracy of SF6 analysis at the concentration level of PPT in traditional methods. In order to monitor trace amounts of CO2, CH4, N2O, and ultra trace SF6 on the same gas chromatography system and meet strict analytical accuracy and precision requirements, it is necessary to optimize the scheme from multiple factors such as injection, separation, and detection, and achieve flexible configuration expansion to meet future analytical expansion needs (such as adding trace CO analysis to air).

This article demonstrates that the Agilent 8890 gas chromatograph achieves high-precision monitoring of four key greenhouse gases by optimizing the injection volume/controlling injection reproducibility, using multi-channel analysis and high-sensitivity detectors, optimizing the analysis flow path to ensure long-term stable operation of the system.