## 1 Introduction  
The environmental impact of coal-fired power generation is growing. Korea is still considerably dependent on coal as an energy source due to price competition. The contribution ratio of coal-fired power plants to total emission by air pollutants is 2.7% for total suspended particles, 3.7% for particle matter 10 (PM10), 4.7% for particle matter 2.5 (PM2.5), 16.2% for nitrogen oxides (NOx), and 24.1% for sulfur oxides (Sox) in Korea, according to the Korea national institute of environmental research data [1]. According to this report, the summation of SOx and NOx has the largest proportion, at over 40%. In the case of NOx emitted from coal-fired power plants, most of the combined nitrogen comes from the combustion air and should be controlled through a denitrification facility. On the other hand, in the case of Sox, the use of fuel containing a small amount of sulfur is recommended, because the sulfur comes from the fuel itself [2]. By using in situ measurement techniques for determining the calorific value of the coal and sulfur concentration within the coal, it can be possible to control of the excessive amounts of combustion air and warnings can be given about excessive sulfur concentrations in the non-uniformly mixed coal. Conventional techniques for quantitatively analyzing element concentrations usually need complicated sample pretreatment such as fusion dissolution and microwave digestion data processingand require standard reference materials. Due to these problems, analyzing many samples can be expensive and quite time-consuming [3]. Thus, a fast and reliable analysis method is required. To overcome these limitations of conventional analysis methods, many studies have been conducted measuring the element concentration of coal using spectroscopy methods. [PERSON] et al. [4] conducted a study to measure the values of coal using mid-infrared spectroscopy. In this study, the results of three modes of the multiplicative scatter correction (MSC) data preprocessing method were detailed. The minimum value of the average root mean square error (RMSE) of sulfur was 37.36%, which was somewhat high. [PERSON] et al. [5] conducted a near-infrared (NIR) spectroscopy study on the measurement of various properties from four types of coal by applying multivariate statistical techniques. The minimum value of the percentage error of the mean RMSE of sulfur was 8.98% for full sample sets, and the averaged mean RMSE of all kinds of the coal samples was 13.53%. These values were considerably lower than those of the mid-infrared spectroscopy study. In recent times, research on a technology called laser-induced breakdown spectroscopy (LIBS) have been actively conducted. LIBS is a spectroscopic method using lasers. Qualitative and quantitative analysis of elements is possible, including lighter elements in the periodic table, regardless of their states of gas, liquid or solid. A small quantity of mass on the sample surface is ablated by a focused high energy laser beam. The plasma is then generated and expanded above the sample surface. Discrete atomic lines are emitted after a cooling process [6]. This emitted light can be collected by a spectrometer and used for qualitative and quantitative elemental analysis. LIBS has been successfully applied in various fields, especially for element analysis. [PERSON] et al. [7] quantitatively identified the elemental composition of preservative-treated wood using principal component analysis (PCA). In another study, [PERSON] et al. [8] studied a set of fertilizer samples to reveal the correlation of phosphorus and potassium using the partial least square (PLS) regression analysis method. These studies suggest that elemental analysis with LIBS is feasible and can be applied to sulfur concentration analysis. In fact, some studies have attempted to measure the sulfur concentration using LIBS. [PERSON] et al. [9] tried to use single-pulse and double-pulse laser irradiation approaches to apply LIBS to on-line sulfur analysis of minerals under ambient conditions.