Study Of Techniques And Methods For Measuring Emissions Of Greenhouse Gases And Stable Isotopes

Global warming due to the increase in the atmospheric greenhouse gases has become a serious environmental problem facing the world.In order to control the emissions of the greenhouse gases, we need to better understand the distributions of natural carbon sources and sinks, as well as the basic processes and variation of the emissions of the greenhouse gases in the ecosystem, so the active techniques for measuring the emissions of greenhouse gases from ecosystem sources are required. Such environmental stable isotopes as carbon thirteen and deuterium are widespread in the atmosphere, hydrosphere, and biosphere,and can be used to research the dynamic processes of the formation, transfer, and consumption of greenhouse gases. Therefore, in addition to multiple greenhouse gases, the stable isotopes should be considered for monitoring ecological emission.The focus of the paper is development of key methods and techniques for monitoring emissions of greenhouse gases from ecosystem sources,based on new methods of Fourier transform infrared spectrometry(FTIR) for measurement of multi-component greenhouse gases.In our work,the real time methods of concentration retrieval for multiple greenhouse gases(carbon dioxide,water vapor, methane,nitrous oxide) and the stable isotopes of carbon dioxide and water vapor have been studied using an open-path FTIR system. Also,a model for retrieval of emissions of greenhouse gases are developed,and the methods for measurement of emissions of greenhouse gases and the isotopic flux are examined.Furthermore, experimental verification has been conducted for our measurement system and methods.Firstly, the methods for detecting greenhouse gases and their stable isotopes have been deliberated, based on the unique absorption features of gas species in infrared spectral region. The criteria in selection of wavelength region for retrieval of greenhouse gases and stable isotopes are discussed, and the spectral windows for analysis of each gas component of interest are determined.As well, the measurement parameters of the open-path FTIR system are studied,including experiments and tests carried out in a laboratory environment and field environment.The measurement accuracy and precision of the whole system for detecting the ambient air are given.On this basis, a model for retrieval of emissions of greenhouse gases are constructed, which combines an inverse dispersion technique based on a backward Lagrangian stochastic (bLS)model with an open-path FTIR system. Then, numerical simulations and a field experiment of release of high purity sample gas are conducted, in which emission-calculation errors caused by the assumption in application of the bLS model are discussed, and a reasonable sensor configuration for complex sources is identified. The experimental results show the feasibility and accuracy of the measurement system in conjunction with the model for measuring emissions of greenhouse gases.Finally, greenhouse gases and stable isotopes of CO2and H2O in ambient air are continuously measured in a half-month field experiment, and the variation of stable isotopes of CO2and water vapor as well as the isotopic ratios δ13C and δD are investigated. The time series of stable isotopes of CO2and water vapor are analyzed on different time scales by Keeling plot methods, and the deuterium isotopic characteristics of evapotranspiration are determined. Moreover, the surface flux of12CO2and13CO2are calculated preliminarily, and this is a new attempt to measure isotopic flux in ecosystem. The results of the field experiment indicate the feasibility of our measurement techniques and methods for detecting greenhouse gases and stable isotopes.Also,the outcomes demonstrate the potential of our measuring system for long term, continuous, unattended measurement of ambient air and source emissions.