| In order to reduce greenhouse gases emission, the key method is obtaining high-precision greenhouse gas flux data and comparing greenhouse gas emissions of different regions. Compared with traditional technology applied in greenhouse gases analyzer, the development of spectrum technology provides high precision technology means for flux observation, and it is more suitable for measurement in the region where signal-to-noise ratio is low, such as small water body. For actual field measurement, we need to verify the applicability and stability of the spectrum analyzer, and clarify the characteristics of different spectrum analyzers. These works can provide reference for the selection and application of analyzer in field observation, but also is an important base for evaluating the quality of flux data. At the same time, these works can promote the application of spectrum technology in atmospheric greenhouse gas monitor.In this study, we set up flux-gradient (FG) and eddy covariance (EC) flux observation systems based on Off-Axis Integrated Output Cavity Spectroscopy(OA-ICOS), Wavelength Modulation Spectroscopy (WMS), and Non-dispersive Infrared (NDIR) Spectroscopy analyzers. Applied the two systems, the greenhouse gas concentration and fluxes were observed high frequently in situ small water body. The experiments verified the applicability and stability of the spectrum analyzer in field observation. At the same time,the differences of these flux observation methods theories were described. The effects of WPL and spectral correction on the raw flux data were found. And,the properties of flux-gradient observation system based on high precision spectrum analyzer for small water body were expounded, the results were as follows:(1) Based on the principles of different spectrum analyzer and measurement results, we found that, the valid data percentage of NDIR and OA-ICOS analyzer were 59% and 89%, respectively for CO2 concentration measurement. And, the measured CO2 concentration by NDIR analyzer was lower than that by OA-ICOS analyzer with 18.10 ?mol mol-1. For H2O concentration measurement, the valid data percentage of NDIR and OA-ICOS analyzer were 63% and 89%, respectively; and the measured H2O concentration by NDIR analyzer was lower than that by the OA-ICOS analyzer with 3.8 mmol mol-1. The deviation caused by system error, the error of atmospheric temperature and pressure fluctuation when density is transformed to concentration, and the drift of the open-path instrument. For the CH4 concentration, the valid data percentage of WMS analyzer and OA-ICOS analyzer were 71% and 91%, respectively. The measured CH4 concentration by WMS analyzer was lower than that by OA-ICOS analyzer with approximately 0.01 ?mol mol-1. Compared high humidity conditions, the deviations among NDIR analyzer, WMS analyzer, and OA-ICOS analyzer were smaller under low humidity condition (Relative Humidity: 30%-40%).The results showed that the influences of atmospheric environmental factors fluctuation on OA-ICOS analyzer was less, compared with other two analyzers.Therefore, the valid data percentage and accuracy of concentration of OA-ICOS analyzer were higher. The analyzer can be selected to measure greenhouse gas concentration in field.(2) The EC and FG flux observation systems set up by different spectrum analyzer can obtain the low signal and capture the temporal variation characteristics of greenhouse gases flux in small water body. Flux-gradient system based on OA-ICOS analyzer can obtain the atmospheric gradient signal. And, zero-gradient test indicated that the flux measurement precision for water vapor, CO2, and CH4 was 0.30 W·m-2, 0.006 mg-(m2 s)-1, and 0.03?g·(m2·s)-1, respectively. Compared with zero-gradient results reported by other literatures, flux-gradient system in this study has high precision and small measurement deviation. The result indicated that OA-ICOS analyzer was suitable for FG flux observation system and can perform high accuracy and stability in filed observation. |
PDF Full Text Request