石油的勘探开发遍布我国各地区, 其产品的应用与工农业生产和人民日常生活密不可分。 石油及石油制品在使用过程中泄漏到土壤中不断累积, 会破坏生态环境。 激光诱导荧光(LIF)是检测土壤中石油烃类有机污染物的重要方法。 激光脉冲能量是LIF的重要实验参数, 对检测灵敏度, 稳定性有显著影响。 为探究土壤中石油烃的激光诱导荧光信号随激发光脉冲能量变化的特性, 以机油为例, 在实验室制备了机油浓度为0.5%~6%的土壤样品, 使用Nd∶YAG激光器作为激发光源, 通过改变266 nm激光的脉冲能量, 获取不同能量密度下油污土壤的荧光光谱。 实验结果表明, 土壤和土壤中机油的荧光光谱强度随激光脉冲能量的增加而增加, 但增加到一定程度后增幅明显减小。 原因是虽然激光能量密度逐渐增强荧光强度也在增强, 土壤中单位面积的有机物含量有限, 部分有机质已经被光解, 有机物被激发的荧光趋于饱和。 在适当的能量密度下, 土壤中机油的荧光强度与其浓度有良好线性关系。 实验发现, 随着激光能量密度的减小, LIF系统测量机油的平均相对误差先减小后增大, 其原因是, 当激光能量密度小于一定范围时, 信号的信噪比随之减小, 因此测量的平均相对误差逐渐增大; 当激光能量密度大于一定范围时, 虽然信号的信噪比随之增大, 但已经逐渐超出系统最佳的测量范围, 所以测量的平均相对误差逐渐增大。 当激光能量密度在2.4~4.0 mJ·cm^-2时, 土壤中机油的荧光强度随激光脉冲能量密度线性增强, 且对机油浓度的测量误差均小于2.5%, 检测限在200~300 mg·kg^-1之间。 当能量密度大于4.0 mJ·cm^-2时, 机油的荧光强度增幅显著降低, 测量误差也随之增大。 因此, 兼顾LIF测量土壤中机油的平均相对误差和测量检测限, 激光脉冲能量选择2.4~4.0 mJ·cm^-2较优。 所述方法也可扩展其他土壤中石油烃荧光信号检测。

The exploration and development of petroleum is spread all over the country, and the application of its products is inseparable from the industrial and agricultural production and the daily life of the people. In the use of petroleum and petroleum products, they leak into the soil and accumulate, which will destroy the ecological environment. Laser-Induced fluorescence (LIF) is an important method to detect petroleum hydrocarbon organic pollutants in soil. Laser pulse energy is an important experimental condition of LIF. It has a significant impact on detection sensitivity and stability. In order to explore the characteristics of LIF signal of petroleum hydrocarbons in soil with the pulse energy of excitation light, taking oil as an example, soil samples with machineoil concentration of 0.5%~6% were prepared in the laboratory. The Nd∶YAG laser was used as an excitation source with a wavelength of 266 nm. The fluorescence spectrum of the oily soil at different energy densities was obtained by changing the pulse energy of the 266 nm laser. The experimental results showed that the fluorescence intensity of the oil in the soil had a good linear relationship with its concentration at different energy densities. The fluorescence intensity of the machineoil in the soil itself and in the soil increased as the laser pulse energy increased. The experiment found that as the laser energy density decreased, the average relative error of the LIF system when measuring the oil first decreased first and then increased. The reason was that when the laser energy density was less than a certain range, the signal-to-noise ratio of the signal decreased. Therefore, the average relative error of the measurement gradually increased; when the laser energy density was larger than a certain range, although the signal-to-noise ratio of the signal increased, it had gradually exceeded the optimal measurement range of the system, so the average relative error of the measurement gradually increased. When the laser energy density wasin 2.4~4.0 mJ·cm^-2, the fluorescence intensity of the oil in the soil increased linearly with the laser pulse energy density, and the measurement error of the machine oil concentration was less than 2.5%. At this time, the system limited the detection of machineoil to between 200~300 mg·kg^-1. When the energy density was greater than 4.0 mJ·cm^-2, the increase of the fluorescence intensity of the machineoil was significantly reduced, and the measurement error also increased. Therefore, taking into account the system to measure the average relative error of the machineoil in the soil and the measurement limit, the laser pulse energy was preferably 2.4~4.0 mJ·cm^-2. In this paper, the characteristics of the fluorescence signal of the machine oil in the soil as a function of the excitation light energy were studied. The method could be extended to study the fluorescence signals of other petroleum hydrocarbons in soil. This paper provided a reference for the formation of LIF system to measure petroleum hydrocarbons in the site and select better laser energy conditions.