Authors

Abstract

In the context of agricultural emissions in China, it is common for fields to be bordered by row windbreaks, which - when located downwind of emission sources - can complicate gas flux measurements. To address this challenge, the environmental adaptability of a laser-based detection system for quantifying gas emissions from agricultural sources was evaluated through a controlled gas emission field simulation experiment. Using methane as a representative gas, a flux measurement system based on open-path laser absorption spectroscopy was developed. The study employed an artificially simulated methane volatilization source and two measurement devices to conduct experiments under three conditions: an ideal environment, a laser path positioned downwind of the source, and a laser path set directly above the source. Results show that the standard deviations of the ratio QbLS/Q were 0.0277, 0.0283, and 0.0256, respectively. The corresponding maximum fluctuation amplitudes were 7.3%, 7.4%, and 5.9%. These findings suggest that for a row windbreak located downwind of an emission source, selecting an optimal measurement strategy - such as positioning the optical path above, across, or near the vertical downwind axis of the source - can minimize environmental interference and enhance the reliability of methane flux measurements in agricultural settings.

Abstract in Chinese

针对我国农业排放问题，田间地头常常会设置一排防风林。假设防风林位于被测源的下风向，这可能会使测量变得复杂。鉴于这种情况，在气体排放田间模拟实验中，以甲烷为例，对基于激光探测确定农业源气体排放的环境适应性进行了评估。建立了基于开放光路激光吸收光谱技术的甲烷通量测量系统。通过使用人工模拟的甲烷挥发源和两套测量装置，分别开展了理想环境下、源下风向以及源上方环境下的实验。结果表明，理想环境下 QbLS/Q 的标准偏差为 0.0277。源下风向得到的 QbLS/Q 标准偏差为 0.0283。源上方设置得到的 QbLS/Q 标准偏差为 0.0256。QbLS/Q 的最大波动幅度分别为 7.3%、7.4% 和 5.9%。由此可见，对于一排防风林，假设其位于被测源的下风向，通过优化测量方法可降低气体通量的估算误差。在测量实际大面积面源时，从源的下风向进行测量，并且可以将光路设置在源垂直下风向的上方，穿过源或靠近源。这种测量方法减少了上风向防风林造成的局部环境干扰，从而实现测量。