Improvement of Soil Carbon Determination using laser-induced breakdown spectroscopy

Abstract:

The increase of atmospheric greenhouse gases such as CO₂ has caused noticeable climate change. Since increased CO₂ may contribute to carbon storage in terrestrial ecosystems through the CO₂ cycle between the atmosphere and vegetation, it is necessary to improve methods for measuring C in soil. In this study, we determined the total carbon concentrations of soils using a laser-induced breakdown spectroscopy (LIBS). The LIBS is a minimally destructive measurement technique that uses an ultra-short laser pulse to create plasma on the sample surface via the process of laser ablation. Compared with the traditional C measurements methods techniques such as wet oxidation and dry combustion, LIBS is known as a potentially elegant and promising solution for measuring C in soils. Although previous studies suggested the advantages of LIBS for measuring the C in soils, there are still challenging obstacles to be solved in measuring C. Previous studies have shown that the C in soil can be detected at wavelengths of 193.03 and 247.86 nm. The C line at 247.86 nm shows strong interference with Fe lines at 247.86 nm and 247.95 nm due to overlapping or self-absorption. To dismiss the problem of measuring the C line at 247.86 nm, the C line at 193.03 nm has been used to observe C emission. The C line at 193.03 nm can be quantified without interference from other elements, however, the ratio of Al line (198.90 nm) and Si line (212.40 nm) were used as standardizing factors to develop a significant calibration curve for soils. Although the wavelengths of both 193.03 and 247.86 nm presented the potential to measure C in soils, there has still been a lack of studies comparing the accuracy and effectiveness between the 193.03- and 247.8-nm C lines to analyze soil samples with different chemical and textural characteristics. In this study, we conducted extensive measurements of the C lines at 193.03 and 247.86 nm using LIBS to evaluate the C concentrations of Korean soils with different chemical and physical properties (i.e., wetland, forest, and sediment). The main objectives in this study are (1) to evaluate C concentrations using the C line at 247.86 nm, (2) to evaluate C concentrations using the C line at 193.03 nm and (3) to investigate the advantages and disadvantages of using the two C lines at 193.03 and 247.86 nm.